Progress in the construction strategy of noble metal active sites for zeolite-based PNA and VOCs catalysts

Abstract

Zeolite-loaded noble metal catalysts have demonstrated excellent performance in addressing cold-start automotive exhaust NOx emissions and catalytic oxidation of VOCs applications. Pd and Pt are the most commonly used active metals in PNA and VOC catalysts, respectively. However, despite the same metal/zeolite composition, the efficient active sites for PNA and VOC catalysts have been viewed as mainly Pd2+ and Pt0, respectively, both of which are different from each other. As a result, various methods need to be applied to dope Pd and Pt in zeolitic support respectively for different usages. No matter which type of metal species is needed, the common requirement for both PNA and VOC catalysts is that the metal species should be highly dispersed in zeolite support and stay stable. The purpose of this paper is to review the progress of synthetic means of zeolite-coated noble metals (Pd, Pt, etc.) as effective PNA or VOC catalysts. To give a better understanding of the relationship between efficient metal species and the introduced methods, the species that contributed to the NOx adsorption (PNA) and VOCs deep catalytic oxidation were first summarized and compared. Then, based on the above discussion, the detailed construction strategies for different active sites in PNA and VOC catalysts, respectively, were elaborated in terms of synthetic routes, precursor selection, and zeolite carrier requirements. It is hoped that this will contribute to a better understanding of noble metal adsorption/catalysis in zeolites and provide promising strategies for the design of adsorption/catalysts with high activity, selectivity and stability.

Headnote

Received 16 January 2024; revised 26 April 2024; accepted 4 June 2024 Available online 8 June 2024

Abstract

Zeolite-loaded noble metal catalysts have demonstrated excellent performance in addressing cold-start automotive exhaust NOx emissions and catalytic oxidation of VOCs applications. Pd and Pt are the most commonly used active metals in PNA and VOC catalysts, respectively. However, despite the same metal/zeolite composition, the efficient active sites for PNA and VOC catalysts have been viewed as mainly Pd2+ and Pt0, respectively, both of which are different from each other. As a result, various methods need to be applied to dope Pd and Pt in zeolitic support respectively for different usages. No matter which type of metal species is needed, the common requirement for both PNA and VOC catalysts is that the metal species should be highly dispersed in zeolite support and stay stable. The purpose of this paper is to review the progress of synthetic means of zeolite-coated noble metals (Pd, Pt, etc.) as effective PNA or VOC catalysts. To give a better understanding of the relationship between efficient metal species and the introduced methods, the species that contributed to the NOx adsorption (PNA) and VOCs deep catalytic oxidation were first summarized and compared. Then, based on the above discussion, the detailed construction strategies for different active sites in PNA and VOC catalysts, respectively, were elaborated in terms of synthetic routes, precursor selection, and zeolite carrier requirements. It is hoped that this will contribute to a better understanding of noble metal adsorption/catalysis in zeolites and provide promising strategies for the design of adsorption/catalysts with high activity, selectivity and stability.

© 2024 Institute of Process Engineering, Chinese Academy of Sciences. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Keywords: Noble metal; Zeolites; Constructing strategy; PNA; VOCs

1. Introduction

Volatile organic compounds (VOCs) and nitrogen oxides (NOy) are crucial precursors to the formation of near-surface O3 and PM, s, contributing significantly to global environmental issues like ozone and photochemical smog. These are the primary pollutants found in exhaust emissions from both stationary and mobile sources [1]. In order to address the sever impacts of NO, and VOCs on the environment and human health, the government has placed increasing emphasis on controlling emissions of these pollutants by enacting a series of emission regulations and related requirements. In November 2021, China released "Opinions on Deepening the Fight Against Pollution", proposing to vigorously promote the nitrogen oxides (NOx) and volatile organic compounds (VOCs) emission abatement, making it clear that by 2025, the total emissions of VOCs and NO, would have decreased by more than 10% compared to 2020, respectively [2].

According to the statistics from Ministry of Ecology and Environment [3], NO, emissions in China's exhaust gas in 2020 were 1019.7 million tons, mobile sources NO, emissions accounted for 55.6%, diesel vehicles, in particular, are a major contributor to the problem of high NO, emissions. This is mainly because of their oxygen-rich lean combustion and high combustion temperature. To address this issue, various NO, purification technologies have been reported in scientific literature, including selective catalytic reduction (SCR), selective non-catalytic reduction (SNCR), absorption, adsorption, and non-thermal plasma (NTP) [4]. Among these technologies, ammonia selective catalytic reduction (NH3-SCR) stands out as the most efficient method to reduce NO, in diesel vehicles. It has been proven to successfully remove nitrogen oxides at temperatures above 200 °C. Metal-modified zeolites have also shown great potential as highly efficient SCR catalysts. However, the current state-of-the-art Cu/SSZ-13 catalyst faces a significant challenge when it comes to low-temperature activity (< 150 °C) during the cold-start period of vehicles [5]. To tackle this issue, Johnson-Matthey has formed a very efficient cold start catalyst: Passive МО, Adsorber (PNA). This catalyst can effectively absorb NO at low temperatures, and then desorbs the NO, after the temperature reaches the NH;-SCR catalyst starting temperature. For the elimination of VOCs, the commonly used techniques include recovery and destruction [6]. Recovery mainly separates the VOC from the gas by physical action, including adsorption, solution absorption, condensation, and membrane separation. Absorption can effectively remove high concentration of VOCs, but usually bring the problem of subsequent spent solvent treatment [7]; Valuable concentration VOCs can be recovered by condensation, but the removal process is costly and spent coolant disposal is difficult [8,9]; Adsorption have many advantages include minimal energy consumption, facile operation and absence of secondary pollution, but is only applicable to the removal of lower concentrations of VOCs, necessitating frequent regeneration of the adsorbent [10,11]. Unlike recovery, destruction methods can eradicate VOCs and transform them into harmless CO, and water, including direct combustion, catalytic oxidation, biodegradation, plasma oxidation, and photocatalytic oxidation techniques. Among them, catalytic oxidation is considered to be an effective technique due to its economic feasibility, high efficiency, low formation of secondary pollutants, and the ability to operate at lower temperatures with controlled selectivity for specific by-products [12].

Noting that no matter for adsorption or catalytic oxidation methods to purify МО, or VOCs, the removal efficiency is highly dependent on the performance of adsorbents or catalysts. Among the two types of materials (transition metal oxide and zeolite supported with the noble metals of Pt, Pd, and Ag) currently applied as PNA [13], the latter although proposed later than the former, has garnered more attention due to its capacity for МО, storage, anti-poisoning properties, and resistance to hydrothermal aging [5,14]. Particularly, Pd loaded at zeolites like SSZ-13, SSZ-39, Beta, and ZSM-5, etc. has become one of the most promising commercialization potentials among the mainstream PNA catalytic materials due to their exceptional ability to store МО, at low temperatures and the appropriate temperature required for NO, desorption [15]. The catalytic oxidation of VOCs is commonly accomplished using two types of catalysts similar to PNA: catalysts supported by noble metals and transition metal oxides [16]. Although expensive, noble metal-based catalysts are preferred due to their high specific activity, resistance to deactivation, and ability to be regenerated [16-18]. Pt, Pd, Au, Ag, Rh, etc. are often used as active components, among which Pt and Pd have become the hot topic due to their better low-temperature activity, high stability, and a wider range of applications for different types of VOCs [19,20]. Materials commonly used as supports to load noble metal include metal oxides (CeO,, СозО4, Al,O3, etc.), activated carbon, and zeolites. Among these support materials, zeolite shows outstanding properties for highly dispersing and anchoring the metal species to generate active sites due to its effective large specific surface, regular pore structure, and adjustable acidity [21-25].

The form and distribution of noble metals introduced into zeolites, which directly determine the performance of noble metal zeolites as adsorption/catalytic materials, typically depends on several factors, including preparation methods, types of precursors, metal loading & particle size, as well as the structural properties of support materials et al. [26-29]. Therefore, the significance of this review is to summarize and analyze the active site fabrication methods of PNA and VOC catalytic oxidation catalysts to find the most suitable strategy for constructing highly efficient PNA and VOC catalysts. In detail, the application of noble metals/zeolites as PNA and VOC catalytic combustion catalysts was first reviewed to elucidate the differences and commonalities in both types of active species and the corresponding mechanisms in different application scenarios. Subsequently, progress in fabrication methods for different active sites on adsorbents and catalysts is reviewed with emphasis on differences in synthesis strategies, precursor selection, and requirements for zeolite carriers. This review aims to enhance our understanding of the adsorption/ catalytic mechanisms of noble metals zeolites and propose promising strategies for the design of adsorption/catalysts with high activity, selectivity and stability.

2. Recognition of active sites on noble metal/zeolite-based PNA and VOC catalysts

Different pollutants require different requirements for noble metal zeolite materials used as passive МО, adsorbers or VOCs catalysts, with varying active components and species. This section discusses the applications of these materials separately in PNA and VOCs catalysis, highlighting the specific precious metals and active species used in different scenarios.

2.1. NO, passive adsorption

Noble metals (Pd, Pt, Ag, Ru) have a unique electronic structure with many empty d orbitals, small energy level spacing, easy coordination, and strong adsorption capacity. Due to the expensive price and excellent atomic activity of noble metals, they are often dispersed and loaded on supports for application to improve the utilization of noble metals. It was found that the noble metal-based materials have excellent low-temperature activity, moderate adsorption and desorption strengths, and good stability, they have been widely developed as PNA for МО, capture during vehicle cold-start period. However, different noble metals exhibit different performances as PNA because of their different properties. Table 1 briefly summarizes some of the current noble metal-based PNA material's compositions and properties.

Pt-based materials were first found to be used as NO, adsorbents in the last century [41]. Compared with other noble metals, Pt has excellent sulfur resistance [42,43], and the interaction of SO, with Pt-based materials only promotes the oxidation of SO, to SO; without further formation of reactive PtSO, leading to Pt poisoning. However, the NO, adsorption capacity of the Pt-based materials was limited in the first 200 s during the actual cold-start exhaust emission process [44], Ji et al.'s experiment showed less than 30% NO, storage efficiency at 80 °C. Moreover, due to the preferential storage of NO, as heat-stabilized nitrate in the Pt/Al,O5 [30], a high desorption temperature is required, which makes the practical application more difficult. Due to the high cost of platinum group metals, other inexpensive noble metals were considered. In 2014, Agbased materials were observed to effectively adsorb МО, at 150-300 °C [45]. However, the temperature window was too high to achieve cold-start adsorption, so Ag-based materials were optimized [31,32,46,47]. For instance, the effective dispersion of Ag particle size using MgO-modified carriers dramatically increased the NO, adsorption capacity [32], and the excellent NO, storage (0.22 g Lh of Ag/Al,O- at 75- 200 °C was achieved using H, assistance [31]. Nevertheless, the desorption temperature of NO, on Ag-based materials was too high (~430 °C), and the results of the sulfur resistance test indicate that Ag-based materials are highly vulnerable to sulfur poisoning [31]. Therefore, despite their extremely significant cost advantages, Ag-based materials are still not suitable as cold-start NO, adsorption materials. Recently, atomically dispersed Ru/CeO, materials have been reported to have excellent PNA performance, with cold-start NO, adsorption of only 0.5 wt% Ru/CeO, reaching 120 pmol g ' [34] (Table 1). However, in the literature, materials containing Ru (typically in the form of Ru/RuO, nanoparticles rather than atomically dispersed Ru) are often regarded as having volatility issues, This is because they can form highly volatile and relatively toxic КиО, oxides [48]. Therefore, the possibility of Ru as the active component of PNA materials still needs a lot of experimental research.

Compared with the above materials, the Pd-based PNA materials exhibited superior МО, adsorption performance and more suitable desorption temperature [44,49-51]. In the experiments of Toops et al. [51] the NO, adsorption of Pd-based PNA (28 ито! g ') was much larger than that of Ag-PNA (2 pmol g ') during the first 3 min, and 90% of the stored NO, was released below 300 °C during subsequent warming desorption. Analogously, according to Jones [49], compared with the desorption temperature of Pt/CeO, material which was greater than 400 °C, the Pd/CeO, exhibited a desorption temperature more in line with the operating temperature window of the PNA (< 350 °C) and excellent cycling performance, and the excellent NO, adsorption capacity was still maintained after 5 cycles at 350 °C. Recent research conducted by Chen et al. [14] has garnered considerable attention towards the utilization of Pd-promoted zeolite materials. As shown in Fig. la, it can be observed that at the conclusion of the 2-min period for NO storage, the Pd/CeO, sample demonstrates a lower trapping efficiency compared to the three Pdzeolite samples, and the total quantity of NO stored on the Pd/ CeO, material is significantly reduced [14]. More importantly, in the sulfur resistance evaluation experiment, the Pd/CeO, sample experiences complete deactivation after sulphation, however, the three Pd-zeolite samples retain a majority of their NO storage capacities [14] (Fig. 1b). In addition, compared with metal oxide-based PNA, zeolite-based PNA also has better water resistance at low temperatures, and can still retain some NO, adsorption capability in the presence of water. Therefore, when considering factors such as trapping efficiency, storage capacity, and resistance to sulfur poisoning and water, Pd-promoted zeolites emerge as the most appealing and potentially valuable PNA material when compared to metal oxide systems [14, 30,52-54].

Identifying effective adsorption sites and clarifying the mechanism of their interaction with NO, is the key to designing and optimizing PNA with high МО, storage performance, high stability, and long lifetime [37]. First of all, for Ag-based PNA, most of the research focuses on Ag-loaded metal oxides as low-temperature NO, adsorbents. Among them, Ag,0 as the adsorption site of NO, at low temperature, can effectively oxidize NO to No to store it on the active Ag site in the form of nitrate. However, the storage efficiency is low, so the researchers have developed the use of H, assisted to promote the oxidation of NO to NO,, nitrate storage increased significantly, and in the subsequent heating process in the form of NO, desorption [31,46,47,55]. However, H, was not detected in the exhaust of lean-burn diesel engines, there by greatly limiting the potential use of Ag/Al,O; in lean-burn conditions. On Pt/oxide catalysts, both PtO and Pt sites can promote the storage of NOx, but the storage mechanism is not consistent. Ji et al. [3] revealed that FTIR spectra obtained from Al,O; during NO storage showed similarities to those observed in Pt/Al,O3, indicating that NO is mainly stored on Al,O5 rather than on Pt sites in Pt/Al,O; catalysts. Further analysis indicated the dominance of PtO in the PALO; catalyst, which is shown to be inert in terms of NO storage. Nevertheless, it is worth noting that the presence of PtO sites enhances the rate of NO oxidation to МО», which enhances the adsorption capacity of Pt/Al,O; for NO by promoting nitrate formation on Al,Os. Similarly, the inclusion of H, can also effectively enhance the NO storage capacity of Pt/Al,O3. H> reduces the oxidized Pt to metallic Pt and adsorbs NO in the form of Pt°-NO complex, thereby improving the low-temperature NO adsorption capacity of Pt/Al,O3 [30]. A similar phenomenon was also observed by Theis et al. [44]. Before the NO adsorption test, they treated Pt/Al,O; with 3% CO and 1% H, at 350 °C, which effectively improved the low-temperature NO, storage capacity of Pt/A1,0;. Unfortunately, the reduction of Pt significantly increases the desorption temperature of NOx. Under 250 °C, less than 10% of the stored NO, is released. This can be attributed to the ability of metallic Pt to oxidize the released NO to NO,, which can then be readsorbed to form a thermally stable nitrate that needs high temperature to release.

In comparison to other materials, Pd/zeolite materials are rich in adsorption sites, exhibit good low-temperature activity, and the adsorbed NO, can be easily separated at suitable temperatures, which have a large desorption amount. Typically, during the adsorption process of NO, common active sites include charge-compensated ionic Ра?! (Z Pd"·Z- and Z [PdOH]·) and Pd· in the zeolite backbone and PdO, sites distributed on the outer surface of the zeolite [37,56]. As shown in Fig. 2, Pd·" ions can directly coordinate with NO to form linear nitrosyl species, or through an OH" group for charge equilibration to form Z [PdOH]·. Z [PdOH]· site can be easily reduced by the adsorbed NO species to the Z Ра" site, which is also capable of adsorbing NO, and the adsorbed NO is more stable [57]. Among them, isolated Ра?" ions serve as the most stable adsorption sites at low temperatures when exposed to NO [35]. For example, according to the computational analysis of Mandal et al. [58], on SSZ-13 zeolite, Pd" and [PdOH]· landing in the 6 MR or the 8 MR are compensated by a T-Al site charge, respectively, while Pd"· landing in the 6 MR is balanced by a pair of T-Al sites, showing excellent stability in NO adsorption experiments. Density functional theory (DFT) and spectroscopic characterization establish that a Pd cation will preferentially exchange at 6 MR Z, sites instead of forming Z Ра" or Z [РАОН]". For PdO, species, it is generally accepted that it is the PdO, species that acts as an effective NO, adsorbent rather than PdO. For instance, in experiments conducted by Lee [59], after removing Ра?" on Pd/SSZ-13 leaving only PdO particles, the material's NO, adsorption capacity was significantly reduced, retaining only about 10% of the original capacity. It has also been suggested that the PdO site can adsorb NO and react with O, to form РаМОз, but the adsorption is too slow to play an effective role during the short period of automobile cold start [60]. The PdO, site can effectively adsorb NO, at low temperatures. In situ XPS showed that during the adsorption process, NO adsorbed on PdO, sites was converted to NO», and the ratio of NO depletion to NO, production was 2:1, indicating that PdO, has the ability to adsorb two NO molecules, with one of them being converted to NO, while the other remains in a molecularly adsorbed state [37]. Additionally, the zeolite support itself provides rich Brgnsted sites, which contribute to the storage capacity by adsorbing NO as NO". However, at temperatures between 100 and 200 °C, the adsorbed NO easily desorbs. It is important to mention that the above-mentioned NO storage processes occur in the absence of H,O. Numerous experiments have demonstrated that the presence of H,O in the feed gas significantly inhibits NO, adsorption at both Pd(IV) and zeolite Brgnsted site [37,56,59,61]. As shown in Fig. 3, in the presence of water, the amount of NO, adsorption of the three samples was significantly reduced, and the PdSSZ-13 adsorbent containing the most ultrafine PdO, clusters was the most inhibited [37]. Thus, Pd"· ions are identified as the most efficient active sites for NO storage due to their high storage efficiency, water resistance, and superior activity at low temperatures [62].

2.2. VOCs catalytic combustion

Among the catalysts used for the oxidation of volatile organic compounds (VOCs), noble metal-based catalysts, including Pt, Pd, Au, and Ag, have been extensively studied. This is because noble metals exhibit high activity in the oxidation or reduction of hydrocarbons. Table 2 presents the different types of noble metals suitable for different VOC molecules are different. For example, are more effective in catalyzing the oxidation of short-chain hydrocarbons compared to Pt-based catalysts. Based on the sequence of reactions, the oxidation mechanisms of VOCs can be classified into three types. Fig. 4 [16,63,64] illustrates these mechanisms: the Eley-Rideal (E-R) mechanism (Fig. 4a), where the catalytic process occurs between adsorbed oxygen species and VOC molecules in the gas phase; the Langmuir-Hinshelwood (L-H) mechanism (Fig. 4b), where the reaction occurs between adsorbed oxygen species and adsorbed VOC molecules; and the Mars-van Krevelen (MVK) mechanism (redox mechanism) (Fig. 4c), where the reaction process take place between adsorbed VOC molecules and surface lattice oxygen on the catalysts. According to literature, the L-H mechanism is favored for Ag, Au, Pt, and Pd catalysts, involving a reaction between adsorbed molecules on a metal site [18]. For example, Yang et al. [65] proposed that the C,H, molecules are first attracted by the Brgnsted acid sites in Ag/ZSM-5, followed by О· attacked the adsorbed ethylene species. Then the C-C bond was broken, and formed formaldehyde species, which reacted with O· species to form carbonic acid species. Finally, carbonic acid species decomposed into CO, and H,O. Similarly, on the Pt@S-1 catalyst, acetone molecules are first adsorbed on the active sites of the catalyst, and then oxidized to acetic acid and formic acid under the action of active oxygen, and then converted into bicarbonate species and finally decomposed into CO, and H,O [66]. In addition, Peng et al. [67] found that the degradation of propane on Ru@S-1 belongs to the MvK mechanism. Propane molecules are adsorbed in the zeolite shell. The hydroxyl groups (Si-OH from zeolite framework) on the zeolite surface provide active oxygen for the activation of propane, as shown in Fig. 4d, finally generate CO, and H,O, and the Si-OH was regenerated after water produced. It is further confirmed that the plausible reaction process over Ru@S-1 follows the MvK mechanism. The reaction order in VOC depends on the nucleophilic character of the organic molecule. Generally, a negative order is observed in unsaturated hydrocarbons due to their strong adsorption on the Pt/Pd surface through 7c-bonds and backdonation from the metal to the 7r·-hydrocarbon orbitals [18].

Due to its high chemically inertness, Au-based catalysts typically exhibit poor catalytic activity and tend to remove VOCs at higher temperatures (190-400 °C) in comparison to Pt- and Pd-based catalysts [68]. Nonetheless, Au-based catalysts effectively hinder carbon buildup, a by-product of incomplete combustion during the catalytic process, thereby reducing catalyst deactivation [17]. Ag-based catalysts can also be applied in VOC catalysis, which will be relatively cheaper in preparation compared to other noble metals, and Ag can have a synergistic effect with metal oxide carriers to promote the formation of oxygen-active species in the catalytic oxidation of VOCs [69], thus improving the catalytic activity. Although both Au and Ag-based catalysts have certain advantages, their weaker metal-O bonds and lower catalytic activity at low temperatures significantly limit the practicality of these two metal catalysts compared to the widely used Pd/Pt-based catalysts in VOCs catalytic oxidation.

Pd is extensively utilized in the catalytic removal of industrial VOCs, especially some short-chain hydrocarbons or aldehydes and alcohols, owing to its distinctive arrangement and exceptional stability [8]. The active forms of Pd involved in the catalytic oxidation of VOCs are Ра° and PdO, but there is still a debate regarding which valence state plays a significant role. Some researchers argue that PdO-type catalysts are more suitable for VOCs activation because the С-Н bond energy barrier for activation of the PdO phase is lower than that of the metal Pd [70], another scholar suggested that the coexistence of PdO and metal Pd plays a stronger role in promoting VOCs activation [71]. Generally, it become challenging to differentiable the state of Pd since, during the high-temperature catalytic combustion of VOCs, Pd is susceptible to oxidation/reduction transformations that may affect the catalytic activity of VOC oxidation, leading to confusion about the effects of the Pd phase. In general, the factors influencing the catalytic activity of Pd-based catalysts loaded with VOCs include the particle size of Pd, the chemical state of Pd, as well as the type and acidity of the support material, among others. Based on the acidity strength of the support materials, the accelerated transformation of Pd° to Ра?! can enhance the catalytic oxidation of VOCs [72]. Moreover, the acidity of the supports plays a crucial role in catalysts with high Pd dispersion and has been identified as beneficial in promoting the catalytic reaction [73,74]. Additionally, the size of Pd nanoparticles also impacts the catalytic activity. A study conducted by Giraudon et al. [75] discovered that reducing the size of Pd nanoparticles increases the interface between Pd and the carrier material, enabling faster replenishment of oxygen vacancies and better dispersion, ultimately providing a larger pool of mobile oxygen.

Pt-based catalysts show better catalytic combustion activity for long-chain hydrocarbons (Pentane and above) [76] and aromatics and have better low-temperature activity than Pdbased catalysts, with better catalytic performance for benzenes (BTEX) in the range of 150-300 °C [77]. Therefore, Pt is more often used as an active component in the catalytic oxidation of VOCs than Pd. Numerous studies have shown that the active sites of Pt/zeolite catalysts applied to the catalytic oxidation of VOCs are Pt" clusters distributed on the zeolite surface. To effectively adsorb/activate O, and VOC molecules, the formation of high-content, highly dispersed active Pt sites on zeolites is key. For example, Luo et al. [78] showed that the appropriate acidity on the zeolite surface not only inhibited Pt oxidation to maintain the Pt" content but also promoted the reducibility of Pt"· ions. Zhu et al. [79] reported that doping of elements such as W also effectively inhibited Pt oxidation to increase the Pt" content, which in turn effectively improved the catalytic activity. In addition, the particle size of Pt particles is also an important influencing factor, and Pt particles around 1.9 nm are considered to possess the best catalytic activity with both good Pt dispersion and excellent Pt" content [80]. Zeolite-loaded Pt has also been used for the degradation of CVOCs, where the C-C1 bond is cleaved at the acidic site and the resulting intermediate is deeply oxidized at the active Pt site. For example, Taralunga et al. reported that the catalytic oxidation performance of Pt/HFAU on chlorobenzene was better than that of Pt/SiO, and Pt/Al,Os. Pinard et al. [81] studied the influence of acidity and alkalinity on the surface of zeolite support on the catalytic oxidation of dichloromethane (DCM) by Pt/NaX and Pt/NaY. Although Pt-based catalysts are known to be super active in VOC oxidation, the high bonding energy of chlorine after dissociation on the surface of the Pt-based catalyst will reduce its catalytic activity and result in the chlorination of the skeleton. Wang et al. [82] loaded Pt with high catalytic activity and Ru with strong chlorine removal ability on the H-ZSM-5 zeolite with regular channels and strong acidity, and the Pt-Ru-HZSM-5 catalyst showed great chlorobenzene (CB) catalytic activity and high selectivity for less toxic products (CO, and HCI), scarce formation of chlorinated byproduct (DCB) and good stability. In addition, Su used Co doping to prepare Pt-Co/HZSM-5 catalyst [83]. In the case of adding only trace Pt (0.01 wt%), dichloromethane (DCM) Toox is 249 °C, which is 67 °C lower than 0.01 wt% Pt-HZSM-5. It was found that the anchoring of Pt atoms by Co resulted in the monatomic dispersion of Pt, and the high dispersion of Pt increased the ratio of oxygen vacancy on the surface of Co, and improved the selectivity of dechlorination byproduct (CH;Cl), thus effectively alleviating Pt poisoning.

2.3. Comparison of active species

Despite being precious metal-loaded materials, the requirements for the precious metal active components used vary due to different target reactants and application scenarios and different principles of action. The following is a brief analysis of the differences between the two, taking Pd-PNA and Pt-VOCs catalysts, which are the most widely used among PNA and VOC purification materials, as examples. It is summarized in Table 3.

Firstly, from the perspective of active species, zeolitesbased PNA has identified Pd as the most efficient active component due to its moderate binding strength to NO;. This allows for the release of previously stored NO, within a suitable temperature range, resulting in good low-temperature NO, adsorption capacity [13]. For VOC catalytic combustion, Pt-based catalysts have better catalytic activity and stability and can be adapted to most VOCs (aliphatic hydrocarbons, oxygenated VOCs, aromatics, etc.) [12]. Secondly, in terms of active species valence, superior PNA materials require active sites that efficiently store NO, at low temperatures and release it in large quantities at temperatures suitable for subsequent SCR (< 350 °C). Isolated Pd?" acts as the predominant NO, adsorption site, forming nitrosyl complexes by directly coordinating with NO. These complexes are not only directly releasable at appropriate temperatures but also highly waterresistant. Differently, on VOC catalysts, as shown in Fig. 4, the key to the catalytic oxidation reaction of VOCs lies in the formation of activated O, and PS with empty d orbitals can adsorb/activate O, and VOCs molecules with high efficiency and promote the rapid progress of the catalytic oxidation reaction of VOCs. Consistently, acidic sites play an important role in the adsorption of reactive molecules on both materials. Finally, in terms of the requirements for the distribution of active sites, for PNA, Ра?" is usually encapsulated inside the micropores of the zeolite to prevent free Ра?! from agglomerating into inactive РАО clusters. For VOC catalysts, P is usually distributed on the surface of zeolite due to the stronger interaction of zero-valent Pt with the carrier and the generally larger diameter of VOC molecules, which makes it difficult to enter into the micropores. However, regardless of the material, a high dispersion of active metals and a high percentage of active species are required to be distributed on the zeolite. Therefore, the formation of high proportion and high dispersion of Pd"· and Pt? is the key to the efficient adsorption of МО, by Pd/zeolite and catalytic oxidation of VOC by Pt/ zeolite.

3. Progress in active site construction for noble metal/ zeolite-based PNA and VOC catalysts

As was concluded above the construction of highly active and dispersed Pd"· and P on zeolite supports is crucial for obtaining excellent catalysts for PNA and VOCs catalysts. For materials like noble metal/zeolite composites, factors such as the precursor of noble metals, structural properties of the support (e.g., topology, pore size, Si/Al ratio, acidity, co-cations), as well as the interaction between noble metals and supports (including introduction methods and post-treatment techniques) need to be considered. Therefore, in this section, we will summarize and discuss the influencing factors on PNA and VOC catalysts separately.

3.1. Construction of active sites in PNA

3.1.1. Noble metal precursors

Pd-based precursor salts commonly used include РаМОз, Pd(NH;)4Cl,, [Pd(NH3)4](NO3)», etc. The effect of precursor salt selection on fresh Pd-based catalysts is not yet clearly established, and some relevant current studies are briefly discussed here. Numerous experiments have shown that the Pd ion content and dispersion on zeolites are significantly increased when NHz-containing precursors are used for loading. The sample prepared using Pd(NH3)4Cl, as the precursor forms a very small amount of inactive Pd clusters on the outer surface of the zeolite, and most of the Pd enters the zeolite micropores in the form of isolated Pd?+ (Fig. 5a) [97]. However, since the precursor contains Cl" ions, it may cause potential chlorine poisoning hazards to the precious metal Pd. Recently, researchers have used [Pd(NH3)4](NO3); instead of Pd(NH3),4Cl, as the precursor to prepare Pd/zeolite. During the ion exchange process, it is difficult for the negatively charged Pd ion complex of the Pd(NO;), solution to diffuse into the similarly negatively charged zeolite pores, which hinders the ion exchange process and leads to the accumulation of a large number of precursors on the outer surface of the zeolite. Therefore, when using PdNO; as the precursor, most Pd will distribute on the outer surface of the zeolite in the form of Pd clusters (Fig. 5b), which greatly reduces the NO, adsorption activity of Pd/zeolite [97]. The addition of the NH; ligand allows Pd ions to form positively charged [Pd(NH3)4]·· and smoothly enter the zeolite pores to undergo ion exchange with H· [98].

3.1.2. Zeolite structural properties

Zeolites with different pore sizes (8 MR, 10 MR, 12 MR) are widely used in the research of PNA supports, among which CHA, MFI and BEA are the most studied. Their frame images are shown in Fig. 6.

The unique topology and pore structure, which affect the content and dispersion of Pd"· on the carrier by influencing the size of pores, specific surface area, and cage of the zeolite, Will also bring about differences in the hydrothermal stability of Pd/zeolite adsorbents. Firstly, the pore size affects the distribution of Pd"· in zeolite support. During the synthesis of Pd zeolite using conventional methods of ion exchange, it is observed that in Beta and ZSM-5 zeolites, the majority of Pd is distributed within the channels of the zeolite as individual Pd cations, while the remaining portion is dispersed on the outer surface of the zeolite as PdO, clusters and particles. In contrast, in SSZ-13 with CHA topology and smaller pore size (-0.38 nm), the majority of Pd species are highly dispersed as extremely thin PdO, clusters (mainly PdO, clusters) on the outer surface [37]. This is primarily due to the hindrance of ion exchange between Pd precursors and zeolites caused by the small pores of SSZ-13 [35], resulting in the lowest density of isolated Pd"· ions on SSZ-13 zeolites, finally leading to small NO, storage capacity. Both Chen et al. [14] and Zheng et al. [37] got the similar conclusion that the larger the pore size, the more Pd precursors entering the zeolite channels, the more Pd ions formed by ion exchange, and the better the NO, adsorption activity. Additionally, zeolite pore size will also bring about differences in Pd ion mobility. After undergoing hydrothermal treatment, it has been reported that Pd ions in Pd/SSZ-13 display reduced mobility compared to other Pd/ Zeolites with larger pore openings (e.g., Pd/ZSM-5 and Ра/ BEA) because the narrow pore openings of SSZ-13 restrict the movement of Pd ions [99]. Although the loading process of SSZ-13 results in a low formation of Pd"· density, the activity of medium and large pore size Pd/zeolite catalysts (В zeolite, modernite, and ZSM-5) is significantly reduced after undergoing HTA treatment. The activation of the PNA ability of the small-pore Pd/SSZ-13 catalyst is observed post HTA treatment. He" s group [100] prepared Pd-SSZ-13 with 750 °C thermal (TA) and hydrothermal aging treatments (HTA). The effect of post-treatment on the migration of Pd species on zeolite was analyzed. As shown in Fig. 7a after TA and HTA, PdO was redispersed into Pd", Which resulted in enhanced NO, adsorption performance. Part of Pd"· adsorbed NO at low temperature (< 300 ·C) and stored as Pd"·-NO. Part of Pd?· is combined with OH- at the Brgnsted acid site to form Pd[OH]·, which can effectively adsorb NO at high temperature (300-450 °C) (Fig. 7b). Furthermore, due to the hydrolysis of Si-O-Al, hydrothermal aging will accelerate the deal of zeolite, so compared with Pd-HTA, thermal treatment can better realize the high dispersion of Pd and reduce skeleton dealuminization, Thus, in terms of long-term durability for practical applications, choosing the Pd/SSZ-13 catalyst would be more favorable [14,99,101]. The unique structures of smallpore zeolites like AFI, CHA, and FER, also contribute to differences in hydrothermal resistance and stability. In the experiments conducted by Shan et al. [40,102], the AEI zeolite features a three-dimensional but tortuous pore channel structure. This structure accelerates Pd dispersion at 750 °C and inhibits Pd aggregation at 800 °C when subjected to hydrothermal aging. In the case of Pd/CHA, there is a slight increase in Pd dispersion at 750 °C, but significant Pd aggregation at 800 °C due to its straight and unhindered three-dimensional pore structure [40]. Furthermore, recent research suggests that Pd-FER shows a promised as a PNA material [103]. Khivantsev et al. [104] compared the PNA storage and stability of Pd-SSZ-13 and Pd-FER under simulated high-concentration CO exhaust gas conditions and found that Pd-FER exhibits better hydrothermal stability than Pd-SSZ-13. This improved stability can be attributed to the thermal migration of Pd ions to specific positions within the FER micropores, resulting in the formation of PdII/2Al. In the presence of 10% H,O, PdII/2A1 displays resistance to hydrothermal aging up to 800 °C.

Secondly, the Si/Al ratio of the framework plays a crucial role in determining the NOx adsorption capacity and stability of PNA, primarily by impacting the distribution of Pd". When comparing Pd/SSZ-13 samples with varying Si/Al ratios, it was found that the NO, storage performance of Pd/ SSZ-13 samples with lower Si/Al ratios was significantly better than that of other samples [98], in the PNA test, with the increase of Si/Al ratio (Si/Al = 6, 12, 30), NO, storage efficiency radially decreases from 94 pmol g ' to 81.8 ито! gü Correspondingly, NO,/Pd decreases from 1 to 0.87 and 0.3. It is well-accepted that ion-exchanged Pd ions are mainly anchored to charge-compensated Al sites on the zeolite, so the higher the Al content (the lower the Si/Al), the more ion sites can be exchanged and the higher the density of Pd"· dispersed on the zeolite [104,105]. However, the hydrothermal stability of the zeolite is inevitably reduced as the Al content increases due to the easier dealumination of the framework [106]. Additionally, Brgnsted acid sites (BASs, namely, the -Al(OH)-Simoieties on zeolite framework) which are more susceptible to H,O, thus limiting the NO, adsorption, will greatly increase with Si/Al ratio decreasing [107,108]. Therefore, it is necessary to consider various factors when adjusting the silica-alumina ratio, taking into account of both performance and stability. It has been well known that the most effective active site on PNA to capture NO, from the vehicle exhaust is Pd·", which could form only at paired framework Al sites to maintain charge balance in zeolite. Thus, the proportion of paired Al sites should be maximized while optimizing the Si/Al ratio to enable the highly dispersed encapsulation of Pd ions within the zeolite framework. In a study conducted by Theis' group [109], they prepared three Pd/H-CHA samples with similar Pd loadings but different concentrations of paired Al sites (53.0%, 10.8%, and 6.5%) at nearly fixed Si/Al ratios to investigate the effect of Al pair content on NO, adsorption performance (Fig. 8). The experimental results demonstrated that in the two samples with higher concentrations of paired Al sites (53% and 10.8% of Al paired), the Pd species existed almost exclusively as isolated Pd cations, while a certain amount of PdO clusters were found in the other sample (6.5% of Al paired), and the NO, storage rate was the lowest in this sample. Furthermore, the sample with 53.0% paired Al sites also exhibited good thermal durability and anti-deactivation performance in the presence of CO. This behavior was attributed to the more effective interaction between CO and Pd at the paired aluminum sites, leading to the formation of a Pd(CO)(NO)·· complex [110].

Recently, Pd -loaded Al-rich Beta zeolites have demonstrated excellent МО, adsorption properties and have been successfully utilized in PNAs [111]. Compared to conventional Beta zeolites, Al-rich Beta zeolites contain a higher number of Al pairs sites [111,112]. During the ion exchange process for Pd loading, a significant amount of highly active Pd" is generated and stabilized at these Al pairs sites. By Xiao's group [112], Beta zeolite with Si/Al = 4 was prepared using a organotemplate-free method. The resulting material exhibited outstanding low-temperature NO storage performance (NPR = 0.92 pmol NO gh, which was maintained even after hydrothermal aging at 750 °C, showing a certain NO, storage capacity (NPR = 0.58 pmol NO g "). The absence of organic templates in the preparation of Al-rich Beta zeolites, coupled with their high performance and cost-effectiveness, positions them as promising supports for PNAs. On the contrary, it has been suggested that modified the support to remove Al can improve the long-term stability and cycling performance of PNA. Shen found that [113] when Beta dealumination with oxalic acid, non-skeleton Al and unstable skeleton Al at T;¿-Ty sites were mainly removed, and the proportion of Al at T¡-T> sites with strong acid resistance and high stability increased, and Pd species exchanged with OH" at the attachment of T¡-T> Al site, forming ultra-stable Pd", Which shows excellent long-term stability during the NO, adsorption process. Compared with conventional Pd/Beta, the Pd/Beta of dealumination still retains 56% NO, adsorption performance under the dual action of hydrothermal aging at 850 °C and reducing gas, showing excellent NO, storage stability in 10 cycles [114]. However, due to partial removal of Al, the Si/Al ratio increases, the total Pd·· content of the exchange decreases, and the total NO, adsorption is inhibited [114].

Thirdly, it has been discovered that zeolites can incorporate other components, such as alkaline earth metals, rare earth metals, and transition metals. The introduction of these nonframework cations serves to protect the framework Al structure, stabilize the active Pd sites, and improve the hydrothermal stability of the material [115]. For instance, in an experiment conducted by Cai et al. [116], Mg"? was introduced into the Pd/SSZ-13 material. The Mg"? ions were preferentially anchored at the Al counter site and exhibited strong affinity with SSZ-13 even under high-temperature aging (HTA) conditions of 850 °C. This interaction reduced framework dealumination and effectively enhanced the NO, storage capacity of Pd/SSZ-13 at 850 °C. Metal doping not only improves the hydrothermal stability of Pd/zeolite materials but also reduces the amount of NO, desorption at temperatures below 200 °C. This promotes a better match between Pd/ zeolite and subsequent selective catalytic reduction (SCR) treatment systems in practical applications, thereby enhancing their value. Lee et al. [117] conducted experiments that demonstrated how the incorporation of Co into Pd/BEA molecular sieves stabilizes the active Pd sites, resulting in higher МО, desorption capacity at temperatures above 200 °C. Density functional theory calculations revealed that Co and Pd form direct bonding interactions, thereby reducing the migration and agglomeration of Pd species at high temperatures. Similarly, the doping of the rare earth metal La also achieved optimization effects. However, Ilmasani et al. [60] found that the doping of other metals partially displaces the active Pd sites, leading to the agglomeration of Pd species and the formation of PdO with low МО, adsorption activity. This results in a 25% reduction in the NO, adsorption capacity.

3.1.3. Metal introduction support

Common methods of loading Pd onto zeolite include Impregnation and Топ exchange methods. The ion exchange method stands out as a widely utilized strategy to confine metal species within zeolites, particularly at ion exchange sites. This method capitalizes on the negatively charged framework of aluminosilicate zeolites, with cations (Nat, К", NHJ, and H") outside the framework located in the channels of the zeolite to achieve charge balance. These chargebalanced cations can move freely in the aqueous solution of the loaded cations and exchange with other metal cations [118], which are mainly divided into aqueous ion exchange and solid-state ion exchange. Solid-state ion exchange (SSIE), a simplified process that does not involve water, is considered an alternative to overcome the problems of solvent-based methods and has been explored several times in recent years. Ryou et al. [35] first used the SSIE method to load Pd (mixing and grinding precursor and support and then performing ion exchange at high temperature). However, during the hightemperature preparation process, the PdCl;, intermediate with larger particle size is formed by the aggregation of the Pd precursor PdCl,, resulting in uneven distribution of Pd particles on the support and poor low-temperature NO, adsorption performance [35]. Therefore, Liu et al. [119] used PdO as a precursor to prepare Pd"·-rich 5 wt% Pd-SAPO-34 at 800 °C and showed good PNA performance (32.12 ито! g "). Similarly, Shimizu's group [120] directly used Pd black as the precursor, and successfully converted a large amount of palladium metal on the surface of CHA-type zeolite into Pd" ions at the zeolite anion position under NO flow conditions at 600 °C, and the Pd loading amount was as high as 76%. Compared with the liquid-phase ion exchange method, the solid-phase ion exchange method could avoid the liquid-phase ion exchange that may produce wastewater and achieve certain results in the loading of noble metal cations. However, solidphase ion exchange requires a higher energy input [121], Which has the potential to damage the zeolite framework. Additionally, solid-phase ion exchange is characterized by slow mass transfer between solid phases and low ion exchange efficiency [35,119,120]. As a result, its practical applicability is significantly lower compared to liquid-phase ion exchange.

Therefore, liquid-phase ion exchange has been viewed as the most common Pd-zeolite construction strategy with its excellent Pd species dispersion, effective Ра?" site construction ability as well as low energy consumption. However, it still has significant limitations. The most important thing is the poor metal loading rate and low metal content of the Pdzeolite adsorbent obtained by the ion exchange method. Particularly, when loading Pd on some neutral skeletal zeolites (e.g. silicate zeolites) or high-silica zeolites, the ion exchange method is not applicable because there are very few or even no exchangeable acidic Al sites on the skeleton. Using ammonium ion exchange zeolite as a support (e.g., NH4-SSZ-13) has been reported to effectively enhance the uptake rate of Ра? during ion exchange. Generally, Pd ions were exchanged with protons of H-zeolites following the reactions of Ра?! +2Z H'04Z PdZ +2H· (1), this reaction is reversible. Thus, only a small amount of Pd?· can be successfully exchanged to the ion exchange site, and most Pd"· fail in the competition of zeolite protons. By country, using NHs-zeolite with low Si/Al ratio as the support, and Pd(NO3), or [Pd(NH3)4](NO4)» containing nitrate as the metal precursor, obtained Pd/SSZ-13 with Ра?! ion dispersion of 100% under Pd relative load of 1.9 wt%. This is attributed to the thermal decomposition of ammonium nitrate species at 200 °C consumes NHJ (Ра?! + 2Z-NH} +Z2-Pd?· + 2NH}) (2), which facilitates a shift of the reaction equilibrium in eq1 to the right side, promoting the formation of dispersed Pd?" species. Besides, free МНД combined with Pd ions can form [Pd(NH3),1°" complex intermediate, which has high fluidity and effectively promotes the diffusion of Pd ions [98].

Impregnation is a simple and mature method for obtaining Pd-zeolite catalysts. The dehydrated zeolite is thoroughly mixed with a specific quantity of metal precursor solution, the metal precursor enters the micropores of the zeolite through capillary force and will be distributed inside the zeolite after drying and calcination process, during which the water will be completely removed while the precursors will be decomposed/ converted to various metal species. Metal loading can be better controlled when using the impregnation method, ensuring that all Pd precursors are retained in the final Pd-zeolite product. However, it is important to note that these methods might result in a larger fraction of PdO, particles rather than Pd ions. This is because, by the impregnation method, the metal species position cannot be controlled and is prone to forming large-sized metal nanoparticles in the subsequent heat treatment. Nonetheless, recent studies have highlighted the advantages of combining the impregnation method with some post-processing measures to synthesize Pd-zeolites with of high-loading and a predominant presence of Pd ions. Royu et al. [35] reported that the fresh Pd/SSZ-13 catalyst prepared through the impregnation method hardly adsorbed NO due to the fact that Pd was mainly present as PdO. However, after hydrothermal treatment, a large amount of PdO was redispersed as Pd··, which effectively improved the performance of the adsorbent. Shan et al. [40] obtained the same results for small pore zeolites (e.g., LTA, CHA, AEI) with different pore structures also loaded with Pd by impregnation method and subjected to hydrothermal treatment, where a large amount of Pd"· was dispersed into the pore cages of small pore zeolites after hydrothermal treatment and the NO adsorption performance was substantially improved. However, it should be noted that when the deep hydrothermal treatment (800 °C) of the adsorbent was continued, it would lead to a decrease in Pd"· content due to the reduction of Al exchange sites brought about by the dealumination.

3.2. Construction of active sites in VOC catalysts

3.2.1. Noble metal precursors

Previous studies have shown that the types of noble metal precursors affect the performance of the prepared catalysts [122-124]. The following takes the active metal Pt, which is the most used in VOCs, as an example to briefly introduce the influence of Pt precursor forms on the load of Pt on zeolite. The commonly used precursors of supported Pt-based catalysts include Pt(NH3)4(NO3),, H>PtClc, Pt(NH3)4Cl>, etc. It has been shown that the ligand species, charge state, and molecular size of the Pt precursor all have some influence on the loading of Pt on zeolite. Anionic complexes such as РС, due to their negative charge, have weak electrostatic forces with the equally negatively charged zeolite, and are easy to load on the zeolite surface to form larger platinum particles, while cationic complexes such as [Pt(NH3)41?·, will have strong interactions with the acid center of zeolite, thus forming highly dispersed platinum nanoparticles anchored on the acid sites [122,125]. Quinones et al. [122] prepared Pt/ MOR zeolite catalysts using two precursors of H,PtClg and Pt(NH3)4(NO3)2, respectively. Compared with the positively charged Pt(NH3)4(NOj3),, the negatively charged H,PtClg precursor diffused within the pores of the zeolite with great difficulty, and thus Pt was mostly loaded on the surface of zeolite for the former precursor. Similar results were also obtained by Oenema et al. [126]. By using Y/y-A1,0; composite as the support, the anionic [PtCl5]· (aq) complexes generated from H,PtClg-6H,0O dissolved in water will be loaded on the outer surface of positively charged y-Al,O3 by electrostatic adsorption, whereas cationic [Pt(NH3)1]"· (aq) complexes generated from Pt(NH3)4(NOj3), precursor dissolved in water will be loaded within negatively charged Y zeolite crystals by ion-exchange of the Pt cations. Another argument suggests that the dispersion of Pt(IV) precursors With a spatial octahedral structure on zeolite carriers is higher than that of Pt(IT) precursors with a planar square structure due to the spatial site-barrier effect [127], meaning the use of H-PtCl5 instead of Pt(NH3)7 -based salts as a noble metal precursor was better dispersed and showed higher catalytic activity. However, it should be noted that the use of Cl-containing precursors may affect the catalytic activity of VOCs. Even after roasting at 600 °C, CI will still remain on the catalyst surface [128], but at low load, the influence of the presence of Cl on the catalytic activity is enough to be ignored [125]. Recent studies have found that different ligands can selectively control the size of noble metal NPs and their position on the zeolite skeleton [129-131]. Di et al. used different organic ligands to stabilize the Pd precursor system to prepare Pd@S-1 catalyst. and the results showed that Pdligand complex with diverse ligands shows different spatial hindrances, and enter different pore channels by electrostatic or van der Waals interactions during the S-1 synthesis process (as shown in Fig. 9) [132]. Among them, the chelate formed by the complexation of ethylene diamine with more N atoms, short carbon chain, small branch chain and bidentate coordination with Pd·· shows the least steric hindrance, resulting in Pd mainly located in the 5 MR channel of S-1. Thus, the growth of Pd clusters was limited and their dispersion was promoted, and the conversion efficiency of formaldehyde reached 100% at room temperature. In short, the structure of the precursor, the valence state of the complex, and the spatial structure will affect the size, location, and distribution of Pt nanoparticles, so it is necessary to comprehensively consider the optimal use when applying different VOC catalytic oxidation.

3.2.2. Zeolite structural properties

As the core component of noble metal-loaded catalysts, zeolitic structural properties (i.e., pore size, structure, acidity, and hydrophobicity) have been proved too closely affect VOC catalytic reaction because of their significant effect on the ability of VOCs diffusion and adsorption, which are both important stages for the reaction process. Firstly, the adsorption of VOCs by zeolites is mainly dependent on their open-skeleton structure, and zeolites with larger pore sizes can effectively reduce the spatial site resistance and increase the diffusion rate of VOCs. In the study of the relationship between toluene adsorption and zeolite pore size [133], MOR zeolite showed superior toluene adsorption performance (О. = 1.7 mol kg ") than MFI (О. = 0.75 mol kg ') and FAU (О. = 0.7 mol kg") due to higher specific surface area and larger pore size (~0.56 nm). Similar results have also been reported by Cosseron et al. [134]. As shown in the Fig. 10 the hexane adsorption capacity of CHA zeolite with smaller pore size was significantly lower than the other zeolites with larger pore size (MFI (1.28 mol kg ') > BEA (1.23 mol kg ') > STT (1.13 mol kg) > CHA (0.18 mol kg). In addition, the structural morphology of zeolite can affect the mass transfer of some macromolecular reaction materials within the zeolite and the potential to reach the internal metal active sites. In Chen's experiment [135], three different morphologies of S-1 zeolite were synthesized (plate, brick, and spherical). Due to the short b-axis and well-grown single-crystal structure of plate-like zeolite, it exhibits lower diffusion resistance for toluene molecules and therefore has the highest reaction rate constant. Secondly, it has been well acknowledged that the VOC catalytic ability is also greatly influenced by the acidity of the catalyst surface because surface acidity is crucial for activating the adsorption of VOC molecules, breaking С-Н bonds, and forming coking. According to Yang et al.'s report [86,87], the Bronsted acid site was viewed as the active site for the catalytic oxidation of ethylene on the Pt/ZSM-5 catalyst. Further studies by Gu et al. [136] demonstrate a direct correlation between the number of strong acid sites and the adsorption capacity of toluene. Alejandro's [137] experiments confirm that the Brgnsted acid site on zeolite surfaces can interact with weakly basic aromatic hydrocarbons, such as benzene, toluene, and xylene. The Lewis acid site can create Lewis acid-base admixtures with these hydrocarbons [138]. Furthermore, acid sites can break down C-H and C-CI bonds, facilitate the separation of VOC molecules, and safeguard the catalyst from harmful S and Cl ions [139]. However, an excessive degree of acidity can hinder desorption, leading to decreased efficacy, heightened secondary product production, promotion of carbon buildup, and catalyst deactivation [139].

It is crucial to note that the support's structural properties also play a vital role in the formation/dispersion of active metal sites during catalyst construction, which finally determines the catalytic activity of catalysts. For example, as Ytype zeolite has a larger specific surface area and pore volume compared to ZSM-5, a smaller particle size and more uniform dispersion of surface-loaded platinum was observed in the former, resulting in its better catalytic oxidizing activity for nhexane [140]. Liu employed a controllable desilication treatment on ZSM-22 using a NaOH solution with the addition of CTAB, precisely forming small mesopores within the diameter range of 2.9-9.3 nm [141]. This process not only retained the original framework but also exposed accessible Brgnsted acid sites, providing limited mesoporous space and defect sites for highly dispersed and stable anchoring of Pt particles. Therefore, research has focused on micro-mesoporous zeolite-supported Pt catalysts for their ability to increase surface area and promote the highly dispersed load of the active metal, potentially overcoming mass transfer resistance in microporous zeolite [142,143]. Wang et al. [144] obtained Pt/ZSM-5 catalyst with ultrafine Pt particles and abundant micro mesoporous structure, which exhibited good degradation activity in the catalytic oxidation of a variety of VOCs such as hexane, ethyl acetate, acetonitrile, and dichloroethane, especially for the oxidation of hexane, where the Too% of PYZSM-5 (0.1) was only 142 °C. In addition, hierarchical zeolites can effectively improve the lifespan of catalysts. As shown in Fig. 11а, compared to traditional Pt-R/Beta catalysts, Pt-R/Beta-H with a micro-mesoporous structure maintains 100% toluene conversion rate and CO, selectivity after 10 h of reaction, while Pt-R/Beta catalysts start to significantly decline after 6 h [145]. Moreover, Pt-R/Beta exhibits poorer resistance to coking compared to Pt-R/Beta-H, showing strong coking during the reaction process. Liu et al. [146] prepared a series of Pd/transition metal oxide-functionalized single crystals with b-axis aligned mesoporous channels (Pd-La/ZSM-5-OM), which retained an 81.4% benzene conversion rate even after a reaction time of 13 h (Fig. 11b), while Pd-La/ZSM-5 without the formation of micro-mesoporous structures only achieved a benzene conversion rate of 20.2%. This is attributed to the excellent metal dispersion and anti-aggregation properties brought by the novel b-axis aligned mesoporous channels. Similar results have also been reported for layered MOR zeolite-supported Pt in toluene oxidation reactions [147].

One of the important reasons why zeolite is widely used as VOCs catalyst support is its adjustable acidity and wettability. Both properties are related to the Si/Al ratio of the zeolite framework. First of all, the addition of Al causes the zeolite skeleton to be negatively charged and generate Brgnsted acid centers. Therefore, the lower the silica-aluminum ratio of the zeolite, the higher the acidity. Acidity has a strong regulatory effect on the valence, position and dispersion of foreign active sites [148]. The acid site exhibits an ability to withdraw electron; the electron-withdrawing ability becomes stronger as the acidity increases, resulting in a stronger attraction towards Pt precursors. This promotes the separation of Pt during the reduction process and results in a more uniform distribution of Pt particle size [149]. Furthermore, the interaction between Al and Pt is stronger in comparison to Si-Pt, which enhance the anchoring of Pt active species. Slow down Pt agglomeration, leading to an improved Pt dispersity [149]. Both Lou [73] and Jableopolska's [74] experiments observed that the Brgnsted acid site present on the zeolite surface plays a significant role in promoting the formation of active metal species PdO and acting as an anchor site, leading to the high dispersion of PdO in zeolite stably. Xiao's group [150] achieved complete oxidation of formaldehyde at room temperature using Al-rich Beta zeolite (Si/Al = 4). The rich Al species in the zeolite skeleton not only increases the acidic site density, but also enhances the interaction between the positively charged Pt precursor and the negatively charged zeolite skeleton, making the Pt nanoparticles highly dispersed. Secondly, since the addition of Al forms a negatively charged zeolite skeleton, there are cations compensating for the charge in the skeleton, and these cations act as polar points to make the zeolite hydrophilic, so the higher the Si/Al ratio, the better the hydrophobicity of the zeolite. VOC oxidation as a typical aqueous reaction (M + О, - CO, + H,0), the hydrophobicity of the catalyst plays a crucial role in the desorption and transfer of water products. According to Zhang's report [94], hydrophobic silica-based Beta zeolite is used as a support and exhibits excellent catalytic performance for formaldehyde at an extremely low Pt loading (0.2 wt%). Even under low temperature conditions (-20 °C), this catalyst can completely oxidize formaldehyde to CO,. This outstanding performance is attributed to the rapid desorption of water products on hydrophobic Pt/Beta-Si and the improvement in intermediate conversion rate, which tilts the balance of formaldehyde oxidation reaction towards product formation direction, significantly enhancing reaction activity and CO, selectivity. In addition to affecting the anchoring and dispersion of noble metals on the support, the structural properties of zeolite support will also bring differences in catalytic reaction mechanism and path. The catalytic oxidation of VOC molecules can be effectively improved by changing the acidity and hydrophilicity of the carrier itself to accelerate the generation and transformation of intermediate products or shorten the reaction path. According to Li's report [151], on low-silica Pt/ Beta, toluene is first chemisorbed on the Pt/Beta catalyst in the form of benzyl alcohol. Under the action of hydroxyl groups and other reactive oxygen species, benzyl alcohol is further oxidized into benzaldehyde and benzoic acid. The benzene ring is then opened to generate CO, and H,O. In the process, by-products such as benzene, CO, and benzaldehyde/acid are produced (Fig. 12). On high-silicon Pt/Beta, the presence of Pt? effectively activates O> to generate and supplement reactive oxygen species, toluene can be rapidly oxidized into CO, and H,O, with almost no by-products produced in the process, and the catalytic activity is significantly enhanced. Another example is that Li et al. [152] designed and developed a tandem bifunctional ZSM-5-Agnp/SAB-15 catalyst with two functionally complementary active sites. The acidic sites of ZSM-5 convert formaldehyde into methyl formate, which then diffuses to the surface of Agnp/SAB-15 for complete oxidation. Compared with the dioxymethyl-formate oxidation path on the surface of Agnp/SAB-15 alone, the tandem bifunctional catalyst significantly reduces the temperature required for formaldehyde oxidation by changing the reaction path and can achieve complete oxidation at 65 °C.

The formation of noble metal active species is also influenced by the doping of heteroatoms in the zeolite skeleton. By introducing electrophilic metal element additives such as V, W, Mo, and Nb, the oxidation of Pt to a high-valent state becomes more difficult, thereby enhancing the oxidation resistance and catalytic activity of the catalyst. As reported by zhu et al. [79], the addition of W to Pt/ZSM-5 catalysts increases the promotion of propane oxidation by facilitating the formation of Pt". Liao et al. [153] obtained the same effect by co-impregnating Mo, and the catalyst showed better stability compared with undoped Mo materials. In addition to single atoms, the effect of metal oxide doping into the zeolite has also been investigated. According to Zhao et al. [154], the introduction of NbO, created new acidic sites on the Pt/Al,O; surface, thus promoting the formation and dispersion of Pt species. Furthermore, alkali metal doping influences the dispersion of active species on zeolites due to the difference in the electronegativity. As the electronegativity of the cations in the catalysts decreases, the transfer of electrons between the zeolite skeleton and Pt particles becomes more pronounced, which is more conducive to the formation of the active component Pt'. Different Pt/ZSM-5 catalysts prepared by Chen et al. using ZSM-5 zeolites with varying compensating cations (H·, Na·, K·, Cs") as supports, demonstrated distinct catalytic performances for toluene. Notably, Pt/KZSM-5 and Pt/CsZSM-5 catalysts exhibited higher catalytic activity compared to Pt/HZSM-5.

3.2.3. Metal introduction support

As previously mentioned, zero-valent noble metals such as PO, Pdo, RKC, etc., are typically used on catalytic oxidation catalysts for VOCs. The synthesis method directly affects the distribution, fallout, and form of metal species on supports. Table 4 summarizes the differences in the form and distribution of noble metals introduced by different synthesis strategies, including conventional synthesis and in situ synthesis.

Conventional synthesis methods usually include ion exchange, impregnation, and some specialized monatomic synthesis methods [88,91,148,166,167]. The ion-exchange method can successfully introduce isolated metal cations into the zeolite micropores and attach them to the backbone O atoms by electrostatic interaction, but there is a limitation of low metal uploading [168,169]. The impregnation method, as the most widely used metal introduction strategy, can restrict metal to the outer surface of the zeolite and within the micropores in various forms such as isolated cations, clusters, or nanoparticles with a very high metal uploading rate [170- 172]. However, the position of metal loading is not controllable, and it is easy to form large particles on the outer surface of zeolite supports [88,91]. Noting that the metal introduced by the above two methods mostly exists in the ionic or oxidized state in zeolites, to highly active and highly dispersed zero-valent Pt species for VOCs catalytic combustion, certain post-treatment means are commonly needed. The H, reduction has been most widely used for obtaining Pt" species supported on zeolites [88,91,173]. As summarized in Table 4, the noble metals introduced by the impregnation method followed by H, reduction usually form larger-sized metal nanoparticles on the surface of zeolites [97], whereas the noble metals introduced by the ion-exchange method are mostly in the form of slightly smaller clusters [88,157]. It should be mentioned that the temperature for H, reduction treatment plays a crucial role in determining the formation of active species. As was found by Jiang et al. [174], higher reduction temperatures are more effective in promoting precursor reduction, resulting in a greater proportion of Р© (РИНВ - 350 °C (31.4%) < PVHB - 450 °С (59.0%) < РИНВ - 600 °C (60.9%)). However, excessively high temperatures also can cause Pt particles to aggregate and deactivate, ultimately affecting catalytic activity.

Compared with H, reduction post-treatment, chemical reduction methods using a reducing agent during the catalyst preparation process are also preferred due to their low energy consumption and risk [175-177]. The commonly used strong reducing agents are NaBH, and N,H,, both of which can efficiently reduce noble metals in ionic or oxidized states to metal nanoparticles, but the difference in reduction potentials in solution (1.24 У (NaBH,) and 1.15 У (N,H,)) can affect the morphology and particle size of the formed metal nanoparticles [178]. As shown in Fig. 13 a-b reported by Ntombizodwa et al. [179], Pt-Co nanoparticles prepared by N,H, had smaller and more dispersed particle sizes. Since strong reductants require the addition of certain protective agents to prevent the rapidly forming smaller metal nanoparticles from migrating and agglomerating, some weak reductants that do not require protective agents are widely used. For example, Pt/ zeolite catalysts with controllable particle sizes could be synthesized in one step by adding zeolite to the ethylene glycol solution (weak reductant) containing Pt precursors without post-treatment [144,180]. So the destruction of zeolite support during H, heat treatment could be effectively avoided [158]. Reduction time is a crucial element in the preparation of zeolite supported single metal sites through chemical reduction techniques. An's group [160] employed methanol as the reducing agent to produce Pd/SBA-15. They discovered that the loaded reactive Pt species changed from isolated monoatomic states to particles of 4-17 nm when the reduction time was increased from 30 min to 60 min, as shown in Fig. 13 c-e.

Many methods have been proposed to achieve high dispersion metal loading, including surface modification, precipitation deposition, electrostatic adsorption and thermal dispersion of nanoparticles. In Kumar et al.'s experiments [181], Au/SBA-15 prepared by the homogeneous depositationprecipitation method had higher noble metal loading capacity and better dispersion than the catalyst prepared by the impregnation method, and showed excellent catalytic activity and selectivity of benzyl alcohol at 320 °C. Similarly, Jiang et al. used supercritical fluid deposition to prepare Pt/Beta catalyst, and obtained Pt nanoparticles with more uniform dispersion and smaller particle size (~1.6 nm) [182], showing excellent catalytic activity of toluene, Too% only 178 °C. Recently, atomic layer deposition (ALD) technique has also been used to prepare metal zeolite catalysts, which can be controlled and oriented to load metal atoms onto zeolite support [183,184]. For example, highly dispersed Pt clusters with a uniform size of 0.8 nm were successfully introduced into the micropores of KL (LTL-type) zeolites using the ALD method [159]. However, the synthesis equipment of this method is complex, and the possibility of popularization is small. The synthesis step of surface ligand modification method is relatively simple. The atom dispersion loading of noble metal can be induced by the surface modification of the support with organic ligands. As shown in Fig. 14, using 3-mercaptopropyltrimethoxysilane as surface modifier to support, the Торо of Pt/ZSM-5 catalyst obtained is 164 °C, which shows excellent long-term stability and water resistance, can still achieve complete conversion after 12 h of water vapor introduction [185].

Recently, in-situ synthesis method of encapsulating metals inside zeolites has been widely reported by introducing metal sources during the crystallization process of zeolite. The stable skeleton structure of zeolites can promote the dispersion of noble metals and inhibit the agglomeration of metal nanoparticles, and the size of metal particles and uniformity can be well controlled by spatial confinement of zeolite channels [186]. Based on the precursor ligand type, in situ synthesis can be categorized into stabilization through organic ligands, stabilization using solid precursors, and inter-zeolite transformation methods [187,188]. The organic ligand stabilization method can promote the dispersion of ultrafine noble metal clusters in the micropores of zeolite [189-192]. For instance, Peng et al. [67] used [Ru(NH,CH,CH,NH,)3]Cl; as the precursor to synthesize ultrafine Ru nanoclusters (Ru@S-1) encapsulated in S-1 zeolite, with sizes as low as 0.95 nm, in the propane catalytic process, shows great thermal stability and water resistance. Liu et al. [131] co-introduced ethylenediamine and Pt cation coordination into the synthesis gel of Y-type zeolite. Since the ß-cage of Y-type zeolite can accommodate only one ethylenediamine-Pt complex, the Ptcomplex is isolated and dispersed in the micropores of zeolite. Upon thermal treatment with flowing air and reduction with H, (Fig. 15a), the organic ligands are removed and dispersed Pt single atoms could be formed in the B-cage of Y zeolite. Furthermore, the methods will also affect the catalytic reaction path. Zhang et al. [193]used in-situ synthesis and impregnation methods to prepare Pt-Pd@HMS and Pt-Pd-HMS catalysts for toluene oxidation, found that toluene simultaneously generated benzoic acid and aliphatic carbonyl on PtPd@HMS, accelerating toluene Oxidation. On the contrary, on Pt-Pd-HMS, the intermediate product is benzoic acid, which needs to be further regenerated into aliphatic compounds and finally oxidized to CO, and H,O, so the toluene oxidation rate is lower. Alongside organic molecular ligands, certain solid supports can also be utilized as solid ligands to stabilize metal species, serving as starting materials or crystallization seeds for subsequent in situ fabrication of zeolite-confined metal catalysts [165,194]. Zhang et al. [164] impregnated beta zeolite with H,PtClg aqueous solution, then prepared Pd/Beta by H, reduction and added it as zeolite seed into aluminosilicate gel for hydrothermal crystallization to obtain Pt@Beta catalyst, in which Pt was encapsulated within zeolite crystals as clusters of 0.8-3.2 nm. Compared to the Pt/beta catalyst prepared by the impregnation method, the Pt@Beta catalyst greatly improves CO oxidation, and the T100% is reduced by 65 °C. Furthermore, to simplify the synthesis steps, some researchers have proposed the use of amorphous silica as a solid ligand [195,196]. Fig. 15b, displays the encapsulation of the Pd nanoparticle using amorphous SiO, derived from the controlled hydrolysis of tetraethyl orthosilicate in a Pd nanoparticle solution stabilized by polyvinylpyrrolidone. The addition of tetrapropyl ammonium hydroxide solution followed this step. Solvent-free crystallization at high temperature and pressure yielded Pt@S-1, Pt in the form of nanoparticles with larger particle sizes anchored within the crystals of S-1 zeolite [165]. Due to the harsh synthesis conditions of some small and medium pore zeolites, it is difficult to form more dispersed noble metal@zeolite catalysts by direct in-situ synthesis, so the interzeolite transformation strategy has been proposed [197,198]. For instance, Goel [199] uses Rh@BFA or Rh@FAU as the parent zeolite for recrystallization and successfully converts it into metal @MFI zeolite, effectively encapsulating metal clusters inside MFI zeolite. Similarly, Corma's [163] team confined single Pt atoms and Pt clusters to the extremely stable pure silicon MCM-22 zeolite by converting two-dimensional layered precursors into three-dimensional zeolites. Sun et al. [200] constructed a Pd-containing zeolite seed crystal, and then directionally synthesized Pd;@Beta in a two-step process through hydrothermal treatment of gel and secondary crystallization. The Pd clusters confined in the pores of beta zeolite showed better dispersion, the interaction with the molecular sieve carrier is significantly enhanced, and the final Tso% and Togo of toluene conversion are 169 °C and 187 °C respectively.

3.3. Comparison of active site construction strategies

Section 3 summarizes strategies for constructing active noble metal sites on zeolite-based PNA and VOC catalysts. It focuses on metal precursors, support structures, and noble metal introduction. Here's a summary of similarities and differences in active site construction between PNA and VOC catalysts. Firstly, in terms of precursor selection, both materials tend to use precursors that can generate cationic complexes; for PNA, precursors containing NH; groups can bring more dispersed Pd", whereas for VOCs, H,PtClg, which generates highly dispersed spatial octahedral Pt(IV) clusters, can bring better catalytic activity instead. Secondly, in terms of requirements for supports, although small-pore zeolites like SSZ-13 and SSZ-39 pose certain mass transfer problems caused by large precursor accessing the narrow pore size, the strong carrier Brgnsted acid, excellent hydrothermal stability, low mobility, and NO, storage stability over a relatively wide temperature range (80-180 °C) make these small-size zeolites highly potential for practical applications as PNA compared to large- and medium-pore zeolites. Furthermore, the anchoring of isolated palladium ions in zeolites is determined by the charge-compensated Al centers. Therefore, zeolites with higher Al content (i.e., lower Si/Al) have a higher capacity to accommodate Pd?·. As for VOC catalysts, medium- and macroporous or mesoporous zeolites are often used as supports. Zeolites with larger pore sizes can effectively reduce the spatial site resistance, increase the diffusion rate of VOCs, and improve the catalytic activity. The VOC catalysts also differ in the requirement of carrier Si/Al. Although stronger acidity can accelerate the adsorption activation of VOCs, the carbon accumulation brought by the carrier acidity makes the catalysts extremely easy to deactivate, so higher Si/Al ratio zeolite is more favored in VOC catalysis, which gives the catalysts excellent hydrophobicity and stability. Finally, in terms of metal introductions, the preparation methods for PNA and VOC catalysts differ due to their distinct requirements for the active species. For PNA, since the active species is ionic Pd, loading by ion exchange or impregnation is preferred and hydrothermal aging of the catalyst is usually required to rediapers the Pd··. For VOC catalysts, since the active species are mostly zero-valent metals, the key to the preparation method is how to make the noble metals distributed in isolation to avoid metal agglomeration into clusters during the subsequent reduction activation process. Therefore, in addition to the commonly used impregnation method, VOC catalysts are prepared by the in-situ synthesis method to encapsulate the noble metals in zeolites in isolation.

4. Zeolite-based monolithic catalyst

Recently, reports on monolithic catalysts have gradually increased. Compared with particle catalysts, they have better mass transfer, heat transfer performance and thermal stability. Monolithic catalysts have many parallel channels or macroscopic pore structures, which usually exhibit Low pressure drop and excellent clogging resistance.

In the field of catalytic oxidation of VOCs, the washcoating is the most common approach to load active phase catalysts onto supports. For example, cordierite is a frequently used support for monolithic catalysts and has been widely studied due to its high density, low bulk density, and low coefficient of thermal expansion. Ribeiro's [201] application of Pt/ZSM-5 onto cordierite supports, the open structure of the foamed cordierite, the homogeneous and well adhered deposition of zeolite and the loaded noble metal Pt resulted in excellent toluene degradation activity (Tso = 210 °C, 800 ppm toluene in 15 Lh' air flow). However, the catalysts prepared by this method were poorly shock-resistant, the coatings were prone to peeling off, and the thicker coatings resulted in low heat transfer and conductivity, as well as lower active phase utilization. Therefore, researchers have developed new preparation methods, including in situ growth, 3D printing, and so on. In situ generation of zeolites directly on the support and then loading with noble metals can minimize the catalyst layer thickness and inhibit exfoliation. For instance, Marin et al. [202] used microwave-assisted seeded hydrothermal synthesis to generate a homogeneous ZSM-5 zeolite layer of about 680 nm in situ on the outer surface of silicon carbide, and the resulting ZSM-5 coated monolith, after loading with Pt by ion exchange, showed excellent activity in the catalytic oxidation of trace amounts of n-hexane, and achieved a complete conversion at 268 °C. Recently, the application of 3D printing technology to the preparation of monolithic catalysts has attracted attention, and the method that can directly batch print the monolithic architecture after finalizing the structure has a greater potential for industrial application than the traditional complex preparation steps. Yang et al. [203] used 3D printing technology to produce structured ZSM-5 zeolites and loaded them with 0.42 wt% of Pt by impregnation, and the resultant catalysts had extremely high compressive strength, and also effectively improved the conversion and selectivity of ethylbenzene.

As one of the links of the actual vehicle exhaust treatment system, the research and development of monolithic PNA catalyst is necessary, but there are few studies on the design of monolithic PNA catalysts, and most of them focus on the stability and anti-toxicity of monolithic PNA catalysts prepared by the traditional washing coating method. Theis first evaluated a monolithic catalyst containing 0.92 g L7! Pt or Pd on an alumina support and investigated the contribution of the noble metal and wash coating to МО, storage performance [44]. Then, Theis used three zeolites (BEA, CHA and MFI) containing Pd as washing coatings to prepare monolithic NO, adsorbent. Among them, CHA provides the best NO, storage and release performance, BEA shows the strongest thermal stability, and the NO, storage performance of all three samples decreases when the feedstock gas contains CO [204]. In addition, the choice of support is crucial for Pd-based monolithic catalysts. For example, in Wang's experiment [100], Pd/ LTA and Pd/SSZ-13 monomer catalysts were prepared by the washing coating method, as shown in Fig. 16. Compared with the latter, Pd/LTA showed better hydrothermal stability, and the NO, adsorption effect was improved more obviously in the presence of CO.

5. Summary and prospect

Noble metal/zeolite materials have developed rapidly in various important adsorption and catalysis processes. And the high cost and catalyst stability issues of noble metals make it urgent to develop construction strategies that can achieve high stability and high dispersion load of noble metals. In this paper, we first present the current status of the application of noble metal/zeolite materials in the purification of two typical air pollutants, NO, and VOCs, and compare the active substances used in both, where Pd?· and PS are the main active centers for PNA and VOC catalyst. Secondly, the current construction strategies used for the active species in different scenarios are summarized in terms of preparation methods, catalyst composition, etc., where ion exchange and impregnation are the main synthetic methods used for metal cation encapsulation, while in situ synthesis, ALD and inter zeolite conversion for single-atom metal or oxide cluster encapsulation are also considered. The morphology of noble metal precursors, topology of zeolite support, pore size, skeletal Si/ Al, and heteroatom doping all influence the morphology, distribution position, and dispersion of noble metal-loaded supports. Finally, we also briefly introduce the progress of monolithic catalysts used in PNA and VOCs catalysts. On this basis, we hope to provide some references for the targeted loading of different active species on zeolites.

Although some progress has been made in the noble metal construction strategies for zeolite-loaded catalysts, there are still many outstanding issues to be solved: (1) The synthesis of adsorption/catalysts with excellent activity by adjusting the zeolite structure. (2) Selecting more stable metal precursors and zeolites with excellent binding structures to enhance the interaction between metal precursors and zeolite carriers and ensure that metal precursors are introduced into zeolite pores in ideal forms and converted into target metal species under various treatments such as subsequent reduction or hydrothermal aging. (3) Explore the realization of NO, low-temperature adsorption and VOCs catalysis on the same noble metal/zeolite material, which is important for the synergistic removal of multi-pollutant exhaust of dilute combustion engines. (4) To study other green and sustainable pathways for zeolite encapsulation of noble metals, such as an integrated pathway combining multiple encapsulation strategies.

CRediT authorship contribution statement

Yuan Yao: Writing - original draft, Visualization, Investigation. Haodan Cheng: Visualization, Investigation. Guocai Zhong: Validation, Project administration. Xiaolong Tang: Supervision, Funding acquisition. Honghong Yi: Supervision, Resources. Shunzheng Zhao: Writing - review & editing. Fengyu Gao: Writing - review & editing. Qingjun Yu: Writing - review ¿ editing, Methodology, Conceptualization.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was supported by Zhongtian Iron and Steel - University of Science and Technology Beijing Youth Science and Technology Innovation Fund (No. FZTNTC2024050005) National Engineering Laboratory for Mobile Source Emission Control Technology, China (No. NELMS2020A07); The Fundamental Research Funds for the Central Universities, China (No. FRF-AT-20-12).

Sidebar

Yuan Yao: A graduate student of University of Science and Technology Beijing in China. Her current research interest lies in Technology of Air Pollution Control.

Haodan Cheng: A graduate student of University of Science and Technology Beijing in China. Her current research interest lies in Technology of Air Pollution Control.

Guocai Zhong: Petr°China Sichuan Petrochemical Co., Ltd.

Xiaolong Tang: A professor in Department of Environmental Engineering at University of Science and Technology Beijing in China. His current research interest lies in Theory and Technology of Air Pollution Control, Environment Function Materials.

Honghong Yi: A professor in Department of Environmental Engineering at University of Science and Technology Beijing in China. Her current research interest lies in Theory and Technology of Air Pollution Control, Environment Function Materials.

Shunzheng Zhao: An associate professor in Department of Environmental Engineering at University of Science and Technology Beijing in China. His current research interest lies in Environmental Functional Materials, Air Pollution Control Engineering.

Fengyu Gao: An associate professor in Department of Environmental Engineering at University of Science and Technology Beijing in China. His current research interest lies in Theory and Technology of Air Pollution Control, Environment Catalytic Materials.

Qingjun Yu: An associate professor in Department of Environmental Engineering at University of Science and Technology Beijing in China. Her current research interest lies in Theory and Technology of Air Pollution Control, Zeolitic Adsorption & Catalytic Materials.

References

References

[1] K. Qiu, L. Yang, J. Lin, P. Wang, Y. Yang, D. Ye, L. Wang, Atmos. Environ. 86 (2014) 102-112.

[2] General Office of the State Council. http://www.gov.cn/zhengce/202111/07/content_5649656.htm.

[3] Ministry of Ecology and Environment of the People's Republic of China. https://www.mee.gov.cn/hjzl/sthjzk/sthjtjnb/202301/t20230118_ 1013682.shtml.

[4] Y.X. Sun, E. Zwolinska, A.G. Chmielewski, Crit. Rev. Environ. Sci. Technol. 46 (2016) 119-142.

[5] M. Moliner, A. Corma, React. Chem. Eng. 4 (2019) 223-234.

[6] R.T. Guo, J.K. Hao, W.G. Pan, Y.L. Yu, Separ. Sci. Technol. 50 (2015) 310-321.

[7] Е. Heymes, P. Manno-Demoustier, Е. Charbit, J.L. Fanlo, P. Moulin, Chem. Eng. J. 115 (2006) 225-231.

[8] M.S. Kamal, S.A. Razzak, M.M. Hossain, Atmos. Environ. 140 (2016) 117-134.

[9] P. Dwivedi, V. Gaur, A. Sharma, N. Verma, Separ. Sci. Technol. 39 (2004) 23-37.

[10] S. Song, S. Zhang, X. Zhang, P. Verma, M. Wen, Front. Mater. 7 (2020) 595667.

[11] J. Kujawa, $. Cerneaux, W. Kujawski, J. Membr. Sci. 474 (2015) 11- 19.

[12] Y.L. Guo, M.C. Wen, G.Y. Li, T.C. An, Appl. Catal. B Environ. 281 (2021) 119447.

[13] С. Bian, D. Li, О. Liu, S.T. Zhang, L. Pang, Z. Luo, Y.B. Guo, Z. Chen, T. Li, Chin. Chem. Lett. 33 (2022) 1169-1179.

[14] H.Y. Chen, J.E. Collier, D.X. Liu, L. Mantarosie, D. Duran-Martin, У. Novak, К.К. Rajaram, D. Thompsett, Catal. Lett. 146 (2016) 1706- 1711.

[15] C. Descorme, P. Gélin, M. Primet, C. Lécuyer, Catal. Lett. 41 (1996) 133-138.

[16] C. He, J. Cheng, X. Zhang, M. Douthwaite, S. Pattisson, Z. Hao, Chem. Rev. 119 (2019) 4471-4568.

[17] H.-S. Kim, H.-J. Kim, J.-H. Kim, J.-H. Kim, S.-H. Kang, J.-H. Ryu, N.K. Park, D.-S. Yun, J.-W. Bae, Catalysts 12 (2022) 63-81.

[18] L.F. Liotta, Appl. Catal. В Environ. 100 (2010) 403-412.

[19] G.I. Golodets, Heterogeneous Catalytic Reactions Involving Molecular Oxygen, OSTI, United States, 1983.

[20] H. Huang, Y. Xu, Q. Feng, D.Y.C. Leung, Catal. Sci. Technol. 5 (2015) 2649-2669.

[21] A. Corma, Chem. Rev. 97 (1997) 2373-2420.

[22] Y. Li, L. Li, J. Yu, Chem 3 (2017) 928-949.

[23] L. Zhang, H. Duan, Z. Tan, Q. Wu, X. Meng, F. Xiao, Chem. J. Chin. Univ. 41 (2020) 19-27.

[24] H. Feng, С. Li, H.S. Shan, Appl. Clay Sci. 42 (2009) 439-445.

[25] A. Aranzabal, М. Romero-Sáez, U. Elizundia, J.R. González-Velasco, J.A. González-Marcos, J. Catal. 296 (2012) 165-174.

[26] M. Paulis, H. Peyrard, M. Montes, J. Catal. 199 (2001) 30-40.

[27] N.W. Cant, Р.Е. Angove, M.J. Patterson, Catal. Today 44 (1998) 93-99.

[28] N. Radic, B. Grbic, A. Terlecki-Baricevic, Appl. Catal. B Environ. 50 (2004) 153-159.

[29] S. Benard, M. Ousmane, L. Retailleau, A. Boreave, P. Vernoux, A. Giroir-Fendler, Can. J. Civ. Eng. 36 (2009) 1935-1945.

[30] Y. Ji, S. Bai, M. Crocker, Appl. Catal. В Environ. 170 (2015) 283- 292.

[31] S.X. Ren, S.J. Schmieg, C.K. Koch, G.S. Qi, W. Li, Catal. Today 258 (2015) 378-385.

[32] P. Khatri, D. Bhatia, Catal. Lett. 151 (2021) 3298-3312.

[33] E.A. Kyriakidou, J. Lee, J.S. Choi, M. Lance, T.J. Toops, Catal. Today 360 (2021) 220-233.

[34] К. Khivantsev, N.R. Jaegers, Н.А. Aleksandrov, I. Song, X.I. PereiraHernandez, М.Н. Engelhard, J. Tian, L. Chen, D.M. Meira, L. Kovarik, G.N. Vayssilov, Y. Wang, J. Szanyi, J. Am. Chem. Soc. 145 (2023) 5029-5040.

[35] Y. Ryou, J. Lee, S.J. Cho, H. Lee, С.Н. Kim, D.H. Kim, Appl. Catal. В Environ. 212 (2017) 140-149.

[36] Y. Ryou, J. Lee, Y. Kim, $. Hwang, H. Lee, С.Н. Kim, D.H. Kim, Appl. Catal. A-Gen. 569 (2019) 28-34.

[37] Y. Zheng, L. Kovarik, М.Н. Engelhard, Y.L. Wang, У. Wang, Е. Gao, J. Szanyi, J. Phys. Chem. С 121 (2017) 15793-15803.

[38] J. Lee, Y. Ryou, S.J. Cho, H. Lee, C.H. Kim, D.H. Kim, Appl. Catal. B Environ. 226 (2018) 71-82.

[39] V. Anh, J. Luo, J. Li, W.S. Epling, Catal. Lett. 147 (2017) 745-750.

[40] Y.L. Shan, Y. Sun, Y.B. Li, X.Y. Shi, W.P. Shan, Y.B. Yu, H. He, Top. Catal. 63 (2020) 944-953.

[41] M. Jarvis, K.M. Adams, Method for Converting Exhaust Gases from a Diesel Engine Using Nitrogen Oxide Absorbent, United States Patents: US6182443B1.

[42] V. Mesilov, L. Pon, S. Dahlin, S.L. Bergman, L.J. Pettersson, S.L. Bernasek, J. Phys. Chem. С 126 (2022) 7022-7035.

[43] Р.Н. Ho, J. Woo, К.Е. Ilmasani, M.A. Salam, D. Creaser, L. Olsson, ACS Eng. Au. 2 (2021) 27-45.

[44] J.R. Theis, Catal. Today 267 (2016) 93-109.

[45] $. Tamm, $. Andonova, L. Olsson, Catal. Lett. 144 (2014) 674-684.

[46] S. Tamm, S. Andonova, L. Olsson, Catal. Lett. 144 (2014) 1101-1112.

[47] P. Khatri, D. Bhatia, Appl. Catal. A-Gen. 618 (2021) 118114.

[48] M.V. Twigg, Rev. 55 (2011) 43-53.

[49] S. Jones, Y. Ji, M. Crocker, Catal. Lett. 146 (2016) 909-917.

[50] Y. Ryou, J. Lee, H. Lee, С.Н. Kim, D.H. Kim, Catal. Today 307 (2018) 93-101.

[51] T.J. Toops, A.J. Binder, P. Kunal, E.A. Kyriakidou, J.S. Choi, Catalysts 11 (2021) 449.

[52] Y. Ryou, J. Lee, H. Lee, C.H. Kim, D.H. Kim, Catal. Today 297 (2017) 53-59.

[53] J. Lee, J.R. Theis, E.A. Kyriakidou, Appl. Catal. B Environ. 243 (2019) 397-414.

[54] Y.T. Gu, W.S. Epling, Appl. Catal. A-Gen. 570 (2019) 1-14.

[55] Y. Wang, X. Yong, M. Rong, J. Zheng, H. Zhao, J. Chin, Chem. SocTaip 67 (2020) 1530-1543.

[56] М. Ambast, К. Karinshak, B.M.M. Rahman, L.C. Grabow, М.Р. Harold, Appl. Catal. B Environ. 269 (2020) 118802.

[57] D.H. Mei, Е. Gao, J. Szanyi, У. Wang, Appl. Catal. A-Gen. 569 (2019) 181-189.

[58] K. Mandal, Y. Gu, K.S. Westendorff, S. Li, J.A. Pihl, L.C. Grabow, W.S. Epling, C. Paolucci, ACS Catal. 10 (2020) 12801-12818.

[59] J. Lee, Y. Kim, S. Hwang, E. Lee, H. Lee, C.H. Kim, D.H. Kim, Catal. Today 360 (2021) 350-355.

[60] К.Е. Ilmasani, J. Woo, D. Creaser, L. Olsson, Ind. Eng. Chem. Res. 59 (2020) 9830-9840.

[61] Е. Villamaina, U. Iacobone, I. Nova, E. Tronconi, М.Р. Ruggeri, L. Mantarosie, J. Collier, D. Thompsett, Appl. Catal. B Environ. 284 (2021) 119724.

[62] M. Jiang, J. Wang, J. Wang, M. Shen, Materials 12 (2019) 1045.

[63] Z. Zhang, Z. Jiang, W. Shangguan, Catal. Today 264 (2016) 270-278.

[64] C. Yang, G. Miao, Y. Pi, Q. Xia, J. Wu, Z. Li, J. Xiao, Chem. Eng. J. 370 (2019) 1128-1153.

[65] H.L. Yang, C.Y. Ma, Y. Li, J.H. Wang, X. Zhang, С. Wang, N.L. Qiao, Y.G. Sun, J. Cheng, Z.P. Hao, Chem. Eng. J. 347 (2018) 808-818.

[66] S.Y. Tang, H.Y. Liu, T.S. Li, С. Wang, Q.Y. Cui, Y.Y. Yue, X.H. Meng, X.J. Bao, Chem. Eng. Sci. 286 (2024) 119674.

[67] J.X. Tao, QL. Zhang, Y.H. Zhao, Н.А. Chen, W.M. Liu, Y.Z. He, Y.N. Yin, TY. He, J. Chen, X.F. Wang, D.S. Wu, Н.С. Peng, Chemosphere 302 (2022) 134884.

[68] S. Scire, S. Minico, C. Crisafulli, C. Satriano, A. Pistone, Appl. Catal. B Environ. 40 (2003) 43-49.

[69] B. Zhao, B. Jin, X. Wu, D. Weng, R. Ran, Catal. Commun. 167 (2022) 106456.

[70] Y.H. Chin, C. Buda, M. Neurock, E. Iglesia, J. Am. Chem. Soc. 135 (2013) 15425-15442.

[71] S.Y. Chen, S.D. Li, R.Y. You, Z.Y. Guo, Е. Wang, G.X. Li, W.T. Yuan, B.E. Zhu, Y. Gao, Z. Zhang, H.S. Yang, Y. Wang, ACS Catal. 11 (2021) 5666-5677.

[72] C. He, J. Li, P. Li, J. Cheng, Z. Hao, Z.-P. Xu, Appl. Catal. B Environ. 96 (2010) 466-475.

[73] Y. Lou, J. Ma, W.D. Hu, Q.G. Dai, L. Wang, W.C. Zhan, Y.L. Guo, X.M. Cao, Y. Guo, P. Hu, G.Z. Lu, ACS Catal. 6 (2016) 8127-8139.

[74] M. Jablonska, A. Krol, E. Kukulska-Zajac, K. Tarach, V. Girman, L. Chmielarz, К. Gora-Marek, Appl. Catal. В Environ. 166 (2015) 353- 365.

[75] J.M. Giraudon, A. Elhachimi, G. Leclercq, Appl. Catal. B Environ. 84 (2008) 251-261.

[76] $. Ordonez, L. Bello, H. Sastre, В. Rosal, Е.М. Diez, Appl. Catal. В Environ. 38 (2002) 139-149.

[77] Е. Beauchet, P. Magnoux, J. Mijoin, Catal. Today 124 (2007) 118-123.

[78] H. Luo, X.-D. Wu, D. Weng, S. Liu, R. Ran, Rare Met. 36 (2017) 1-9.

[79] Z. Zhu, G. Lu, Y. Guo, Y. Guo, Z. Zhang, Y. Wang, X.Q. Gong, ChemCatChem 5 (2013) 2495-2503.

[80] C. Chen, F. Chen, L. Zhang, S. Pan, C. Bian, X. Zheng, X. Meng, F.$. Xiao, Chem. Commun. 51 (2015) 5936-5938.

[81] L. Pinard, J. Mijoin, P. Magnoux, M. Guisnet, С.Е. Chim. 8 (2005) 457- 463.

[82] Y. Wang, Y. Chen, L. Zhang, С. Wang, W. Deng, Г.М. Guo, Microporous Mesoporous Mater. 308 (2020) 110538.

[83] Y. Su, К. Fu, Y. Zheng, N. Ji, С. Song, D. Ma, X. Lu, К. Han, О. Liu, Appl. Catal. B Environ. 288 (2021) 119980.

[84] J.E. Park, К.В. Kim, Y.-A. Kim, K.S. Song, Е.Р. Park, Catal. Lett. 143 (2013) 1132-1138.

[85] AM. Ali, M.A. Daous, A. Arafat, A.A. Alzahrani, Y. Alhamed, A. Tuerdimaimaiti, L.A. Petrov, J. Nanomater. 2015 (2015) 901439.

[86] H. Yang, C. Ma, G. Wang, Y. Sun, J. Cheng, Z. Zhang, X. Zhang, Z. Hao, Catal. Sci. Technol. 8 (2018) 1988-1996.

[87] H. Yang, C. Ma, X. Zhang, Y. Li, J. Cheng, Z. Hao, ACS Catal. 8 (2018) 1248-1258.

[88] Y. Jiang, L. Zhang, Y. Xie, S. Han, О. Zhu, X. Meng, F.-S. Xiao, Catal. Today 355 (2020) 476-481.

[89] B. Wu, B. Chen, X. Zhu, L. Yu, C. Shi, Catal. Today 355 (2020) 512-517.

[90] С. He, P. Li, J. Cheng, Z.-P. Hao, Z.-P. Xu, Soil. Poll. 209 (2010) 365- 376.

[91] С. Chen, X. Wang, J. Zhang, $. Pan, С. Bian, L. Wang, Е. Chen, X. Meng, X. Zheng, X. Gao, Catal. Lett. 144 (2014) 1851-1859.

[92] C. He, J. Li, X. Zhang, L. Yin, J. Chen, S. Gao, Chem. Eng. J. 180 (2012) 46-56.

[93] H. Chen, Z. Rui, X. Wang, H. Ji, Catal. Today 258 (2015) 56-63.

[94] L. Zhang, Y. Jiang, B.-B. Chen, C. Shi, Y. Li, C. Wang, S. Han, S. Pan, L. Wang, X. Meng, Catal. Today 339 (2020) 174-180.

[95] L. Zhang, Y. Xie, Y. Jiang, Y. Li, C. Wang, S. Han, H. Luan, X. Meng, F.-S. Xiao, Appl. Catal. В Environ. 268 (2020) 118461.

[96] S. Scirè, $. Minico, С. Crisafulli, Appl. Catal. В Environ. 45 (2003) 117-125.

[97] Y. Kim, J. Sung, S. Kang, J. Lee, M.-H. Kang, S. Hwang, H. Park, J. Kim, Y. Kim, E. Lee, J. Mater. Chem. A 9 (2021) 19796-19806.

[98] K. Khivantsev, N.R. Jaegers, L. Kovarik, J.C. Hanson, F. Tao, Y. Tang, X. Zhang, 1.7. Koleva, Н.А. Aleksandrov, С.М. Vayssilov, Angew. Chem., Int. Ed. 57 (2018) 16672-16677.

[99] J. Lee, Y. Ryou, S. Hwang, Y. Kim, S.J. Cho, H. Lee, C.H. Kim, D.H. Kim, Catal. Sci. Technol. 9 (2019) 163-173.

[100] Y. Wang, X. Shi, Z. Liu, Y. Shan, W. Shi, Y. Yu, H. He, Appl. Catal. B Environ. 324 (2023) 122254.

[101] K. Khivantsev, N.R. Jaegers, L. Kovarik, J.Z. Hu, F. Gao, Y. Wang, J. Szanyi, Emission Control Sci. Tech. 6 (2020) 126-138.

[102] K. Khivantsev, N.R. Jaegers, L. Kovarik, M. Wang, J.Z. Hu, Y. Wang, M.A. Derewinski, J. Szanyi, Appl. Catal. B Environ. 280 (2021) 119449.

[103] L. Castoldi, R. Matarrese, S. Morandi, P. Ticali, L. Lietti, Catal. Today 360 (2021) 317-325.

[104] K. Khivantsev, X. Wei, L. Kovarik, N.R. Jaegers, E.D. Walter, P. Tran, Y. Wang, J. Szanyi, Angew. Chem.-Int. Edit. 61 (2022) e202107554.

[105] H. Zhao, X. Chen, A. Bhat, Y. Li, J.W. Schwank, Appl. Catal. В Environ. 282 (2021) 119611.

[106] S. Han, J. Cheng, C. Zheng, Q. Ye, S. Cheng, T. Kang, H. Dai, Appl. Surf. Sci. 419 (2017) 382-392.

[107] J. Lee, J. Kim, Y. Kim, S. Hwang, H. Lee, C.H. Kim, D.H. Kim, Appl. Catal. B Environ. 277 (2020) 119190.

[108] К. Khivantsev, Е. Gao, L. Kovarik, Y. Wang, J. Szanyi, J. Phys. Chem. С 122 (2018) 10820-10827.

[109] J.R. Theis, J. Ura, A.B. Getsoian, V.Y. Prikhodko, C.R. Thomas, J.A. Pihl, Т.М. Lardinois, К. Gounder, X. Wei, Y. Ji, Appl. Catal. В Environ. 322 (2023) 122074.

[110] К. Khivantsev, NR. Jaegers, L. Kovarik, $. Prodinger, M.A. Derewinski, Y. Wang, F. Gao, J. Szanyi, Appl. Catal. A-Gen. 569 (2019) 141-148.

[111] S. Huang, Q. Wang, Y. Shan, X. Shi, Z. Liu, H. He, Molecules 28 (2023) 3501.

[112] J. Li, K. Fan, Y.L. Shan, S. Wang, J. Zhang, W.B. Fan, H. He, X.Y. Zhao, X.J. Meng, F.S. Xiao, Appl. Catal. В Environ. 339 (2023) 123127.

[113] Y. Zhu, J. Wang, Y. Zhai, G. Shen, J. Wang, C. Wang, M. Shen, Catal. Sci. Technol. 12 (2022) 3464-3473.

[114] Y. Zhu, J. Wang, C. Wang, J. Wang, G. Shen, M. Shen, Catal. Sci. Technol. 13 (2023) 3403-3415.

[115] C. Fan, J. Mi, Q. Wu, J. Chen, J. Li, Processes 10 (2022) 222.

[116] J. Cai, H. Zhao, X. Li, С. Jing, J.W. Schwank, React. Chem. Eng. 8 (2023) 1312-1323.

[117] J. Lee, J. Chen, K. Giewont, T. Mon, C.-H. Liu, E.A. Walker, E.A. Kyriakidou, Chem. Eng. J. 440 (2022) 135834.

[118] 7. Zhao, В. Yu, К. Zhao, С. Shi, Н. Gies, F.-S. Xiao, D. de Vos, T. Yokoi, X. Bao, U. Kolb, Appl. Catal. В Environ. 217 (2017) 421- 428.

[119] L. Liu, W. Xiong, M. Fu, J. Wu, Z. Li, D. Ye, P. Chen, Chin. Chem. Lett. (2023) 108870.

[120] S. Yasumura, H. Ide, T. Ueda, Y. Jing, C. Liu, K. Kon, T. Toyao, Z. Maeno, К.-1. Shimizu, JACS Au. 1 (2021) 201-211.

[121] PN.R. Vennestrom, L.F. Lundegaard, С. Tyrsted, D.A. Bokarev, А.Л. Mytareva, С.М. Baeva, A.Y. Stakheev, T.V.W. Janssens, Top. Catal. 62 (2019) 100-107.

[122] L. Quinones, М.М. Martinez-Inesta, J. Mater. Sci. 46 (2011) 72897297.

[123] E. Belopukhov, E. Paukshtis, V. Shkurenok, M. Smolikov, A. Belyi, Procedia Eng. 113 (2015) 19-25.

[124] P. Maki-Arvela, T.A.K. Khel, M. Azkaar, S. Engblom, D.Y. Murzin, Catalysts 8 (2018) 534.

[125] J. Oenema, R.A. Van Alst, M.J. Meijerink, J. Zeéevié, K.P. de Jong, Appl. Catal. A-Gen. 605 (2020) 117815.

[126] J. Oenema, J.P. Hofmann, E.J. Hensen, J. Zecevic, K.P. de Jong, ChemCatChem 12 (2020) 615-622.

[127] Y.D. Wang, Z. Tao, Y. Li, J. Catal. 322 (2015) 1-13.

[128] L.M.T. Simplicio, S.T. Brandao, Е.А. Sales, L. Lietti, Е. Bozon-Verduraz, Appl. Catal. B Environ. 63 (2006) 9-14.

[129] X.B. Zhu, X.Y. He, L.H. Guo, Y.W. Shi, N. Zhao, C.Z. Qiao, L. Dai, Y.J. Tian, ACS Appl. Nano Mater. 5 (2022) 3374-3385.

[130] Y.C. Chai, S.H. Liu, 7.7. Zhao, J.L. Gong, W.L. Dai, GJ. Wu, N.J. Guan, L.D. Li, ACS Catal. 8 (2018) 8578-8589.

[131] Y.W. Liu, Z. Li, Q.Y. Yu, У.Е. Chen, Z.W. Chai, С.Е. Zhao, S.J. Liu, W.C. Cheong, Y. Pan, О.Н. Zhang, L. Gu, L.R. Zheng, Y. Wang, Y. Lu, D.S. Wang, C. Chen, Q. Peng, Y.Q. Liu, L.M. Liu, J.S. Chen, Y.D. Li, J. Am. Chem. Soc. 141 (2019) 9305-9311.

[132] Z.Y. Di, R.D. Zhang, X.A. Guo, H.X. Shen, Y.P. Li, J.B. Jia, Y. Wei, Environ. Sci. Technol. 57 (2023) 16641-16652.

[133] N. Brodu, S. Sochard, C. Andriantsiferana, J.S. Pic, M.H. Manero, Environ. Technol. 36 (2015) 1807-1818.

[134] A.F. Cosseron, T.J. Daou, L. Tzanis, H. Nouali, I. Deroche, B. Coasne, У. Tchamber, Microporous Mesoporous Mater. 173 (2013) 147-154.

[135] D. Chen, О. Tang, W. Deng, $. Chaianansutcharit L. Guo, Microporous Mesoporous Mater. 346 (2022) 112275.

[136] W.X. Gu, C.Q. Li, J.H. Qiu, J.F. Yao, J. Hazard. Mater. 408 (2021) 124458.

[137] S. Alejandro, H. Valdes, M.H. Manero, C.A. Zaror, Water Sci. Technol. 66 (2012) 1759-1765.

[138] H. Valdes, V.A. Solar, E.H. Cabrera, A.F. Veloso, C.A. Zaror, Chem. Eng. J. 244 (2014) 117-127.

[139] C. Pang, R. Han, Y. Su, Y. Zheng, M. Peng, Q. Liu, Chem. Eng. J. 454 (2023) 140125.

[140] N Navascues, M. Escuin, Y. Rodas, $. Irusta, К. Mallada, J. Santamaria, Ind. Eng. Chem. Res. 49 (2010) 6941-6947.

[141] S. Liu, C. Luo, X. Deng, Y. Fang, Fuel 328 (2022) 125282.

[142] EZ. Kong, С.Е. Li, J.L. Wang, Y.J. Shi, R.X. Zhou, Appl. Surf. Sci. 606 (2022) 154888.

[143] R. El Khawaja, S. Sonar, T. Barakat, N. Heymans, B.L. Su, A. Lofberg, J.F. Lamonier, J.M. Giraudon, G. de Weireld, C. Poupin, R. Cousin, S. Siffert, Catal. Today 405 (2022) 212-220.

[144] J.L. Wang, X.L. Guo, Y.J. Shi, R.X. Zhou, J. Environ. Sci. 107 (2021) 87-97.

[145] C.Y. Chen, J. Zhu, F. Chen, X.J. Meng, X.M. Zheng, X.H. Gao, ES. Xiao, Appl. Catal. В Environ. 140 (2013) 199-205.

[146] EJ. Liu, S.F. Zuo, С. Wang, J.T. Li, ES. Xiao, C.Z. Qi, Appl. Catal. В Environ. 148 (2014) 106-113.

[147] J.Y. Zhang, C. Rao, H.G. Peng, C. Peng, L. Zhang, X.L. Xu, W.M. Liu, Z. Wang, N. Zhang, X. Wang, Chem. Eng. J. 334 (2018) 10-18.

[148] C. He, J.J. Li, J. Cheng, L.D. Li, P. Li, Z.P. Hao, Z.P. Xu, Ind. Eng. Chem. Res. 48 (2009) 6930-6936.

[149] Y. Hao, S. Chen, H. Wang, R. Chen, P. Sun, T. Chen, ACS Appl. Nano Mater. 3 (2020) 8472-8482.

[150] L. Zhang, L. Chen, Y. Li, Y. Peng, Е. Chen, L. Wang, С. Zhang, X. Meng, Н. He, E-S. Xiao, Appl. Catal. В Environ. 219 (2017) 200-208.

[151] Р.О. Li, L. Wang, Y.O. Lu, H. Deng, Z.L. Zhang, Y.J. Wang, Y. Ma, T.T. Pan, О. Zhao, Y.L. Shan, X.Y. Shi, J.Z. Ma, H. He, Appl. Catal. В Environ. 334 (2023) 122811.

[152] М. Li, В. Huang, X. Dong, J.S. Luo, Y. Wang, H. Wang, D.Y. Miao, У. Pan, Е. Jiao, J.P. Xiao, Z.P. Qu, Nat. Commun. 13 (2022) 2209.

[153] Z. Liao, K. Zha, W. Sun, Z. Huang, H. Xu, W. Shen, Catalysts 10 (2020) 1377.

[154] P. Zhao, X. Li, W. Liao, Y. Wang, J. Chen, J. Lu, M. Luo, Ind. Eng. Chem. Res. 58 (2019) 21945-21952.

[155] J.D. Kistler, N. Chotigkrai, P. Xu, В. Enderle, P. Praserthdam, C.Y. Chen, N.D. Browning, B.C. Gates, Angew. Chem. 53 (2014) 8904-8907.

[156] К. Osuga, $. Yasuda, М. Sawada, К. Manabe, H. Shima, S. Tsutsuminai, A. Fukuoka, H. Kobayashi, A. Muramatsu, T. Yokoi, Ind. Eng. Chem. Res. 60 (2021) 8696-8704.

[157] N. Wang, Q. Sun, T. Zhang, A. Mayoral, L. Li, X. Zhou, J. Xu, P. Zhang, J. Yu, J. Am. Chem. Soc. 143 (2021) 6905-6914.

[158] J.L. Wang, Y.J. Shi, FZ. Kong, R.X. Zhou, J. Environ. Sci. 124 (2023) 505-512.

[159] D. Xu, B. Wu, P. Ren, S. Wang, C. Huo, B. Zhang, W. Guo, L. Huang, X. Wen, Y. Qin, Catal. Sci. Technol. 7 (2017) 1342-1350.

[160] М. Wen, S. Song, W. Zhao, О. Liu, J. Chen, С. Li, T. An, Environ. Sci.: Nano 8 (2021) 3735-3745.

[161] Q. Sun, N. Wang, T. Zhang, R. Bai, A. Mayoral, P. Zhang, Q. Zhang, O. Terasaki, J. Yu, Angew. Chem., Int. Ed. 58 (2019) 18570-18576.

[162] S. Zhang, Y. Li, C. Ding, Y. Niu, Y. Zhang, B. Yang, G. Li, J. Wang, Z. Ma, L.-J. Yu, Small. Struct. 4 (2023) 2200115.

[163] L. Liu, U. Diaz, R. Arenal, G. Agostini, P. Concepcion, A. Corma, Nat. Mater. 16 (2017) 132-138.

[164] J. Zhang, L. Wang, B. Zhang, H. Zhao, U. Kolb, Y. Zhu, L. Liu, Y. Han, G. Wang, C. Wang, D.S. Su, B.C. Gates, F.-S. Xiao, Nat. Catal. 1 (2018) 540-546.

[165] С. Wang, L. Wang, J. Zhang, Н. Wang, J.P. Lewis, F.-S. Xiao, J. Am. Chem. Soc. 138 (2016) 7880-7883.

[166] C. He, Q. Shen, M.X. Liu, J. Porous. Mats. 21 (2014) 551-563.

[167] J.Q. He, D.Y. Chen, N.J. Li, О.Е. Xu, H. Li, J.H. He, J.M. Lu, Appl. Catal. B Environ. 265 (2020) 118560.

[168] Y. Yamasaki, M. Matsuoka, M. Anpo, Catal. Lett. 91 (2003) 111-113.

[169] Y.Y. Shao, С.Р. Yin, J.J. Wang, Y.Z. Gao, Р.Е. Shi, J. Electrochem. Soc. 153 (2006) А1261-А1265.

[170] S.V. De Vyver, E. D'hondt, В.Е. Sels РА, Jacobs In Preparation of Pt on NaY zeolite catalysts for conversion of glycerol into 1,2-propanediol. 10th International Symposium on the Scientific Bases for the Preparation of Heterogeneous Catalysts, Univ Catholique Louvain (UCL), Louvain-la-Neuve, BELGIUM, 2010, pp. 771-774.

[171] Z. Li, W. Yan S. Wei, XAFS study of HY zeolite supported Pt nanoparticle catalysts prepared with different methods, Stanford, CA, in: 13th International Conference on X-Ray Absorption Fine Structure (XAFS13), 2006, 714.

[172] M. Wang, X. Liu, K. Ren, Y. Zhou, T. Li, Y. Bi, H. Kang, E. Xing, Q. Chen, Catal. Lett. 151 (2021) 2684-2695.

[173] C.Y. Chen, X. Wang, J. Zhang, C.Q. Bian, S.X. Pan, F. Chen, X.J. Meng, X.M. Zheng, X.H. Gao, F.S. Xiao, Catal. Today 258 (2015) 190-195.

[174] Y.W. Jiang, L. Zhang, Y.Q. Xie, S.C. Han, Q.Y. Zhu, X.J. Meng, ES. Xiao, Catal. Today 355 (2020) 476-481.

[175] P. Pornsetmetakul, N. Maineawklang, A. Prasertsab, S. Salakhum, E.J.M. Hensen, C. Wattanakit, Chem. Asian J. 18 (2023) e202300733.

[176] Z.M. El-Bahy, А.1. Hanafy, S.M. El-Bahy, J. Environ. Chem. Eng. 7 (2019) 103117.

[177] H. Chen, R. Zhang, W. Bao, H. Wang, Z. Wang, Y. Wei, Catal. Today 355 (2020) 547-554.

[178] A. Kumar, A. Saxena, A. De, R. Shankar, S. Mozumdar, RSC Adv. 3 (2013) 5015-5021.

[179] N.R. Mathe, S.S. Nkosi, D.E. Motaung, M.R. Scriba, N.J. Coville, Electrocatalysis-Us 6 (2015) 274-285.

[180] Z.Y. Chen, J.X. Mao, R.X. Zhou, Appl. Surf. Sci. 465 (2019) 15-22.

[181] A. Kumar, V.P. Kumar, A. Srikanth, V. Vishwanathan, K.V.R. Chary, Catal. Lett. 146 (2016) 35-46.

[182] H.X. Jiang, Z.H. Liu, C.X. Yao S Wang, Microporous Mesoporous Mater. 335 (2022) 111842.

[183] D. Xu, J. Yin, Y. Gao, D. Zhu, S. Wang, ChemPhysChem 22 (2021) 1287-1301.

[184] X.M. Gu, В. Zhang, H.J. Liang, Н.В. Ge, H.M. Yang, Y. Qin, J. Fuel Chem. Technol. 45 (2017) 714-722.

[185] S.S. Huang, D.Y. Yang, Q.X. Tang, W. Deng, L. Zhang, Z.Y. Jia, Z.F. Tian, О. Gao, L.M. Guo, Microporous Mesoporous Mater. 305 (2020) 110292.

[186] К. Li, Z. Li, L. Chen, Y. Dong, S. Ma, Е. Yuan, Y. Zhu, Catal. Sci. Technol. 7 (2017) 4984-4995.

[187] ©. Zhang, S. Gao, J. Yu, Chem. Rev. 123 (2022) 6039-6106.

[188] H.Y. Zhang, B.Y. Wang, W.F. Yan, Green Energy Environ. 9 (2023) 792-801.

[189] W.M. Liu, J.X. Tao, Y.H. Zhao, L. Ren, С. Li, X.F. Wang, J. Chen, J.Q. Lu, D.S. Wu, H.G. Peng, J. Catal. 413 (2022) 201-213.

[190] T. Dong, W.M. Liu, M.D. Ma, H.G. Peng, S.Y. Yang, J.X. Tao, C. He, L. Wang, P. Wu, T.C. An, Chem. Eng. J. 393 (2020) 124717.

[191] WM. Liu, S.Y. Yang, Q.L. Zhang, T.Y. He, Y.W. Luo, J.X. Tao, D.S. Wu, H.G. Peng, Appl. Catal. B Environ. 292 (2021) 120171.

[192] H.X. Chen, R.D. Zhang, H. Wang, W.J. Bao, Y. Wei, Appl. Catal. B Environ. 278 (2020) 119311.

[193] Q.L. Zhang, W.K. Su, P. Ning, X. Liu, H.M. Wang, J. Hu, Chem. Eng. Sci. 205 (2019) 230-237.

[194] T.L. Cui, W.Y. Ke, W.B. Zhang, Н.Н. Wang, X.H. Li, J.S. Chen, Angew. Chem., Int. Ed. 55 (2016) 9178-9182.

[195] L. Wang, С. Wang, J. Zhang, С. Bian, X. Meng, F.-S. Xiao, Nat. Commun. 8 (2017) 15240.

[196] R. Yan, S. Lin, Y. Li, W. Liu, Y. Mi, C. Tang, L. Wang, P. Wu, H. Peng, J. Hazard. Mater. 396 (2020) 122592.

[197] T. Sano, M. Itakura, M. Sadakane, J. Jpn. Petrol. Inst. 56 (2013) 183- 197.

[198] J. Zhang, L. Wang, Y. Shao, Y.O. Wang, B.C. Gates, ES. Xiao, Angew. Chem., Int. Ed. 56 (2017) 9747-9751.

[199] $. Goel, S.I. Zones, E. Iglesia, J. Am. Chem. Soc. 136 (2014) 1528015290.

[200] W.J. Sun, Z.L. Yang, Y.B. Xu, Y.W. Shi, Y.J. Shen, G.Z. Liu, RSC Adv. 10 (2020) 12772-12779.

[201] Е. Ribeiro, J.M. Silva, E. Silva, М.Е. Vaz, F.a.C. Oliveira, Catal. Today 176 (2011) 93-96.

[202] I. Marin, E. Adrover, D. Vega, M. Urbiztondo, М.Р. Pina, К. Mallada, J. Santamar, Green Process. Synth. 1 (2012) 169-174.

[203] У.Е. Yang, Z.H. Zhou, X.Y. Chu, X.J. Tang, M. Zhou, W. Zhou, T. Fu, Mater. Des. 219 (2022) 110744.

[204] J.R. Theis, J.A. Ura, Catal. Today 360 (2021) 340-349.

Footnote

* Corresponding author. Present address: Department of Environmental Engineering, School of Energy and Environmental Engineering, University of Science and Technology Beijing, Beijing, 100083, China.

E-mail address: [email protected] (Q. Yu).