Recent Advances in Aromatic Hydroxylation to Phenol and Hydroquinone Using H2O2

Abstract

Direct hydroxylation of aromatics and phenol processes using green oxidants plays an important role in the petrochemical industry. High selectivity towards hydroquinone is usually hard to achieve due to catechol formation and catalyst deactivation. Herein, we showed the recent studies devoted to selective phenol hydroxylation via oxidation using H₂O₂. This review summarizes progress that has been achieved in this area. Briefly, aromatic hydroxylation on heterogeneous catalysts, phenol hydroxylation on Ti-containing and supported catalysts, photocatalytic hydroxylation, and new approaches toward phenol hydroxylation have been reviewed.

1. Introduction

Phenol hydroxylation is a useful reaction for producing hydroquinone (HQ) and catechol (CAT), which are the key intermediates for a variety of fine chemicals, such as the flavor ingredient vanillin [1]. Cosmetics, paints, adhesives, and rubber, among others, where it is utilized as an antioxidant, intermediate, polymerization inhibitor, and photosensitive chemical [2]. As these industries experience growth, the global HQ market is expected to expand significantly in the forecast period (Figure 1). Furthermore, hydroquinone and its derivatives can be synthesized through the oxidation of various phenols [1]. The global hydroquinone market, in terms of volume, was approximately 81 thousand tons in 2023 and is anticipated to grow at a compound annual growth rate of 4.2% during the forecast period until 2034 [1,3,4]. With the expansion of these industries, the global hydroquinone market is projected to grow significantly in the coming years. Due to its significance in these applications, the global hydroquinone market is projected to reach approximately 130,000 tons by 2034 [3].

There are currently four main manufacturing processes for hydroquinone: oxidation of diisopropylbenzene or bisphenol A, hydroxylation of phenol, and oxidation of aniline (Figure 2) [1,5,6,7]. In the first route, the para-isomer is first isolated and then oxidized using oxygen to form the corresponding dihydroperoxide, which is subsequently treated with sulfuric acid to yield acetone and hydroquinone. In the phenol hydroxylation method, hydrogen peroxide acts as the hydroxylating agent, with strong mineral acids or ferrous or cobalt salts serving as catalysts [8]. In the aniline oxidation process, aniline is oxidized with manganese dioxide and sulfuric acid to form benzoquinone, which is then reduced to hydroquinone using either iron dust and water or catalytic hydrogenation [1]. The hydroxylation of phenol to hydroquinone, however, presents challenges in terms of selectivity and efficiency [1]. Achieving high selectivity for hydroquinone while avoiding the formation of byproducts like catechol (1,2-dihydroxybenzene) is a key objective. Traditional methods often require harsh conditions or environmentally hazardous reagents, emphasizing the need for greener and more efficient catalytic processes [9]. Utilizing hydrogen peroxide as an oxidant has shown promise due to its environmentally friendly nature, as it produces only water as a byproduct [10]. Thus, the development of efficient catalysts that can selectively convert phenol to hydroquinone using mild conditions and green oxidants is an active area of research with significant potential for sustainable chemical manufacturing.

Hydrogen peroxide (H₂O₂) is gaining attention as an ideal oxidant for the selective oxidation of aromatics to phenols. It is considered an environmentally friendly reagent due to its high oxygen content and its ability to decompose into water as a byproduct [10]. This minimizes environmental impact and eliminates the need for extensive purification steps. In the oxidation of aromatics, H₂O₂ provides a sustainable route to phenol production when paired with suitable catalysts, as it offers high atom efficiency and selectivity [11]. However, the use of H₂O₂ poses challenges due to its decomposition tendencies and the need for activation under controlled conditions [12].

Recent studies have focused on optimizing the reaction conditions and developing catalysts that can efficiently activate H₂O₂ for aromatic oxidation [12,13,14]. The choice of catalyst, solvent, and temperature significantly affects the reaction’s efficiency, selectivity, and yield. For instance, in some catalytic systems, the presence of acid or base additives is necessary to stabilize reactive intermediates and enhance H₂O₂ activation [12]. Furthermore, researchers have explored the use of various organic and inorganic co-catalysts to improve the performance of H₂O₂ as an oxidant in aromatic hydroxylation [10]. One of the major advantages of H₂O₂ is its ability to promote selective hydroxylation under mild conditions, thus reducing energy consumption and minimizing side reactions. However, achieving high selectivity and yield for phenols remains a challenge, as side products such as quinones and polyhydroxylated compounds can form [1]. Advances in catalyst design, including molecular and nanostructured catalysts, have shown the potential to overcome these limitations, enhancing both the selectivity and efficiency of aromatic oxidation processes using H₂O₂ [7].

The development of heterogeneous catalysts has played a crucial role in improving the efficiency of aromatic oxidation processes [15]. Heterogeneous catalysts, which consist of solid-phase materials that can be easily separated from liquid-phase reactants, offer several advantages, including recyclability, stability, and the ability to operate under continuous flow systems. These catalysts often incorporate metals such as iron, titanium, vanadium, and platinum, which are known for their ability to activate H₂O₂ and promote hydroxylation reactions [16,17,18,19,20]. Metal oxides, zeolites, and supported metal nanoparticles are some of the common forms of heterogeneous catalysts used in these reactions [15,21].

Three main industrial methods are currently utilized for the production of hydroquinone and catechol from phenol: the Rhone-Poulenc, Brichima, and Enichem processes [22,23,24,25]. These involve the hydroxylation by hydrogen peroxide, each using different catalytic systems. The Rhone-Poulenc method employs a homogeneous acidic catalyst, such as HClO₄ or H₃PO₄, while the Brichima process utilizes a Fenton reagent, specifically Co(II) and Fe(II). In contrast, the Enichem process employs a TS-1 catalyst. Enichem’s facility in Ravenna, Italy, commissioned in 1986, has an annual capacity of 10,000 tons of hydroquinone and catechol. The Enichem process operates at 90–100 °C with a phenol-to-hydrogen peroxide molar ratio of 3 and a TS-1 catalyst concentration of 3%. Compared to methods using homogeneous catalysts, the heterogeneous TS-1 catalyst in Enichem’s process achieves a higher phenol conversion of 25 mol%, compared to 5 mol% for Rhone-Poulenc and 10 mol% for Brichima. Additionally, the overall selectivity toward hydroquinone and catechol from consumed phenol is high at 90 mol% for the Enichem process, matching the Rhone-Poulenc process and surpassing Brichima’s 80 mol%. In terms of product ratio, the Enichem process produces catechol and hydroquinone at a 1:1 ratio, compared to a 1.4 ratio for Rhone-Poulenc and a variable ratio in the Brichima process.

Iron-based catalysts, for example, have been extensively studied for benzene hydroxylation due to their high activity and relative abundance [14]. Modified iron oxides or iron-containing zeolites have shown promise in enhancing the selectivity and conversion rates for phenol production. Similarly, titanium dioxide (TiO₂) and vanadium-based catalysts have been explored for their ability to activate H₂O₂ efficiently, often showing good performance under mild reaction conditions [13]. Zeolite-based catalysts, such as Fe-ZSM-5, have demonstrated excellent performance in aromatic oxidation due to their microporous structures, which facilitate the diffusion of reactants and products while providing active sites for H₂O₂ activation [26]. Nanostructured catalysts, including metal-organic frameworks (MOFs) and carbon-based materials doped with metals, are also emerging as promising candidates for efficient aromatic oxidation [27]. These catalysts offer the advantage of high surface area, tunable pore sizes, and the ability to design active sites at the molecular level, which can significantly improve the selectivity and activity of the oxidation process.

Recent advances in catalyst design focus on optimizing the interaction between the aromatic substrate and the catalyst surface to enhance the selectivity for phenols. Additionally, studies are being conducted to understand the role of various supports and promoters that can stabilize active sites, prevent catalyst deactivation, and enhance H₂O₂ utilization [7,8,10,12]. As the field progresses, the development of robust and recyclable heterogeneous catalysts remains a key focus, aiming to achieve high-efficiency, low-cost, and environmentally friendly processes for phenol production.

2. Production of Phenols via Direct Hydroxylation of Benzene

In recent years, the global phenol market has exhibited significant regional variability, driven by differing levels of demand and profitability across various parts of the world. In North America and Europe, phenol consumption has demonstrated a steady upward trajectory, while in Asia, the demand remains on a robust growth path. Projections suggest that by 2025, global phenol production could reach approximately 15.2 million tons annually [28]. This sustained growth is largely attributed to the increasing need for bisphenol A and phenolic resins, which are major downstream applications of phenol. With an anticipated annual growth rate of around 3%, it is evident that the worldwide demand for phenol remains substantial and continues to rise consistently [8].

Phenols are a crucial class of compounds widely used in the chemical industry due to their diverse applications. They serve as key intermediates in the synthesis of pharmaceuticals, agrochemicals, polymers, and fine chemicals. Phenolic compounds are essential for the production of resins, such as bisphenol A and phenolic resins, which are used in adhesives, coatings, and plastics. Moreover, phenols play a vital role in the synthesis of active pharmaceutical ingredients, including drugs with analgesic, anti-inflammatory, and antipyretic properties. The high demand for phenols in various industries makes their production a subject of ongoing research and development [29].

Traditionally, phenols are produced through processes such as the cumene method, which involves multiple steps and the use of hazardous reagents, leading to potential environmental and safety concerns. Additionally, these methods often result in low selectivity and efficiency, making it challenging to scale up production sustainably [7,28]. As the chemical industry seeks greener and more efficient routes for chemical synthesis, developing novel methods for phenol production has become a critical area of research. This is where the oxidation of aromatics presents a promising approach, particularly when using environmentally friendly oxidants such as hydrogen peroxide (H₂O₂). The use of H₂O₂ not only enhances the selectivity for phenol production but also minimizes waste, aligning with the principles of green chemistry [12]. Although hydrogen peroxide is currently more costly than molecular oxygen, it offers the significant advantage of being more readily activated under mild conditions with a broad array of catalysts. Moreover, these mild operating conditions enable the use of simpler and more cost-effective equipment in H₂O₂-based processes. This makes H₂O₂ a preferred oxidant, particularly in the synthesis of fine chemicals, where efficiency and controlled reaction conditions are crucial [30].

The direct hydroxylation of benzene to phenol has garnered significant interest as a potential route for phenol synthesis due to its simplicity and reduced dependence on acetone market fluctuations [28,29]. This single-step process offers advantages in terms of efficiency and sustainability. Nitrous oxide has demonstrated high phenol selectivity at elevated temperatures; however, its limited availability restricts broader applicability [22]. Alternatively, air or molecular oxygen is abundant and accessible, but the catalytic efficiency for these oxidants remains insufficient for industrial-scale operations [30]. Among available oxidants, hydrogen peroxide stands out due to its simplicity, environmental friendliness, and water as the sole byproduct. Despite these advantages, industrial adoption is hindered by low hydrogen peroxide utilization efficiency and limited phenol yields [31]. There is a growing focus on designing environmentally friendly and highly effective heterogeneous catalysts to facilitate benzene hydroxylation using hydrogen peroxide. Transition metals such as Fe, Cu, and V have been extensively explored for this purpose [28,29,31]. Additionally, other metals, including Co, Mn, Ni, Cr, and Mo (Table 1), have also shown catalytic activity for benzene hydroxylation, offering potential pathways for improved performance and efficiency [31].

To improve catalytic efficiency and enable catalyst recycling, active metal oxide or metal ion species are typically dispersed on high-surface-area supports or incorporated into the framework of zeolites [28,32,33,34,35]. The choice of catalyst support plays a critical role in designing highly effective catalysts, as catalytic performance is strongly influenced by the support’s characteristics, particularly its hydrophilic or hydrophobic nature and its interaction with active catalytic sites, benzene as the reactant, and phenol as the product [15].

Given the relatively limited range of active catalytic species and the wide variety of available supports, as well as diverse synthesis methods, attention has been focused on supports such as silica, carbon-based materials, and metal oxides [28,29]. These supports are commonly employed in conjunction with active species like Fe, V, Cu, and Ti to create catalysts (Table 1) with enhanced activity and selectivity for benzene hydroxylation to phenol [8,36,37,38,39].

Barbera and colleagues observed that phenol selectivity improves as the crystal size of Titanium Silicalite-1 (TS-1) decreases [40]. This improvement is attributed to the reduced residence time of phenol within the TS-1 pores, which minimizes its transformation into hydroquinone and benzoquinone. Consequently, smaller TS-1 crystallites enhance phenol selectivity. Bhaumik et al. introduced a solvent-free three-phase (solid–liquid–liquid) system for benzene oxidation, comprising a solid TS-1 catalyst, the organic substrate, and hydrogen peroxide [41]. Compared to the conventional two-phase system, which employs a co-solvent to homogenize the organic and aqueous layers, the three-phase system demonstrated a 15–25-fold increase in reaction rate. In the TS-1/H₂O₂ system, the presence of solvents leads to a prolonged induction period, whereas this period is nearly absent under solvent-free conditions. Under optimized conditions, the solvent-free system achieved a hydrogen peroxide utilization efficiency of approximately 85 ± 5 mol%, a phenol yield of 37.2%, and a phenol selectivity of 90.4%, significantly outperforming the two-phase system in both efficiency and selectivity.

Several studies on Ti- or V-containing MCM-41 reported decent activity; however, they showed poor H₂O₂ efficiency [41,42,43,44]. Bianchi and colleagues demonstrated the first heterogeneously catalyzed reaction for phenol production using TS-1 as a catalyst [43], achieving a phenol selectivity of 94%, with 8.6% conversion and 80.5% hydrogen peroxide selectivity. Notably, they introduced sulfolane as a solvent in this reaction, which played a critical role in enhancing phenol selectivity. The increased selectivity was attributed to the complex formation between sulfolane and phenol, which improved the reaction efficiency and minimized undesired side reactions. Efforts to enhance benzene conversion have utilized catalysts such as V-functionalized MCM-41, LaMn-MCM-41, Co(V, Nb, La)-MCM-41, and Fe/activated carbon, achieving benzene conversion rates between 50–65% and hydrogen peroxide selectivity ranging from 17–50% (Table 1). Recent advancements highlight the use of innovative catalytic materials, including vanadyl pyrophosphate, vanadium phthalocyanine complexes, vanadium-loaded SBA-16, and vanadium-containing aluminum phosphate molecular sieves, showcasing their potential applications in this reaction (Table 1). Table 1

Representative examples of heterogeneous catalysts of direct hydroxylation of benzene to phenol.

Catalyst	Temperature (°C)	Conversion (wt. %)	Selectivity (%)	Reference
TS-1	60	29	95	[41]
Ti-grafted/MCM-41	65	92	95	[42]
TS-1B	100	9	94	[43]
TI-MCM-41	60	>70	100	[39]
Si-TiMCM-41	60	18.7	90	[44]
CuO/SBA-15	65	20.6	92.4	[45]
CuO/KIT-6	65	11.7	85.0
Cu-polymers	70	7	>99	[46]
Ni-polymers	70	5	>99
Cu/MCM-41	RT	21	94	[47]
Nb//MCM-41	70	19.4	84.5	[48]
Fe/Al2O3	60	12	100	[49]
FeSO4/SiO2	70	14	100	[50]
Fe/C	63	50	40	[51]
Fe/MgO	60	36	100	[52]
Fe/TiO2	30	15	18	[53]
Pt-Fe/TiO2	30	6.5	91	[36]
Pd-Fe/TiO2	30	6.7	80
Co-Fe/TiO2	30	3.3	58
Ni-Fe/TiO2	30	3.0	56
Cu-V/TiO2	60	28	90	[38]
Fe/V/Cu/TiO2	30	15	49	[54]

The hydroxylation of benzene to phenol is a prominent research focus due to the demand for efficient, one-step production routes. Among various oxidants, hydrogen peroxide (H₂O₂) is particularly advantageous because it produces water as the sole byproduct, making the process environmentally friendly and economical. However, the direct hydroxylation of benzene using H₂O₂ faces challenges due to low selectivity and efficiency. To address these, various heterogeneous catalysts have been developed, notably those based on transition metals like Fe, Cu, V, and Ti, which are embedded within high-surface-area supports like silica, carbon, and metal oxides. Titanium silicalite-1 (TS-1) has demonstrated promising results in benzene hydroxylation with high phenol selectivity, which improves as the catalyst’s crystal size decreases, reducing contact time and minimizing over-oxidation to byproducts like hydroquinone and benzoquinone. Other successful catalysts include vanadium-functionalized supports such as VO₂/MCM-41 and metal-doped MCM-41 variants, showing conversion rates of 50–65% and H₂O₂ selectivity up to 50%. Innovative methods such as solvent-free systems and the application of mixed-metal or metal-ion-doped supports aim to enhance reaction rates and selectivity. Additionally, patents highlight the potential of vanadyl pyrophosphate and vanadium-containing molecular sieves, which offer stable, recyclable, and potentially industrially viable catalysts. These studies indicate ongoing efforts to develop selective, efficient, and sustainable catalysts for benzene hydroxylation in green chemistry frameworks.

3. Hydroxylation of Phenol on Ti-Containing Molecular Sieves

In the hydroxylation of phenol using hydrogen peroxide, the most commonly used titanium silicate catalysts include zeolites containing titanium in their structure [15,55,56,57]. Hydroxylation, with the most studied example—TS-1, is typically performed at temperatures ranging from 50 to 90 °C, with a phenol-to-hydrogen peroxide molar ratio between 2:1 and 8:1 and a catalyst concentration of 0.8–2.0 wt. %. Reaction times span 0.5 to 6 h and may proceed with or without solvents [15]. Common solvents for this process include water, methanol, ethanol, acetone, and acetonitrile. The resulting molar ratio of catechol to hydroquinone in the product mixture is usually around 1, while the formation of tar byproducts varies up to 20%.

Research on TS-1 catalysts has demonstrated that an increase in titanium content within the catalyst structure correlates with higher phenol conversion, while the hydroquinone-to-pyrocatechol ratio remains largely unaffected by titanium concentration [9]. Studies examining the impact of catalyst concentration indicate that higher concentrations enhance phenol conversion; however, at lower catalyst concentrations, notable quantities of para-benzoquinone are formed. Investigations into the influence of reaction time revealed that within the first six hours (with experiments spanning 1 to 20 h), the reaction mixture prominently features p-benzoquinone formation [9,18].

The studies on solvent effects indicate that, regarding phenol conversion, acetone and methanol yield the most favorable outcomes [8]. Protic solvents, such as methanol, tend to promote hydroquinone formation, whereas aprotic solvents, like acetone, favor catechol production (Figure 3). For TS-1, in all solvents tested, hydroquinone is predominantly formed at titanium sites located on the internal surfaces, indicating that the reaction occurs primarily within the TS-1 pore structure [9]. Additionally, experiments with Ti-BEA in methanol revealed a similar preference for hydroquinone formation, even though the larger pores in Ti-beta can accommodate bulkier intermediates that would otherwise contribute to catechol synthesis [9]. This suggests that methanol’s solvent properties may play a key role in directing product selectivity, even in catalysts with varying pore sizes.

The studies on the heterogeneous phenol hydroxylation indicate that the effect of solvent is a rather complex issue, and there is no direct correlation between the solvent and the product distribution. However, only in methanol solution can the hydroquinone-to-catechol ratio reach more than 2 (Figure 3). It is known that the process mechanism of phenol hydroxylation is dependent on the solvent [15]. It is believed that the main reason lies in various hydroperoxo-titanium complexes, which are formed depending on the solvent (Scheme 1).

It is proposed that when protic solvents, such as alcohols and water, are present, their molecules coordinate with the peroxo group on the active titanium site to form a larger, pentacoordinated intermediate complex that is stabilized by hydrogen bonding. A five-membered ring between alcohol and peroxo group at the titanium species has been determined as the active site for a TS-1-catalyzed process. When phenol is hydrogen-bonded to the solvent’s OH groups, it approaches the bulky titanium site with its OH group oriented away from titanium (as illustrated in Scheme 2), leading to hydroquinone formation. Furthermore, the proximity of coordinated protic molecules near the peroxo group may facilitate hydrogen bond formation at the active site, weakening the H-bond with the phenol molecule and thereby promoting ortho-hydroxylation. Aprotic solvents such as acetone or acetonitrile cannot form stable peroxocomplexes with the titanium species. Therefore, the formation of those complexes is limited. In that case, another reaction pathway is opened, such as the hydroxylation via the pentacoordinate Ti site, involving the coordination of phenol to Ti-peroxo species (Scheme 3).

In aprotic solvents, on crystal surfaces, or within molecular sieves with wide pores, pyrocatechol is likely to be the favored product. Due to the elevated exposure of titanium sites on crystal surfaces to concentrated hydrogen peroxide, a secondary –OOH group can potentially form on the same titanium atom [58].

The studies on the effect of temperature on the process demonstrate that the formation of para-benzoquinone, which is significant at low temperatures, becomes negligible above 40 °C [58,59,60]. The temperature effect on conversion is usually higher in acetone than in methanol. Catechol remains the primary dihydroxybenzene across all temperatures when using acetone as the solvent, whereas, in methanol, it is the dominant product only at temperatures below 70 °C [58]. Research on the impact of reactant molar ratios indicates that phenol conversion rises with an increased molar ratio of the reactants, while the hydroquinone-to-catechol ratio remains largely unaffected by changes in this ratio [58,59,60].

Similar findings have been demonstrated for the other titanium-containing catalysts [21,61]. It has been observed that TS-1 and TS-2 exhibit comparable activity in phenol hydroxylation, provided they share equivalent Si/Ti ratios and crystal dimensions. Studies on the aluminum-free Ti-Beta catalyst indicate that TS-1, with its smaller pore size (0.56 × 0.54 nm compared to Ti-Beta’s 0.76 × 0.64 nm), results in reduced phenol conversion but enhanced selectivity for hydroquinone. Hydroquinone formation is favored within TS-1 pores, while product distribution on the external crystal surfaces is strongly solvent-dependent. Catechol formation is preferential in acetone, whereas hydroquinone production is enhanced in protic solvents. In mixed methanol–water systems, the highest phenol conversion is observed in pure water, while the optimal hydroquinone-to-catechol molar ratio (approximately 2.5) occurs at the lowest water concentration.

The oxidation of large molecules on TS-1 catalysts is often hindered by mass transfer limitations, which can substantially reduce catalytic efficiency [62]. While much of the literature focuses on the oxidative properties of TS-1 titanosilicate, relatively few studies address these mass transfer issues, despite their potential to significantly affect catalyst performance. Additionally, previous studies have primarily modeled mass transfer behavior for spherical catalyst particles, though molecular sieve crystals rarely exhibit such shapes [15,63]. Although a solution for diffusion challenges in non-spherical particles was developed [64], practical applications of this approach in real catalytic processes remain unreported. For catalyst particles with rectangular parallelepiped geometries, the equation describing the relationship between the effectiveness factor (η) and the Thiele modulus (φ) is illustrated in Figure 4.

Using these models, it is possible to plot the efficiency factor as a function of the Thiele modulus for parallelepipeds of varying dimensions. Figure 5 shows η plotted against φ for TS-1 samples with different parallelepiped configurations, with curve 3 representing spherical particles for comparison. From Figure 5, it is evident that particle shape significantly impacts the effectiveness factor relative to the Thiele modulus. This effect is clear when comparing spherical particles (curve 3) to parallelepiped particles (curve 1). Moreover, differences in the aspect ratios of similarly shaped particles further influence the effectiveness factor, as seen in the comparison of curves 1 and 2.

Ti-MWW is one of the most recent titanium silicalite catalysts that have been developed. Its structure originates from a layered precursor that undergoes dehydroxylation during calcination, resulting in stable layers. In addition to the two-dimensional sinusoidal channels with 10-membered rings (0.4 × 0.5 nm) running parallel to the ab-plane, the MWW framework also features a secondary channel system, which includes large supercages measuring 0.7 × 0.7 × 1.8 nm. These supercages open into pocket-like structures of 0.7 × 0.7 nm on the crystal surface (18). Due to its unique lamellar structure, Ti-MWW is anticipated to exhibit catalytic activity comparable to that of TS-1 (Table 2). Additionally, its synthesis is more reproducible, and it demonstrates greater structural stability [58,66].

One way to improve diffusion is to develop the microporous structure of titanium silicate molecular sieves. In [71], Ti-YNU-2 was synthesized through post-synthetic stabilization of the defect-rich precursor YNU-2P, utilizing Si migration during mild steam treatment, followed by vapor-phase treatment with TiCl₄. This Ti-YNU-2 catalyst demonstrated markedly higher activity and selectivity than the traditional microporous Ti-MCM-68 catalyst, which itself surpasses TS-1 in performance for phenol oxidation with H₂O₂ as an oxidizing agent. The high catalytic efficiency and para-selectivity of Ti-MSE materials (such as Ti-MCM-68 and Ti-YNU-2) are attributed to enhanced diffusivity within their 12-ring channels compared to the 10-ring channels, along with the absence of substantial cavities at the 12/10R intersections. Beyond these shared features, Ti-YNU-2 exhibits unique properties; its significant site defects at particular T sites may enable the formation of a more precisely defined transition state, surpassing the traditional size restriction mechanism governed by simple molecular confinement (Figure 6). These results revealed that Ti-YNU-2 had a much greater tendency to generate active Ti-OOH species than TS-1 and Ti-MCM-68, and this could explain the remarkably enhanced activity of Ti-YNU-2.

Another way to increase the activity of Ti-microporous molecular sieves is to create a high external catalyst surface. In [56], the authors developed a meso-macro hierarchical porous structure via a post-treatment method using a basic TPAOH aqueous solution. The dissolution of the TS-1 framework occurred predominantly in areas with structural defects, where OH- ions attacked silanol groups both within the crystal and on its external surface. This process created intracrystal mesopores and macropores that extended to the crystal’s surface. Compared to the untreated TS-1 zeolite, phenol hydroxylation activity over TS-1 that was post-treated with TPAOH improved when the TPAOH solution’s alkalinity was moderate or low, while activity decreased significantly when the solution was highly alkaline. The variations in catalytic performance between post-treated TS-1 zeolites and pristine TS-1 were attributed to a combination of changes in textural properties, hydrophobicity, and titanium content within the framework.

It is essential to design more effective and durable ordered mesoporous silica materials with titanium incorporated into their framework to facilitate the transformation of bulky organic molecules relevant to pharmaceutical applications. The problem can be solved by replacing microporous sieves with structured mesoporous titanosilicates with pores from 2 to 50 nm and a high specific surface area [72,73,74]. Their textural and acidic properties can be controlled both at the synthesis stage and by modifying the finished materials. Among the mesoporous titanosilicates, the most studied are Ti-SBA-15, Ti-MCM-41, Ti-HMS, and Ti-MTS-9, which have pores from 50 to 80 Å and whose synthesis is carried out under mild conditions in an aqueous medium without the use of organic solvents (Table 2). In [55], the process of hydroxylation of phenol was studied in the presence of two distinct types of titanosilicates: Ti-SBA-12 and Ti-SBA-16. These materials were compared to TS-1 and Ti-MCM-41. Both Ti-SBA-12 and Ti-SBA-16 were found to be highly active catalysts, but their activity was lower than that of TS-1. However, they were still more active than the other mesoporous materials, such as Ti-MCM-41 and Ti-SBA-15. The only products of the phenol hydroxylation reaction were catechol and hydroquinone. The para-selective hydroxylation occurred predominantly on Ti-SBA-12 than on TS-1 or Ti-SBA-16.

4. Hydroxylation of Phenols on Supported Metal Catalysts

Currently, various heterogeneous catalysts containing different metals are employed for phenol oxidation in the presence of hydrogen peroxide [11,75,76,77]. A common approach involves using an excess of phenol relative to the oxidant to prevent excessive oxidation of the desired products. The introduction of alkyl or alkoxy groups on the phenol molecule activates the aromatic ring and stabilizes the resulting quinones against further oxidation, enabling high selectivity for quinones even at substantial substrate conversions [30].

It was mentioned above that TS-1 was among the most extensively studied and effective heterogeneous catalysts for phenol hydroxylation with H₂O₂, though other heterogeneous catalysts also facilitate this reaction [1,56,62,78,79,80,81]. These alternatives include germanozeosilicates, stanno- and zirconozeosilicates, and titanium oxide [82,83,84,85,86]. Additionally, catalysts that operate via intrinsic acidities, such as acidic clay, bridged clay, zirconium phosphates in acetic acid medium, and vanadium(V)- or Ti(IV)-exchanged Nafion resin, offer selective, though low-yield, access to hydroquinone [87,88,89,90]. Metal cation-exchanged HZSM-5 may also selectively and quantitatively produce hydroquinone, though none of these catalysts have yet been adopted for industrial use [91].

Various supported heterogeneous catalysts have been explored for this reaction as well, including nickel(II) and iron(II) complexes, vanadium-silicate molecular sieves, Ni(II) and Cu(II) coordination polymers, CoNiAl hydrotalcite, vanadium-substituted Keggin heteropoly acids, hollow titanium silicalite zeolites, copper nanoparticles, Fe-ZSM-5 zeolites, and Fe- and Co-loaded mesoporous MCM-48 [17,19,20,26,37,46,92,93,94,95]. Efforts to enhance catalytic efficiency have included introducing diverse transition metals to create active sites in supported heterogeneous catalysts [30,57,96,97,98,99,100,101,102,103]. Zhang et al. synthesized Cu-MCM-41 using a surface organometallic chemistry method, achieving a 38% phenol conversion rate with 65% selectivity for dihydroxybenzenes [104]. Jiang et al. noted that Fe-MCM-41 nanoparticles with shorter mesoporous channels and active Fe species showed accelerated reactant mass transfer, achieving 22% phenol conversion with a reduced induction period [105]. Wu et al. examined Fe-MCM-41 catalysts with varying iron contents, reporting 25.3% phenol conversion and 78.4% selectivity to dihydroxybenzenes for Fe-MCM-41 with a Fe/Si molar ratio of 0.091 at ambient conditions [106]. It was found that the reaction pathway involves the generation of ·OH radicals by the decomposition of H₂O₂ via a redox cycling of Fe³⁺/Fe²⁺ (Figure 7).

Shen et al. reported a successful synthesis of Fe-containing catalysts using an ion exchange technique over hierarchically porous ZSM-5 [91]. The results showed that Fe-M-ZSM-5 demonstrated a phenol conversion of 42.3% with selectivity to dihydroxybenzenes—92.5%, whereas Fe-ZSM-5/MCM-41 showed 46.2% phenol conversion and 90.1% dihydroxybenzenes selectivity. The recyclability tests revealed that Fe-ZSM-5/MCM-41, with an ordered mesoporous structure and bigger surface area, had better anti-deactivation performance than microporous Fe-ZSM-5.

The team of Prof. Quintanilla showed the possibility of Fe-MOF application in the direct hydroxylation of phenol [27]. The semi-batch catalytic performance using Fe-BTC nanopowders resulted in a high conversion of phenol (54%) and selectivity towards dihydroxybenzenes (65%).

Copper-based transition metal complexes have been widely applied as catalysts in phenol hydroxylation reactions. While other d-metal-based catalysts promote side reactions, often producing by-products like quinones and high-molecular-weight tars, copper-based catalysts have been particularly researched for their performance [107,108,109,110]. Various copper-incorporated molecular sieves exhibit impressive catalytic efficiency in phenol hydroxylation. For instance, Wang et al. developed a synthetic protocol for the one-pot crystallization of Cu-SBA-15, where Cu was incorporated in the amorphous silica structure under acidic conditions [107]. The substituting Cu²⁺ was incorporated into the silica framework, forming a new type of active site, which increased the phenol conversion to 62.4% and the diphenols selectivity to 97%. The Cu-SBA-15 had higher activity compared to that of the microporous titanium silicalite zeolite TS-1 (47.1% phenol conversion and about 50% selectivity to CAT under the same reaction conditions). Additionally, Cu²⁺-exchanged zeolites such as HY, Hβ, USHY, NaY, and HZSM-5 have shown strong catalytic performance in phenol hydroxylation using hydrogen peroxide as the oxidant in a batch reactor under atmospheric conditions, proving more active than titanosilicate-based catalysts [82,111,112,113]. Other copper-based catalysts, including Cu/MCM-41, Cu/ZSM-5, and Cu/HMS, have also delivered promising catalytic activity [101,103,112,114]. Furthermore, Karakhanov et al. presented iron- and copper-based complexes with N,O and N,N ligands for phenol hydroxylation, showing remarkable selectivity for catechol under mild conditions [115].

In [116], Cu-containing macromolecules were synthesized and heterogenized on the surface of aminated SBA-15 molecular sieves. Copper-based macromolecular catalysts in homogeneous and heterogeneous forms were studied in the hydroxylation of phenolic compounds: anisole, benzene, and substituted phenols. The catalysts showed comparable conversion (65–72%) with the formation of ortho- and para-substituted products, and they showed comparable recyclability and reusability.

In [111], the zeolite-Y-encapsulated Cu(II) complex of 2-(2′-hydroxy-phenyl)benzimidazole was synthesized using the flexible ligand method. This catalyst demonstrated suitable activity and high selectivity towards CAT. It was determined that Cu-complexes in the reaction with H₂O₂ lead to the formation of three kinds of intermediates that are dominated by Cu-O interaction (Scheme 4). This intermediate transfers the coordinated oxygen atom to the substrates, initiating the formation of products. Thus, the catalytic performance of the encapsulated catalyst arises due to the formation of reversible intermediate hydroperoxide species.

In [117], hydroxylation of phenol was studied using less than 1% Cu-containing layered double hydroxides with different cobivalent ions like Mg, Zn, Ni, and Co, both in their as-synthesized and calcined forms. Zn-containing samples were the most active at low copper concentrations in both forms due to the facile formation of Cu⁺, an active intermediate for phenol hydroxylation.

Layered double hydroxide (LDH)-based catalysts have also been effectively utilized in phenol hydroxylation [118,119]. CuMgAl-LDH catalysts, prepared with varying Cu/Mg molar ratios, showed that the Cu²⁺ ion acts as the active species in the oxidation process [120]. Another set of Cu-LDH catalysts featuring different divalent ions like Mg, Zn, Ni, and Co was synthesized in both their native and calcined forms [117]. The LDH catalyst containing Zn ions at low copper concentration achieved optimal results, exhibiting 26% phenol conversion. Additionally, studies using CuMgAl-LDH@mSiO₂ nanosheets and Fe₃O₄@CuMgAl core–shell-structured magnetic nanocatalysts reported significantly higher catalytic activities than those observed with unmodified CuMgAl-LDH [121,122]. Furthermore, Cu-LDHs incorporating various rare earth dopants were tested for enhanced catalytic efficiency, with activity effects increasing in the order of Ce < Y < Sm < La [123]. Yusuf et al. explored V-intercalated CuMgAl-LDH prepared through ultrasonic-assisted co-precipitation and ion-exchange methods, demonstrating notable activity at 80 °C over 6 h with 50.2% phenol conversion and 57.26% selectivity toward catechol and hydroquinone [17].

Sun et al. developed a new type of catalyst, a Cu–Bi–V–O complex oxide, which was synthesized using a hydrothermal process [124]. The catalytic data for the hydroxylation of phenol using hydrogen peroxide indicated that this catalyst was comparable to TS-1. In addition, investigations using the ESR spin-trapping technique on the catalyst have suggested that Cu²⁺ ions are the main active sites, and hydroxyl radicals are believed to be the main active intermediates in the phenol hydroxylation process.

5. Photocatalytic Hydroxylation of Phenols

The production of essential chemicals and fuels through sunlight-driven heterogeneous photocatalysis stands as a critical goal in contemporary chemistry [125]. As a result, the development of innovative photocatalysts that can operate effectively under visible light and exhibit high performance under UV light—which constitutes merely 3% of solar radiation—has been extensively studied [125,126,127,128,129]. Although photocatalytic processes have been widely studied in various oxidation reactions, the phenol oxidation reaction has been mainly investigated as a model reaction for non-selective degradation in wastewater treatment [125,126]. Titanium dioxide (TiO₂) has been widely studied as a photocatalyst for wastewater treatment, and in particular for the degradation of phenols through oxidative degradation [130,131]. The most common form of this material is P 25, which is commercially available and consists of a roughly 75:25 ratio of anatase to rutile TiO₂ [132]. This TiO₂-containing catalyst has been extensively studied for photocatalytic application because of its low cost, non-toxicity, environmental friendliness, high chemical stability, and excellent catalytic activity [125,126]. Ye et al. described the possibility of improving the photocatalytic activity of TiO₂ by exposing {001} facets via the hydrothermal treatment of Ti(OC₄H₉)₄–HF–H₂O mixed sol-gel [133]. The study showed that photocatalytic oxidation of phenol and selectivity (yield) of catechol were positively correlated with the percentage of exposed {001} facets of the high-energy TiO₂ nanocrystals.

Despite advancements, two significant limitations hinder photocatalytic efficiency in real-world applications. First, photogenerated electron-hole pairs tend to recombine rapidly, reducing overall reaction efficiency; second, the wide band gap restricts absorption primarily to UV light rather than visible light, which limits effective sunlight utilization [134]. Various strategies, such as copper and nitrogen doping, have been implemented to address these issues [126,130]. To date, several TiO₂-based composites—such as CuO/TiO₂, NiO/TiO₂, MoS₂/TiO₂, TiO₂-F and BiVO₄/TiO₂—have been synthesized with improved photocatalytic performance [129,133,135,136,137,138]. In recent years, bismuth oxyhalides (BiOX, X = Cl, Br, I) have emerged as promising photocatalysts due to their unique layered structure, consisting of [Bi₂O₂] slabs interleaved by double halogen atom layers along the [001] direction [135,139,140,141]. Behera et al. reported a facile synthesis of mesoporous Bi₂O₃/TiO₂N_x nanocomposites using a template-free homogeneous co-precipitation technique [16]. The photocatalytic activities of those systems were evaluated in the hydroxylation of phenol under direct solar irradiation. The catalysts show excellent activity for selective diphenol production without using any oxidant. One of the photocatalytic nanocomposites demonstrated very high activity in a phenol conversion of 99% in aqueous medium with 100% selectivity towards hydroquinone. Although this catalytic results information was impressive, the current scheme was far from the pilot scale due to the low concentration of the substrate and overall catalytic power. Therefore, further investigation into this scheme is required.

Li et al. reported the development of BiOI/TiO₂ heterostructures by biomimetic synthesis and a simple hydrothermal method [134]. The photocatalytic activities of these structures were measured in the photocatalytic selective hydroxylation of phenol with high concentration under simulated solar light irradiation. The results demonstrated that the BiOI/TiO₂ heterostructure exhibited much higher activity compared to the pure TiO₂ and BiOI. After an irradiation time of 30 min, the phenol conversion was 13.5%, and selectivity towards diphenols was 92.1%, which can be ascribed to more light absorption and effective separation of photogenerated electrons and holes. It was further confirmed that p-n heterojunctions, narrow band gaps, and exposed reactive facets can contribute to enhanced photocatalytic performance. Based on the obtained results, a photocatalytic process mechanism and transfer process on BiOI/TiO₂ were suggested (Figure 8).

Additional studies have focused on the photocatalytic selective hydroxylation of phenol. For instance, Lv et al. reported a 20.1% yield of dihydroxybenzene (DHB) using a TiO₂/UV system, though the low phenol concentration (20 mg/L) limits its applicability for industrial purposes [142,143]. Ide et al. reported the synthetic procedure for TiO₂-supported Au nanoparticles for the oxidation of aqueous phenol to hydroquinone under sunlight irradiation [16]. Golden nanoparticles drastically decreased the amount of the surface titanol species and then promoted the desorption of the dihydroxybenzenes generated from the catalyst surface. Also, the presence of CO₂ enhanced the desorption of the product, which prevented overoxidation. The comparison of photoinduced and thermal oxidation of phenol over the TS-1 catalyst revealed that the effect of light intensity was less prominent as the temperature was above 60 °C [59]. In [60], the authors showed that the conversion of phenol was higher in the thermal process, whereas the product ratio of HQ/CAT was higher in the photocatalytic reaction.

6. New Trends in the Phenol Hydroxylation Process

There are many attempts to improve the present technology of HQ and CAT production, not just by tuning heterogeneous catalysts but also by finding new effective processes. Biological methods have recently developed many feasible processes and products, especially in the field of medicine and in the food industries [144,145]. Due to the fact that enzymes have high efficiency in catalyzing position-specific and stereospecific reactions, there were attempts to develop a microbial process for the hydroquinone production from phenol [146,147,148]. Yoshida and co-authors developed a laboratory-scale technology that consisted of three parts: biocatalyst production, the main reaction, and the downstream process [146]. Throughout the process, a production of 3.0 g·L⁻¹·h⁻¹ and a hydroquinone concentration of 2.2 g·L⁻¹ were achieved using Mycobacterium sp. B-394, and the selectivity towards HQ and the conversion of phenol remained almost quantitative. In the downstream process, concentration using a reverse osmosis method and crystallization at low temperatures were used. Experimental results suggested that HQ could be sufficiently recovered from the reaction mixture using these two steps.

Recent advancements in electrocatalysis for the hydroxylation of phenol to hydroquinone and catechol have introduced innovative techniques and materials aimed at improving efficiency and selectivity [149,150,151]. One key approach involves the use of advanced electrocatalysts, such as surface-modified carbonaceous electrodes and self-supported 3D porous structures like PbO₂ on carbon fiber substrates [152]. These modifications enhance active surface area, conductivity, and charge transfer, resulting in higher yields and selectivity for hydroquinone or catechol. For instance, the paired electrosynthesis approach utilizing PbO₂ electrodes has shown notable improvements in selectively producing 1,4-hydroquinone with minimized byproducts in a membrane-free setup. Another promising strategy employs iron-based metal-organic frameworks (MOFs), which offer high catalytic activity and stability under mild conditions. These catalysts facilitate efficient hydroxylation of phenol using hydrogen peroxide as the oxidant, achieving impressive yields and selectivity without requiring high temperatures or organic solvents [27].

In review [147], the authors pointed out that phenol hydroxylase facilitated the addition of a hydroxyl group at the ortho position of an aromatic ring, converting phenol into catechol. This process is mediated by an NADP-dependent flavin monooxygenase enzyme and represents the initial stage in the microbial breakdown of aromatic compounds. Monooxygenases incorporate one atom of molecular oxygen into the substrate, while the second oxygen atom is converted to water using a hydrogen donor unique to each enzyme. Beyond phenol, which is the enzyme’s primary substrate, phenol hydroxylase can also catalyze the hydroxylation of phenols with hydroxyl, amino, halogen, or methyl substitutions.

An effective approach to addressing the challenges described above involves integrating a heterogeneous catalytic reaction in a slurry with membrane separation, forming a structured membrane reactor [153,154,155]. This reactor concept leverages the selective permeability of membranes, which retain the catalyst while allowing reactants and products to pass through. Membrane reactors can be designed in two primary configurations: a submerged membrane reactor, which consolidates reaction and separation zones in a single unit, and a side-stream membrane reactor, where the reaction occurs in a stirred vessel while product separation is managed in a separate cross-flow membrane unit. The side-stream design offers greater flexibility and scalability due to the physical separation of reaction and separation zones, though it may result in more catalyst loss through piping and pumping and requires recirculation loops, increasing energy demand. Recent research has increasingly focused on submerged membrane reactors. In [154], phenol hydroxylation to dihydroxybenzene (DHB) catalyzed by ultrafine TS-1 served as a model to explore the continuous integration of catalytic reaction and membrane separation (Figure 9). A submerged ceramic membrane reactor system was developed for this purpose, with particular attention to the effects of operating conditions on phenol hydroxylation efficiency and membrane filtration properties.

7. Conclusions

The hydroxylation of phenol to hydroquinone and catechol is a significant reaction for producing dihydroxybenzenes, which are crucial intermediates in industries such as polymer synthesis, pharmaceuticals, and agrochemicals. Fundamentally, this reaction involves selective oxidation of phenol at specific sites, typically using hydrogen peroxide (H₂O₂) as the oxidant due to its environmental friendliness and high atom economy. Catalysts such as titanium silicalite (TS-1), iron-based complexes, and more recently, metal-organic frameworks (MOFs) have been extensively studied for their efficiency in driving this transformation under mild conditions. Recent studies have focused on employing various catalytic processes to enhance efficiency, selectivity, and sustainability. One common approach utilizes heterogeneous catalysts, with hydrogen peroxide (H₂O₂) as an oxidant. Catalysts such as titanium silicates and Fe- and Cu-based molecular sieves demonstrate high activity and selectivity for hydroxylating phenol to dihydroxybenzenes. Although these catalysts provide robust performance, they face challenges like mass transfer limitations and stability issues. Photocatalytic systems offer a sustainable alternative by using sunlight to drive hydroxylation. Catalysts such as TiO₂ and modified bismuth-based composites (e.g., BiVO₄/TiO₂) are tailored for enhanced light absorption under visible and UV light. However, electron-hole recombination remains a bottleneck, limiting their practical efficiency. Membrane reactor technology integrates catalyst retention and continuous product separation, which enhances the overall process. Submerged and side-stream reactor designs have been effectively used in phenol hydroxylation studies, with ultrafine TS-1 catalysts showing promising conversion rates. In addition, microbial oxidation presents a biologically driven route to hydroxylation, using enzymes like phenol hydroxylase for high selectivity towards hydroquinone. Although biocatalytic processes generally have slower reaction rates and pose scalability challenges, they are a green alternative, reducing reliance on chemical oxidants. Overall, these approaches provide unique advantages and limitations, collectively advancing phenol hydroxylation technology for potential industrial applications.

Author Contributions

Conceptualization, E.N. and A.M.; software, E.N.; formal analysis, D.R.; investigation, D.R.; data curation, E.N.; writing—original draft preparation, E.N.; writing—review and editing, E.N. and A.M.; visualization, M.A. and O.S.; supervision, A.M.; project administration, E.N.; funding acquisition, O.S. and E.N. All authors have read and agreed to the published version of the manuscript.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflicts of interest.

Footnotes

Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Figures, Schemes and Tables

Figure 1. (A) Worldwide HQ production. (B) Global HQ market in 2023 [1,3,4]. Adapted with permission from Ref. [1]. Copyright 2024 John Wiley and Sons.

Figure 2. The production technologies of HQ. I—oxidation of diisopropylbenzene and bisphenol A, II—hydroxylation of phenol, III—oxidation of aniline.

Figure 3. The effects of water and methanol solvents on the hydroquinone-to-catechol selectivity in the hydroxylation of phenol overall-free Ti-beta [9,18]. Reproduced with permission from Ref. [18]. Copyright 2024 Elsevier.

Scheme 1. Possible configurations of the hydroperoxo-titanium active site of TS-1: (A) Hexacoordinate octahedral; (B) pentacoordinate trigonal bipyramidal; (C) Tetracoordinate tetrahedral [15]. Reproduced with permission from Ref. [15]. Copyright 2024 Elsevier.

Scheme 2. Possible reaction mechanism for the formation of HQ via alcohol coordination to the Ti-active site [9,15]. Adapted with permission from Ref. [15]. Copyright 2024 Elsevier.

Scheme 3. Possible reaction mechanism for the formation of CAT in aprotic solvent [9,15,58]. Adapted with permission from Ref. [15]. Copyright 2024 Elsevier.

Figure 4. Efficiency factor as a function of Thiele modulus for the parallelepiped particle. Here η = rdif/rint—effectiveness factor, φ—Thiele modulus, β = a/b, δ = a/c—geometric parameters, and a, b, c—sides of parallelepiped, m, n, p = 0 … 100—parameters [65]. Reprinted with permission from Ref. [61]. Copyright 2024 MSU.

Figure 5. Plot of efficiency factor vs. Thiele modulus for the catalyst particles with various shapes: (1) parallelepiped, a × b × c = 25 × 7 × 4, (2) parallelepiped, a × b × c = 3 × 2.5 × 0.9, and (3) sphere [65]. Reprinted with permission from Ref. [61]. Copyright 2024 MSU.

Figure 6. Schematic illustration showing possible interactions between a phenol molecule and an active-state framework of Ti-YNU-2, including a Ti-OOH site and other site defects [71].

Figure 7. Reaction pathway of the hydroxylation of phenol on Fe-containing catalysts [106]. Adapted with permission from Ref. [106]. Copyright 2024 Elsevier.

Scheme 4. Proposed mechanistic pathway for phenol oxidation [111]. Reprinted with permission from Ref. [113]. Copyright 2024 Elsevier.

Figure 8. Schematic diagrams of charge separation and transfer process on BiOI/TiO2 heterostructures and proposed mechanism for photocatalytic selective hydroxylation of phenol with BiOI/TiO2 heterostructures [134]. Reprinted with permission from Ref. [138]. Copyright 2024 Elsevier.

Figure 9. Scheme of submerged ceramic membrane reactor for phenol hydroxylation to [154]. Reprinted with permission from Ref. [146]. Copyright 2024 John Wiley and Sons.

Table 2

Representative examples of molecular sieves as the catalysts of phenol hydroxylation.

Catalyst	Temperature (°C); Reaction Time, h	Conversion (wt. %)	Si/Ti mol. Ratio	HQ/CAT Ratio	Reference
TS-1	57; 6	93	10	0.88	[67]
TS-1		90	17	0.85
TS-1		87	23	0.89
TS-1		78	47	0.89
TS-1		60	100	0.82
TS-1	30; 4	16.6	50	0.28	[21]
Ti-MCM-41	30; 4	12.7	50	0.03
TS-2	57; 0.5	-	65	0.98	[61]
Ti-BEA	60; 6	19.5	40	0.5	[15]
Ti-UZM-35	70; 1	48.4 *	70	12	[68]
Ti-SBA-12	80; 24	24.1	46	1.1	[55]
Ti-SBA-16	80; 24	13.3	41	0.5
Ti-MTS-9	80; 4	26.3	30	0.67	[69]
Ti-HMS	80; 4	0.5	30	0.71
HTS-1	80; 6	23.5	51.5	2.4	[70]
mesoTS-1	70; 3	17.7	56	1.8	[56]
Ti-MCM-68	100; 0.17	17.1	90	2	[71]
Ti-YNU-2	100; 0.17	74.3	105	9.6

* Yield of CAT + HQ.

References

1. Krumenacker, L.; Costantini, M.; Pontal, P.; Sentenac, J. Hydroquinone, Resorcinol, and Catechol. Kirk-Othmer Encyclopedia of Chemical Technology; Wiley: Hoboken, NJ, USA, 2000.

2. Suresh, S.; Srivastava, V.C.; Mishra, I.M. Adsorption of Catechol, Resorcinol, Hydroquinone, and Their Derivatives: A Review. Int. J. Energy Environ. Eng.; 2012; 3, 32. [DOI: https://dx.doi.org/10.1186/2251-6832-3-32]

3. ChemAnalyst Report. Hydroquinone Market Size, Share, Growth & Forecast; ChemAnalysis: New York, NY, USA, 2023.

4. Market Research Report. Global Dihydroxybenzenes 2019–2030; Market Research: Rockville, MD, USA, 2023.

5. Ran, N.; Knop, D.R.; Draths, K.M.; Frost, J.W. Benzene-Free Synthesis of Hydroquinone. J. Am. Chem. Soc.; 2001; 123, pp. 10927-10934. [DOI: https://dx.doi.org/10.1021/ja016460p] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/11686696]

6. Carleton, P.S. Process for Preparing Hydroquinone and Acetone 1975. U.S. Patent; No. 4,207,265, 10 June 1980.

7. Costantini, M.; Fache, E.; Michelet, D.; Manaut, D. Selective Access to Hydroquinone: «Fuchsone Route. Industrial Chemistry Library; Elsevier: Amsterdam, The Netherlands, 1996; Volume 8, pp. 350-367.

8. Wang, C.; Zhang, J.; Zheng, W.; Ren, Y.; Yue, B.; He, H. Direct Hydroxylation of Benzene to Phenol on Solid-State Catalyst. Industrial Arene Chemistry; Wiley: Hoboken, NJ, USA, 2023; Volume 3, pp. 1385-1410. ISBN 9783527827992

9. Burton, R. Oxidant Concentration Effects in the Hydroxylation of Phenol over Titanium-Based Zeolites Al-Free Ti-Beta and TS-1. Ph.D. Thesis; University of Stellenbosch: Stellenbosch, South Africa, 2006.

10. Centi, G.; Perathoner, S. One-Step H₂O₂ and Phenol Syntheses: Examples of Challenges for New Sustainable Selective Oxidation Processes. Catal. Today; 2009; 143, pp. 145-150. [DOI: https://dx.doi.org/10.1016/j.cattod.2008.09.032]

11. Bokare, A.D.; Choi, W. Review of Iron-Free Fenton-like Systems for Activating H₂O₂ in Advanced Oxidation Processes. J. Hazard. Mater.; 2014; 275, pp. 121-135. [DOI: https://dx.doi.org/10.1016/j.jhazmat.2014.04.054] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/24857896]

12. Lewis, R.J.; Hutchings, G.J. Recent Advances in the Direct Synthesis of H₂O₂. ChemCatChem; 2019; 11, pp. 298-308. [DOI: https://dx.doi.org/10.1002/cctc.201801435]

13. Mizuno, N.; Kamata, K. Catalytic Oxidation of Hydrocarbons with Hydrogen Peroxide by Vanadium-Based Polyoxometalates. Coord. Chem. Rev.; 2011; 255, pp. 2358-2370. [DOI: https://dx.doi.org/10.1016/j.ccr.2011.01.041]

14. Tkachenko, N.V.; Ottenbacher, R.V.; Lyakin, O.Y.; Zima, A.M.; Samsonenko, D.G.; Talsi, E.P.; Bryliakov, K.P. Highly Efficient Aromatic C−H Oxidation with H₂O₂ in the Presence of Iron Complexes of the PDP Family. ChemCatChem; 2018; 10, pp. 4052-4057. [DOI: https://dx.doi.org/10.1002/cctc.201800832]

15. Wilkenhöner, U.; van Steen, E.; Langhendries, G.; Baron, G.V.; van Laar, F.; Jacobs, P.A.; Gammon, D.W. Influence of Pore and Crystal Size of Crystalline Titanosilicates on Phenol Hydroxylation in Different Solvents. J. Catal.; 2001; 203, pp. 201-212. [DOI: https://dx.doi.org/10.1006/jcat.2001.3308]

16. Naik, B.; Parida, K.M.; Behera, G.C. Facile Synthesis of Bi₂O₃/TiO₂-XNx and Its Direct Solar-Light-Driven Photocatalytic Selective Hydroxylation of Phenol. ChemCatChem; 2011; 3, pp. 311-318. [DOI: https://dx.doi.org/10.1002/cctc.201000233]

17. Yusuf, S.; Dinari, M.; Moheb, A. Facial Synthesis of V-Containing CuMgAl-LDHs as a New Catalyst for the Phenol Hydroxylation. Chem. Phys.; 2021; 546, 111183. [DOI: https://dx.doi.org/10.1016/j.chemphys.2021.111183]

18. Callanan, L.H.; Burton, R.M.; Wilkenhóner, U.; Van, S. Phenol Hydroxylation of over Aluminium-Free Titanium-Beta Using Water as a Solvent. Studies in Surface Science and Catalysis; Elsevier: Amsterdam, The Netherlands, 2004; Volume 154 C, pp. 2596-2602.

19. Rives, V.; Prieto, O.; Dubey, A.; Kannan, S. Synergistic Effect in the Hydroxylation of Phenol over CoNiAl Ternary Hydrotalcites. J. Catal.; 2003; 220, pp. 161-171. [DOI: https://dx.doi.org/10.1016/S0021-9517(03)00245-8]

20. Hai, L.; Zhang, T.; Zhang, X.; Zhang, G.; Li, B.; Jiang, S.; Ma, X. Catalytic Hydroxylation of Phenol to Dihydroxybenzene by Fe(II) Complex in Aqueous Phase at Ambient Temperature. Catal. Commun.; 2017; 101, pp. 93-97. [DOI: https://dx.doi.org/10.1016/j.catcom.2017.08.001]

21. Lee, G.D.; Kim, S.G.; Jeong, H.H.; Park, S.S.; Hong, S.S. Photocatalytic Hydroxylation of Phenol over Ti-Containing Zeolites (TS-1, Ti-MCM-41). Solid State Phenom.; 2007; 124–126, pp. 1793-1796. [DOI: https://dx.doi.org/10.4028/www.scientific.net/SSP.124-126.1793]

22. Parmon, V.N.; Panov, G.I.; Uriarte, A.; Noskov, A.S. Nitrous Oxide in Oxidation Chemistry and Catalysis: Application and Production. Catal. Today; 2005; 100, pp. 115-131. [DOI: https://dx.doi.org/10.1016/j.cattod.2004.12.012]

23. Zuo, Y.; Liu, M.; Ma, M.; Song, C.; Guo, X. Improved Catalytic Performance for 1-Butene Epoxidation over Titanium Silicalite-1 Extrudates by Using SBA-15 or Carborundum as Additives. Ind. Eng. Chem. Res.; 2017; 56, pp. 7462-7467. [DOI: https://dx.doi.org/10.1021/acs.iecr.7b01482]

24. Notari, B. Synthesis and Catalytic Properties of Titanium Containing Zeolites. Proceedings of the Studies in Surface Science and Catalysis; Elsevier: Amsterdam, The Netherlands, 1988; Volume 37, pp. 413-425.

25. Zuo, Y.; Song, W.; Dai, C.; He, Y.; Wang, M.; Wang, X.; Guo, X. Modification of Small-Crystal Titanium Silicalite-1 with Organic Bases: Recrystallization and Catalytic Properties in the Hydroxylation of Phenol. Appl. Catal. A Gen.; 2013; 453, pp. 272-279. [DOI: https://dx.doi.org/10.1016/j.apcata.2012.12.027]

26. Han, Z.; Zhang, F.; Zhao, X. Green Energy-Efficient Synthesis of Fe-ZSM-5 Zeolite and Its Application for Hydroxylation of Phenol. Microporous Mesoporous Mater.; 2019; 290, 109679. [DOI: https://dx.doi.org/10.1016/j.micromeso.2019.109679]

27. Salazar-Aguilar, A.D.; Vega, G.; Casas, J.A.; Vega-Díaz, S.M.; Tristan, F.; Meneses-Rodríguez, D.; Belmonte, M.; Quintanilla, A. Direct Hydroxylation of Phenol to Dihydroxybenzenes by H₂O₂ and Fe-Based Metal-Organic Framework Catalyst at Room Temperature. Catalysts; 2020; 10, 172. [DOI: https://dx.doi.org/10.3390/catal10020172]

28. Perego, C.; de Angelis, A.; Pollesel, P.; Millini, R. Zeolite-Based Catalysis for Phenol Production. Ind. Eng. Chem. Res.; 2021; 60, pp. 6379-6402. [DOI: https://dx.doi.org/10.1021/acs.iecr.0c05886]

29. Weber, M.; Weber, M. Phenols. Phenolic Resins: A Century of Progress; Springer: Berlin/Heidelberg, Germany, 2010; pp. 9-23. ISBN 9783642047138

30. Kholdeeva, O.A.; Zalomaeva, O.V. Recent Advances in Transition-Metal-Catalyzed Selective Oxidation of Substituted Phenols and Methoxyarenes with Environmentally Benign Oxidants. Coord. Chem. Rev.; 2016; 306, pp. 302-330. [DOI: https://dx.doi.org/10.1016/j.ccr.2015.07.019]

31. Jiang, T.; Wang, W.; Han, B. Catalytic Hydroxylation of Benzene to Phenol with Hydrogen Peroxide Using Catalysts Based on Molecular Sieves. New J. Chem.; 2013; 37, pp. 1654-1664. [DOI: https://dx.doi.org/10.1039/c3nj41163j]

32. Fairuzov, D.; Gerzeliev, I.; Maximov, A.; Naranov, E. Catalytic Dehydrogenation of Ethane: A Mini Review of Recent Advances and Perspective of Chemical Looping Technology. Catalysts; 2021; 11, 833. [DOI: https://dx.doi.org/10.3390/catal11070833]

33. Naranov, E.R.; Dement’ev, K.I.; Gerzeliev, I.M.; Kolesnichenko, N.V.; Roldugina, E.A.; Maksimov, A.L. The Role of Zeolite Catalysis in Modern Petroleum Refining: Contribution from Domestic Technologies. Pet. Chem.; 2019; 59, pp. 247-261. [DOI: https://dx.doi.org/10.1134/S0965544119030101]

34. Naranov, E.R.; Sadovnikov, A.A.; Arapova, O.V.; Bugaev, A.L.; Usoltsev, O.A.; Gorbunov, D.N.; Russo, V.; Murzin, D.Y.; Maximov, A.L. Mechanistic Insights on Ru Nanoparticle In Situ Formation during Hydrodeoxygenation of Lignin-Derived Substances to Hydrocarbons. Catal. Sci. Technol.; 2023; 13, pp. 1571-1583. [DOI: https://dx.doi.org/10.1039/D2CY01127A]

35. Naranov, E.R.; Maximov, A.L. Selective Conversion of Aromatics into Cis-Isomers of Naphthenes Using Ru Catalysts Based on the Supports of Different Nature. Catal. Today; 2019; 329, pp. 94-101. [DOI: https://dx.doi.org/10.1016/j.cattod.2018.10.068]

36. Tanarungsun, G.; Kiatkittipong, W.; Praserthdam, P.; Yamada, H.; Tagawa, T.; Assabumrungrat, S. Hydroxylation of Benzene to Phenol on Fe/TiO₂ Catalysts Loaded with Different Types of Second Metal. Catal. Commun.; 2008; 9, pp. 1886-1890. [DOI: https://dx.doi.org/10.1016/j.catcom.2008.03.008]

37. Rao, P.R.H.P.; Ramaswamy, A.V. Catalytic Hydroxylation of Phenol over a Vanadium Silicate Molecular Sieve with MEL Structure. Appl. Catal. A Gen.; 1993; 93, pp. 123-130. [DOI: https://dx.doi.org/10.1016/0926-860X(93)85188-U]

38. Xu, D.; Jia, L.; Guo, X. Cu-Doped Mesoporous VOx-TiO₂ in Catalytic Hydroxylation of Benzene to Phenol. Cuihua Xuebao Chinese J. Catal.; 2013; 34, pp. 341-350. [DOI: https://dx.doi.org/10.1016/S1872-2067(11)60487-7]

39. He, J.; Xu, W.; Evans, D.G.; Duan, X.; Li, C. yue Role of Pore Size and Surface Properties of Ti-MCM-41 Catalysts in the Hydroxylation of Aromatics in the Liquid Phase. Microporous Mesoporous Mater.; 2001; 44–45, pp. 581-586. [DOI: https://dx.doi.org/10.1016/S1387-1811(01)00237-2]

40. Barbera, D.; Cavani, F.; D’Alessandro, T.; Fornasari, G.; Guidetti, S.; Aloise, A.; Giordano, G.; Piumetti, M.; Bonelli, B.; Zanzottera, C. The Control of Selectivity in Benzene Hydroxylation Catalyzed by TS-1: The Solvent Effect and the Role of Crystallite Size. J. Catal.; 2010; 275, pp. 158-169. [DOI: https://dx.doi.org/10.1016/j.jcat.2010.07.030]

41. Bhaumik, A.; Mukherjee, P.; Kumar, R. Triphase Catalysis over Titanium-Silicate Molecular Sieves under Solvent-Free Conditions: I. Direct Hydroxylation of Benzene. J. Catal.; 1998; 178, pp. 101-107. [DOI: https://dx.doi.org/10.1006/jcat.1998.2131]

42. Jing, H.; Guo, Z.; Ma, H.; Evans, D.G.; Duan, X. Enhancing the Selectivity of Benzene Hydroxylation by Tailoring the Chemical Affinity of the MCM-41 Catalyst Surface for the Reactive Molecules. J. Catal.; 2002; 212, pp. 22-32. [DOI: https://dx.doi.org/10.1006/jcat.2002.3779]

43. Balducci, L.; Bianchi, D.; Bortolo, R.; D’Aloisio, R.; Ricci, M.; Tassinari, R.; Ungarelli, R. Direct Oxidation of Benzene to Phenol with Hydrogen Peroxide over a Modified Titanium Silicalite. Angew. Chemie; 2003; 115, pp. 5087-5090. [DOI: https://dx.doi.org/10.1002/ange.200352184]

44. Lin, K.; Wang, L.; Meng, F.; Sun, Z.; Yang, Q.; Cui, Y.; Jiang, D.; Xiao, F.S. Formation of Better Catalytically Active Titanium Species in Ti-MCM-41 by Vapor-Phase Silylation. J. Catal.; 2005; 235, pp. 423-427. [DOI: https://dx.doi.org/10.1016/j.jcat.2005.08.003]

45. Kong, A.G.; Wang, H.W.; Yang, X.; Hou, Y.W.; Shan, Y.K. A Facile Direct Route to Synthesize Large-Pore Mesoporous Silica Incorporating High CuO Loading with Special Catalytic Property. Microporous Mesoporous Mater.; 2009; 118, pp. 348-353. [DOI: https://dx.doi.org/10.1016/j.micromeso.2008.09.006]

46. Abbo, H.S.; Titinchi, S.J.J. Transition Metal Coordination Polymers: Synthesis and Catalytic Study for Hydroxylation of Phenol and Benzene. Appl. Catal. A Gen.; 2012; 435–436, pp. 148-155. [DOI: https://dx.doi.org/10.1016/j.apcata.2012.05.048]

47. Parida, K.M.; Rath, D. Structural Properties and Catalytic Oxidation of Benzene to Phenol over CuO-Impregnated Mesoporous Silica. Appl. Catal. A Gen.; 2007; 321, pp. 101-108. [DOI: https://dx.doi.org/10.1016/j.apcata.2007.01.054]

48. Parvulescul, V.; Constantin, C.; Su, B.L. Liquid Phase Oxidation of Aromatic Hydrocarbons Using Highly Ordered Nb and NbCo-MCM-41 Nanoreactors. J. Mol. Catal. A Chem.; 2003; 202, pp. 171-178. [DOI: https://dx.doi.org/10.1016/S1381-1169(03)00202-4]

49. Monfared, H.H.; Amouei, Z. Hydrogen Peroxide Oxidation of Aromatic Hydrocarbons by Immobilized Iron(III). J. Mol. Catal. A Chem.; 2004; 217, pp. 161-164. [DOI: https://dx.doi.org/10.1016/j.molcata.2004.03.020]

50. Liu, T.; Wei, X.; Zhao, J.; Xie, H.; Wang, T.; Zong, Z. Microwave-Assisted Hydroxylation of Benzene to Phenol with H₂O₂ over FeSO₄/SiO₂. Min. Sci. Technol.; 2010; 20, pp. 93-96. [DOI: https://dx.doi.org/10.1016/S1674-5264(09)60167-8]

51. Choi, J.S.; Kim, T.H.; Choo, K.Y.; Sung, J.S.; Saidutta, M.B.; Ryu, S.O.; Song, S.D.; Ramachandra, B.; Rhee, Y.W. Direct Synthesis of Phenol from Benzene on Iron-Impregnated Activated Carbon Catalysts. Appl. Catal. A Gen.; 2005; 290, pp. 1-8. [DOI: https://dx.doi.org/10.1016/j.apcata.2005.04.060]

52. Renuka, N.K. A Green Approach for Phenol Synthesis over Fe3+/MgO Catalysts Using Hydrogen Peroxide. J. Mol. Catal. A Chem.; 2010; 316, pp. 126-130. [DOI: https://dx.doi.org/10.1016/j.molcata.2009.10.010]

53. Tanarungsun, G.; Kiatkittipong, W.; Assabumrungrat, S.; Yamada, H.; Tagawa, T.; Praserthdam, P. Liquid Phase Hydroxylation of Benzene to Phenol with Hydrogen Peroxide Catalyzed by Fe(III)/TiO₂ Catalysts at Room Temperature. J. Ind. Eng. Chem.; 2007; 13, pp. 444-451.

54. Tanarungsun, G.; Kiatkittipong, W.; Praserthdam, P.; Yamada, H.; Tagawa, T.; Assabumrungrat, S. Ternary Metal Oxide Catalysts for Selective Oxidation of Benzene to Phenol. J. Ind. Eng. Chem.; 2008; 14, pp. 596-601. [DOI: https://dx.doi.org/10.1016/j.jiec.2008.04.005]

55. Kumar, A.; Srinivas, D. Hydroxylation of Phenol with Hydrogen Peroxide Catalyzed by Ti-SBA-12 and Ti-SBA-16. J. Mol. Catal. A Chem.; 2013; 368–369, pp. 112-118. [DOI: https://dx.doi.org/10.1016/j.molcata.2012.11.026]

56. Huang, D.-G.; Hu, S.-L.; Chao, Z.-S.; Wu, D.; Ruan, H. Preparation of Open and Hierarchical Porous TS-1 and Its Catalytic Performance in Phenol Hydroxylation. J. Porous Mater.; 2024; 31, pp. 1697-1710. [DOI: https://dx.doi.org/10.1007/s10934-024-01623-7]

57. Song, S.; Zhao, W.; Wang, L.; Chu, J.; Qu, J.; Li, S.; Wang, L.; Qi, T. One-Step Synthesis of Ti-MSU and Its Catalytic Performance on Phenol Hydroxylation. J. Colloid Interface Sci.; 2011; 354, pp. 686-690. [DOI: https://dx.doi.org/10.1016/j.jcis.2010.11.025] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/21145559]

58. Wróblewska, A.; Wójtowicz, G.; Makuch, E. Hydroxylation of Phenol with Hydrogen Peroxide over the Ti-MWW Catalyst in the Presence of Acetonitrile. J. Adv. Oxid. Technol.; 2011; 14, pp. 267-275. [DOI: https://dx.doi.org/10.1515/jaots-2011-0212]

59. Klaewkla, R.; Rirksomboon, T.; Kulprathipanja, S.; Nemeth, L.; Rangsunvigit, P. Light Sensitivity of Phenol Hydroxylation with TS-1. Catal. Commun.; 2006; 7, pp. 260-263. [DOI: https://dx.doi.org/10.1016/j.catcom.2005.10.015]

60. Kim, J.H.; Do, Y.J.; Park, J.H.; Park, S.S.; Hong, S.S.; Lee, G.D. Comparative Study of Photo- and Thermal Catalytic Hydroxylation of Phenol with H 2 O 2 over TS-1. React. Kinet. Catal. Lett.; 2004; 83, pp. 377-383. [DOI: https://dx.doi.org/10.1023/B:REAC.0000046100.51547.77]

61. Reddy, J.S.; Kumar, R.; Ratnasamy, P. Titanium Silicalite-2: Synthesis, Characterization and Catalytic Properties. Appl. Catal.; 1990; 58, pp. L1-L4. [DOI: https://dx.doi.org/10.1016/S0166-9834(00)82273-3]

62. Tyablikov, I.A.; Romanovsky, B.V. Mass Transfer Effect on the Oxidation of Alkenes and Phenol with Hydrogen Peroxide Using TS-1 Titanosilicate as a Catalyst. Catal. Letters; 2017; 147, pp. 2434-2439. [DOI: https://dx.doi.org/10.1007/s10562-017-2136-z]

63. Carati, A.; Flego, C.; Previde Massara, E.; Millini, R.; Carluccio, L.; Parker, W.; Bellussi, G. Stability of Ti in MFI and Beta Structures: A Comparative Study. Microporous Mesoporous Mater.; 1999; 30, pp. 137-144. [DOI: https://dx.doi.org/10.1016/S1387-1811(99)00018-9]

64. Datta, R.; Leung, S.W.K. Shape Generalized Isothermal Effectiveness Factor for First-Order Kinetics. Chem. Eng. Commun.; 1985; 39, pp. 155-173. [DOI: https://dx.doi.org/10.1080/00986448508911668]

65. Tyablikov, I. Synthesis and Physicochemical Properties of Titanosilicate with MFI Structure as a Catalyst for Epoxidation of Alkenes; Moscow State University: Moscow, Russia, 2019.

66. Kim, J.; Chun, J.; Ryoo, R. MFI Zeolite Nanosheets with Post-Synthetic Ti Grafting for Catalytic Epoxidation of Bulky Olefins Using H₂O₂. Chem. Commun.; 2015; 51, pp. 13102-13105. [DOI: https://dx.doi.org/10.1039/C5CC04510J]

67. Thangaraj, A.; Kumar, R.; Ratnasamy, P. Catalytic Properties of Crystalline Titanium Silicalites II. Hydroxylation of Phenol with Hydrogen Peroxide over TS-1 Zeolites. J. Catal.; 1991; 131, pp. 294-297. [DOI: https://dx.doi.org/10.1016/0021-9517(91)90347-7]

68. Yin, J.; Lu, X.; Yan, J.; Su, F.; Streiff, S.; Xu, H.; Wu, P. Postsynthesis of Ti-UZM-35 Titanosilicate as Efficient Catalyst for Phenol Hydroxylation Reaction. Microporous Mesoporous Mater.; 2020; 305, 110321. [DOI: https://dx.doi.org/10.1016/j.micromeso.2020.110321]

69. Meng, X.; Li, D.; Yang, X.; Yu, Y.; Wu, S.; Han, Y.; Yang, Q.; Jiang, D.; Xiao, F.-S. Synthesis, Characterization, and Catalytic Activity of Mesostructured Titanosilicates Assembled from Polymer Surfactants with Preformed Titanosilicate Precursors in Strongly Acidic Media. J. Phys. Chem. B; 2003; 107, pp. 8972-8980. [DOI: https://dx.doi.org/10.1021/jp027405l]

70. Han, Z.; Shen, Y.; Wang, F.; Zhang, X. Synthesis of Hierarchical Titanium Silicalite-1 in the Presence of Polyquaternium-7 and Its Application in the Hydroxylation of Phenol. J. Mater. Sci.; 2018; 53, pp. 12837-12849. [DOI: https://dx.doi.org/10.1007/s10853-018-2582-z]

71. Sasaki, M.; Sato, Y.; Tsuboi, Y.; Inagaki, S.; Kubota, Y. Ti-YNU-2: A Microporous Titanosilicate with Enhanced Catalytic Performance for Phenol Oxidation. ACS Catal.; 2014; 4, pp. 2653-2657. [DOI: https://dx.doi.org/10.1021/cs5007926]

72. Yue, Y.; Gédéon, A.; Bonardet, J.L.; Melosh, N.; D’Espinose, J.B.; Fraissard, J. Direct Synthesis of AlSBA Mesoporous Molecular Sieves: Characterization and Catalytic Activities. Chem. Commun.; 1999; pp. 1967-1968. [DOI: https://dx.doi.org/10.1039/a904467a]

73. Schmidt, R.; Stöcker, M.; Hansen, E.; Akporiaye, D.; Ellestad, O.H. MCM-41: A Model System for Adsorption Studies on Mesoporous Materials. Microporous Mater.; 1995; 3, pp. 443-448. [DOI: https://dx.doi.org/10.1016/0927-6513(94)00055-Z]

74. Alam, S.; Selatan, S.P.; Pinang, P. A Review: Mesoporous Santa Barbara Amorphous-15, Types, Synthesis and Its Applications towards Biorefinery Production. Am. J. Appl. Sci.; 2010; 7, pp. 1579-1586.

75. Herney-Ramirez, J.; Vicente, M.A.; Madeira, L.M. Heterogeneous Photo-Fenton Oxidation with Pillared Clay-Based Catalysts for Wastewater Treatment: A Review. Appl. Catal. B Environ.; 2010; 98, pp. 10-26. [DOI: https://dx.doi.org/10.1016/j.apcatb.2010.05.004]

76. Liotta, L.F.; Gruttadauria, M.; Di Carlo, G.; Perrini, G.; Librando, V. Heterogeneous Catalytic Degradation of Phenolic Substrates: Catalysts Activity. J. Hazard. Mater.; 2009; 162, pp. 588-606. [DOI: https://dx.doi.org/10.1016/j.jhazmat.2008.05.115] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/18586389]

77. Rokhina, E.V.; Virkutyte, J. Environmental Application of Catalytic Processes: Heterogeneous Liquid Phase Oxidation of Phenol with Hydrogen Peroxide. Crit. Rev. Environ. Sci. Technol.; 2011; 41, pp. 125-167. [DOI: https://dx.doi.org/10.1080/10643380802669018]

78. Silvestre-Albero, A.; Grau-Atienza, A.; Serrano, E.; García-Martínez, J.; Silvestre-Albero, J. Desilication of TS-1 Zeolite for the Oxidation of Bulky Molecules. Catal. Commun.; 2014; 44, pp. 35-39. [DOI: https://dx.doi.org/10.1016/j.catcom.2013.08.004]

79. Shakeri, M.; Dehghanpour, S.B. Rational Synthesis of TS-1 Zeolite to Direct Both Particle Size and Framework Ti in Favor of Enhanced Catalytic Performance. Microporous Mesoporous Mater.; 2020; 298, 110066. [DOI: https://dx.doi.org/10.1016/j.micromeso.2020.110066]

80. Xiong, G.; Cao, Y.; Guo, Z.; Jia, Q.; Tian, F.; Liu, L. The Roles of Different Titanium Species in TS-1 Zeolite in Propylene Epoxidation Studied by in Situ UV Raman Spectroscopy. Phys. Chem. Chem. Phys.; 2016; 18, pp. 190-196. [DOI: https://dx.doi.org/10.1039/C5CP05268H]

81. Huybrechts, D.R.C.; Vaesen, I.; Li, H.X.; Jacobs, P.A. Factors Influencing the Catalytic Activity of Titanium Silicalites in Selective Oxidations. Catal. Lett.; 1991; 8, pp. 237-244. [DOI: https://dx.doi.org/10.1007/BF00764122]

82. Zhang, N.; Shi, L.; Yu, T.; Li, T.; Hua, W.; Lin, C. Synthesis and Characterization of Pure STW-Zeotype Germanosilicate, Cu- and Co-Substituted STW-Zeotype Materials. J. Solid State Chem.; 2015; 225, pp. 271-277. [DOI: https://dx.doi.org/10.1016/j.jssc.2014.12.031]

83. Přech, J. Catalytic Performance of Advanced Titanosilicate Selective Oxidation Catalysts—A Review. Catal. Rev.; 2018; 60, pp. 71-131. [DOI: https://dx.doi.org/10.1080/01614940.2017.1389111]

84. Mal, N.K.; Ramaswamy, A.V. Hydroxylation of Phenol over Sn-Silicalite-1 Molecular Sieve: Solvent Effects. J. Mol. Catal. A Chem.; 1996; 105, pp. 149-158. [DOI: https://dx.doi.org/10.1016/1381-1169(95)00204-9]

85. Ramaswamy, V.; Tripathi, B.; Srinivas, D.; Ramaswamy, A.V.; Cattaneo, R.; Prins, R. Structure and Redox Behavior of Zirconium in Microporous Zr-Silicalites Studied by EXAFS and ESR Techniques. J. Catal.; 2001; 200, pp. 250-258. [DOI: https://dx.doi.org/10.1006/jcat.2001.3213]

86. Chen, J.; Eberlein, L.; Langford, C.H. Pathways of Phenol and Benzene Photooxidation Using TiO₂ Supported on a Zeolite. J. Photochem. Photobiol. A Chem.; 2002; 148, pp. 183-189. [DOI: https://dx.doi.org/10.1016/S1010-6030(02)00041-2]

87. Letaïef, S.; Casal, B.; Aranda, P.; Martín-Luengo, M.A.; Ruiz-Hitzky, E. Fe-Containing Pillared Clays as Catalysts for Phenol Hydroxylation. Appl. Clay Sci.; 2003; 22, pp. 263-277. [DOI: https://dx.doi.org/10.1016/S0169-1317(03)00079-6]

88. Del Castillo, H.L.; Gil, A.; Grange, P. Hydroxylation of Phenol on Titanium Pillared Montmorillonite. Clays Clay Miner.; 1996; 44, pp. 706-709. [DOI: https://dx.doi.org/10.1346/CCMN.1996.0440514]

89. He, J.; Jiang, Y.; Ding, B.; Wang, Y.; Qiu, H.; Dai, S.; Zhao, X.; Hou, Z. Zirconium Phosphate Supported Copper Catalyst for Selective Oxidation of Phenol to Cis, Cis-Muconic Acid. Appl. Catal. A Gen.; 2023; 664, 119351. [DOI: https://dx.doi.org/10.1016/j.apcata.2023.119351]

90. Sheldon, R.A.; Dakka, J. Heterogeneous Catalytic Oxidations in the Manufacture of Fine Chemicals. Catal. Today; 1994; 19, pp. 215-245. [DOI: https://dx.doi.org/10.1016/0920-5861(94)80186-X]

91. Shen, Y.; Wang, F.; Liu, W.; Zhang, X. The Preparation of Fe³⁺ Ion-Exchanged Mesopore Containing ZSM-5 Molecular Sieves and Its High Catalytic Activity in the Hydroxylation of Phenol. J. Porous Mater.; 2018; 25, pp. 1587-1595. [DOI: https://dx.doi.org/10.1007/s10934-018-0572-9]

92. Karakhanov, E.A.; Maximov, A.L.; Kardasheva, Y.S.; Skorkin, V.A.; Kardashev, S.V.; Predeina, V.V.; Talanova, M.Y.; Lurie-Luke, E.; Seeley, J.A.; Cron, S.L. Copper Nanoparticles as Active Catalysts in Hydroxylation of Phenol by Hydrogen Peroxide. Appl. Catal. A Gen.; 2010; 385, pp. 62-72. [DOI: https://dx.doi.org/10.1016/j.apcata.2010.06.042]

93. Xia, C.; Long, L.; Zhu, B.; Lin, M.; Shu, X. Enhancing the Selectivity of Pare-Dihydroxybenzene in Hollow Titanium Silicalite Zeolite Catalyzed Phenol Hydroxylation by Introducing Acid-Base Sites. Catal. Commun.; 2016; 80, pp. 49-52. [DOI: https://dx.doi.org/10.1016/j.catcom.2016.03.011]

94. Romanelli, G.; Villabrille, P.; Vazquez, P.; Caceres, C.; Tundo, P. Phenol and Naphthol Oxidation to Quinones with Hydrogen Peroxide Using Vanadium-Substituted Keggin Heteropoly Acid as Catalyst. Lett. Org. Chem.; 2008; 5, pp. 332-335. [DOI: https://dx.doi.org/10.2174/157017808784872142]

95. Vijayan, P.; Anitha, P.; Rajeshkumar, M.; Viswanathamurthi, P.; Sugumar, P.; Ponnuswamy, M.N. Enhanced Catalytic Activity towards One-Pot Hydroxylation of Phenol with Hydrogen Peroxide by Nickel(II) Complex Encompassing 3-Formylchromone-S-Methylisothiosemicarbazone Derivatives. Polyhedron; 2017; 124, pp. 77-85. [DOI: https://dx.doi.org/10.1016/j.poly.2016.12.031]

96. Li, S.; Li, G.; Wu, G.; Hu, C.; Lee, G. Microporous Carbon Molecular Sieve as a Novel Catalyst for the Hydroxylation of Phenol. Microporous Mesoporous Mater.; 2011; 143, pp. 22-29. [DOI: https://dx.doi.org/10.1016/j.micromeso.2011.02.001]

97. Zhang, Q.; Guo, Q.; Wang, X.; Shishido, T.; Wang, Y. Iron-Catalyzed Propylene Epoxidation by Nitrous Oxide: Toward Understanding the Nature of Active Iron Sites with Modified Fe-MFI and Fe-MCM-41 Catalysts. J. Catal.; 2006; 239, pp. 105-116. [DOI: https://dx.doi.org/10.1016/j.jcat.2006.01.023]

98. Lou, L.L.; Liu, S. CuO-Containing MCM-48 as Catalysts for Phenol Hydroxylation. Catal. Commun.; 2005; 6, pp. 762-765. [DOI: https://dx.doi.org/10.1016/j.catcom.2005.07.004]

99. Wu, Q.; Hu, X.; Yue, P.L.; Zhao, X.S.; Lu, G.Q. Copper/MCM-41 as Catalyst for the Wet Oxidation of Phenol. Appl. Catal. B Environ.; 2001; 32, pp. 151-156. [DOI: https://dx.doi.org/10.1016/S0926-3373(01)00131-X]

100. Takeguchi, T.; Kim, J.B.; Kang, M.; Inui, T.; Cheuh, W.T.; Haller, G.L. Synthesis and Characterization of Alkali-Free, Ga-Substituted MCM-41 and Its Performance for n-Hexane Conversion. J. Catal.; 1998; 175, pp. 1-6. [DOI: https://dx.doi.org/10.1006/jcat.1998.1973]

101. Sobczak, I.; Ziolek, M.; Renn, M.; Decyk, P.; Nowak, I.; Daturi, M.; Lavalley, J.C. Cu State and Behaviour in MCM-41 Mesoporous Molecular Sieves Modified with Copper during the Synthesis—Comparison with Copper Exchanged Materials. Microporous Mesoporous Mater.; 2004; 74, pp. 23-36. [DOI: https://dx.doi.org/10.1016/j.micromeso.2004.05.015]

102. Dai, P.S.E.; Petty, R.H.; Ingram, C.W.; Szostak, R. Metal Substituted Aluminophosphate Molecular Sieves as Phenol Hydroxylation Catalysts. Appl. Catal. A Gen.; 1996; 143, pp. 101-110. [DOI: https://dx.doi.org/10.1016/0926-860X(96)00073-7]

103. Noreña-Franco, L.; Hernandez-Perez, I.; Aguilar-Pliego, J.; Maubert-Franco, A. Selective Hydroxylation of Phenol Employing Cu-MCM-41 Catalysts. Catal. Today; 2002; 75, pp. 189-195. [DOI: https://dx.doi.org/10.1016/S0920-5861(02)00067-6]

104. Zhang, G.; Long, J.; Wang, X.; Zhang, Z.; Dai, W.; Liu, P.; Li, Z.; Wu, L.; Fu, X. Catalytic Role of Cu Sites of Cu/MCM-41 in Phenol Hydroxylation. Langmuir; 2010; 26, pp. 1362-1371. [DOI: https://dx.doi.org/10.1021/la902436s]

105. Jiang, Y.; Lin, K.; Zhang, Y.; Liu, J.; Li, G.; Sun, J.; Xu, X. Fe-MCM-41 Nanoparticles as Versatile Catalysts for Phenol Hydroxylation and for Friedel-Crafts Alkylation. Appl. Catal. A Gen.; 2012; 445–446, pp. 172-179. [DOI: https://dx.doi.org/10.1016/j.apcata.2012.08.016]

106. Wu, C.; Kong, Y.; Gao, F.; Wu, Y.; Lu, Y.; Wang, J.; Dong, L. Synthesis, Characterization and Catalytic Performance for Phenol Hydroxylation of Fe-MCM41 with High Iron Content. Microporous Mesoporous Mater.; 2008; 113, pp. 163-170. [DOI: https://dx.doi.org/10.1016/j.micromeso.2007.11.013]

107. Wang, L.; Kong, A.; Chen, B.; Ding, H.; Shan, Y.; He, M. Direct Synthesis, Characterization of Cu-SBA-15 and Its High Catalytic Activity in Hydroxylation of Phenol by H₂O₂. J. Mol. Catal. A Chem.; 2005; 230, pp. 143-150. [DOI: https://dx.doi.org/10.1016/j.molcata.2004.12.027]

108. Baila, J.; Kiss, T.; Jameson, R.F. Copper(II)-Catalyzed Oxidation of Catechol by Molecular Oxygen in Aqueous Solution. Inorg. Chem.; 1992; 31, pp. 58-62. [DOI: https://dx.doi.org/10.1021/ic00027a012]

109. Arntz, D. Trends in the Chemical Industry. Catal. Today; 1993; 18, pp. 173-198. [DOI: https://dx.doi.org/10.1016/0920-5861(93)85030-4]

110. Centi, G.; Cavani, F.; Trifirò, F. Selective Oxidation by Heterogeneous Catalysis; Fundamental and Applied Catalysis Springer: Boston, MA, USA, 2001; ISBN 978-1-4613-6872-4

111. Shilpa, E.R.; Gayathri, V. Encapsulation of Cu(II)[2-(2′-Hydroxyphenyl)Benzimidazole]2 within Zeolite Nano-Cavity: Structural Properties and Its Catalytic Activity towards Phenol and Styrene Oxidation. J. Environ. Chem. Eng.; 2016; 4, pp. 4194-4206. [DOI: https://dx.doi.org/10.1016/j.jece.2016.09.022]

112. Kubacka, A.; Wang, Z.; Sulikowski, B.; Cortés Corberán, V. Hydroxylation/Oxidation of Benzene over Cu-ZSM-5 Systems: Optimization of the One-Step Route to Phenol. J. Catal.; 2007; 250, pp. 184-189. [DOI: https://dx.doi.org/10.1016/j.jcat.2007.05.017]

113. Taran, O.P.; Yashnik, S.A.; Ayusheev, A.B.; Piskun, A.S.; Prihod’ko, R.V.; Ismagilov, Z.R.; Goncharuk, V.V.; Parmon, V.N. Cu-Containing MFI Zeolites as Catalysts for Wet Peroxide Oxidation of Formic Acid as Model Organic Contaminant. Appl. Catal. B Environ.; 2013; 140–141, pp. 506-515. [DOI: https://dx.doi.org/10.1016/j.apcatb.2013.04.050]

114. Fu, Z.; Chen, J.; Yin, D.; Yin, D.; Zhang, L.; Zhang, Y. Highly Effective Cu-HMS Catalyst for Hydroxylation of Phenol. Catal. Lett.; 2000; 66, pp. 105-108. [DOI: https://dx.doi.org/10.1023/A:1019018816599]

115. Karakhanov, E.A.; Maximov, A.L.; Kardasheva, Y.S.; Skorkin, V.A.; Kardashev, S.V.; Ivanova, E.A.; Lurie-Luke, E.; Seeley, J.A.; Cron, S.L. Hydroxylation of Phenol by Hydrogen Peroxide Catalyzed by Copper(II) and Iron(III) Complexes: The Structure of the Ligand and the Selectivity of Ortho-Hydroxylation. Ind. Eng. Chem. Res.; 2010; 49, pp. 4607-4613. [DOI: https://dx.doi.org/10.1021/ie902040m]

116. Anjali, K.; Ganesh, V.; Christopher, J.; Sakthivel, A. Copper Based Macromolecular Catalysts for the Hydroxylation of Phenols. J. Organomet. Chem.; 2020; 929, 121579. [DOI: https://dx.doi.org/10.1016/j.jorganchem.2020.121579]

117. Antonyraj, C.A.; Gandhi, M.; Kannan, S. Phenol Hydroxylation over Cu-Containing LDHs and Their Calcined Forms: Profound Cobivalent Metal Influence. Ind. Eng. Chem. Res.; 2010; 49, pp. 6020-6026. [DOI: https://dx.doi.org/10.1021/ie100399j]

118. Chen, C.; Xu, C.; Feng, L.; Suo, J.; Qiu, F. Phenol Hydroxylation Catalyzed by the Rare Earth-Adulterated Copper-Containing Hydrotalcites. Chem. Lett.; 2005; 34, pp. 206-207. [DOI: https://dx.doi.org/10.1246/cl.2005.206]

119. Dubey, A.; Rives, V.; Kannan, S. Catalytic Hydroxylation of Phenol over Ternary Hydrotalcites Containing Cu, Ni and Al. J. Mol. Catal. A Chem.; 2002; 181, pp. 151-160. [DOI: https://dx.doi.org/10.1016/S1381-1169(01)00360-0]

120. Kannan, S.; Dubey, A.; Knozinger, H. Synthesis and Characterization of CuMgAl Ternary Hydrotalcites as Catalysts for the Hydroxylation of Phenol. J. Catal.; 2005; 231, pp. 381-392. [DOI: https://dx.doi.org/10.1016/j.jcat.2005.01.032]

121. Zhang, H.; Zhang, G.; Bi, X.; Chen, X. Facile Assembly of a Hierarchical Core@shell Fe3O 4@CuMgAl-LDH (Layered Double Hydroxide) Magnetic Nanocatalyst for the Hydroxylation of Phenol. J. Mater. Chem. A; 2013; 1, pp. 5934-5942. [DOI: https://dx.doi.org/10.1039/c3ta10349h]

122. Cui, G.; Wang, F.; He, S.; Wei, M. Catalytic Performance of Layered Double Hydroxide Nanosheets toward Phenol Hydroxylation. RSC Adv.; 2016; 6, pp. 105406-105411. [DOI: https://dx.doi.org/10.1039/C6RA18917B]

123. Chen, C.; Xu, C.; Feng, L.; Li, Z.; Suo, J.; Qiu, F.; Yang, Y. Effect of Rare Earth Doping on the Catalytic Activity of Copper-Containing Hydrotalcites in Phenol Hydroxylation. Adv. Synth. Catal.; 2005; 347, pp. 1848-1854. [DOI: https://dx.doi.org/10.1002/adsc.200505004]

124. Sun, J.; Meng, X.; Shi, Y.; Wang, R.; Feng, S.; Jiang, D.; Xu, R.; Xiao, F.S. A Novel Catalyst of Cu-Bi-V-O Complex in Phenol Hydroxylation with Hydrogen Peroxide. J. Catal.; 2000; 193, pp. 199-206. [DOI: https://dx.doi.org/10.1006/jcat.2000.2901]

125. Xiong, L.; Tang, J. Strategies and Challenges on Selectivity of Photocatalytic Oxidation of Organic Substances. Adv. Energy Mater.; 2021; 11, 2003216. [DOI: https://dx.doi.org/10.1002/aenm.202003216]

126. Marin, M.L.; Santos-Juanes, L.; Arques, A.; Amat, A.M.; Miranda, M.A. Organic Photocatalysts for the Oxidation of Pollutants and Model Compounds. Chem. Rev.; 2012; 112, pp. 1710-1750. [DOI: https://dx.doi.org/10.1021/cr2000543] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/22040166]

127. Ide, Y.; Ogino, R.; Sadakane, M.; Sano, T. Effects of Au Loading and CO₂ Addition on Photocatalytic Selective Phenol Oxidation over TiO₂-Supported Au Nanoparticles. ChemCatChem; 2013; 5, pp. 766-773. [DOI: https://dx.doi.org/10.1002/cctc.201200661]

128. Sadovnikov, A.A.; Garshev, A.V.; Eliseev, A.A.; Beltiukov, A.N.; Naranov, E.R.; Li, W.; Sutherland, A.J.; Boytsova, O.V. Nanowhiskers of K₂Ti₆O₁₃ as a Promoter of Photocatalysis in Anatase Mesocrystals. Catal. Today; 2021; 378, pp. 133-139. [DOI: https://dx.doi.org/10.1016/j.cattod.2020.12.039]

129. Sadovnikov, A.A.; Naranov, E.R.; Maksimov, A.L.; Baranchikov, A.E.; Ivanov, V.K. Photocatalytic Activity of Fluorinated Titanium Dioxide in Ozone Decomposition. Russ. J. Appl. Chem.; 2022; 95, pp. 118-125. [DOI: https://dx.doi.org/10.1134/S1070427222010153]

130. Ahmed, S.; Rasul, M.G.; Martens, W.N.; Brown, R.; Hashib, M.A. Advances in Heterogeneous Photocatalytic Degradation of Phenols and Dyes in Wastewater: A Review. Water. Air. Soil Pollut.; 2011; 215, pp. 3-29. [DOI: https://dx.doi.org/10.1007/s11270-010-0456-3]

131. Ahmed, S.; Rasul, M.G.; Martens, W.N.; Brown, R.; Hashib, M.A. Heterogeneous Photocatalytic Degradation of Phenols in Wastewater: A Review on Current Status and Developments. Desalination; 2010; 261, pp. 3-18. [DOI: https://dx.doi.org/10.1016/j.desal.2010.04.062]

132. Silva, C.G.; Faria, J.L. Effect of Key Operational Parameters on the Photocatalytic Oxidation of Phenol by Nanocrystalline Sol-Gel TiO₂ under UV Irradiation. J. Mol. Catal. A Chem.; 2009; 305, pp. 147-154. [DOI: https://dx.doi.org/10.1016/j.molcata.2008.12.015]

133. Ye, H.; Lu, S. Photocatalytic Selective Oxidation of Phenol in Suspensions of Titanium Dioxide with Exposed {0 0 1} Facets. Appl. Surf. Sci.; 2013; 277, pp. 94-99. [DOI: https://dx.doi.org/10.1016/j.apsusc.2013.04.008]

134. Li, B.; Chen, X.; Zhang, T.; Jiang, S.; Zhang, G.; Wu, W.; Ma, X. Photocatalytic Selective Hydroxylation of Phenol to Dihydroxybenzene by BiOI/TiO₂ p-n Heterojunction Photocatalysts for Enhanced Photocatalytic Activity. Appl. Surf. Sci.; 2018; 439, pp. 1047-1056. [DOI: https://dx.doi.org/10.1016/j.apsusc.2017.12.220]

135. Hu, Y.; Li, D.; Zheng, Y.; Chen, W.; He, Y.; Shao, Y.; Fu, X.; Xiao, G. BiVO4/TiO₂ Nanocrystalline Heterostructure: A Wide Spectrum Responsive Photocatalyst towards the Highly Efficient Decomposition of Gaseous Benzene. Appl. Catal. B Environ.; 2011; 104, pp. 30-36. [DOI: https://dx.doi.org/10.1016/j.apcatb.2011.02.031]

136. Zhou, W.; Yin, Z.; Du, Y.; Huang, X.; Zeng, Z.; Fan, Z.; Liu, H.; Wang, J.; Zhang, H. Synthesis of Few-Layer MoS2 Nanosheet-Coated TiO₂ Nanobelt Heterostructures for Enhanced Photocatalytic Activities. Small; 2013; 9, pp. 140-147. [DOI: https://dx.doi.org/10.1002/smll.201201161] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/23034984]

137. Zhao, L.; Cui, T.; Li, Y.; Wang, B.; Han, J.; Han, L.; Liu, Z. Efficient Visible Light Photocatalytic Activity of P-n Junction CuO/TiO₂ Loaded on Natural Zeolite. RSC Adv.; 2015; 5, pp. 64495-64502. [DOI: https://dx.doi.org/10.1039/C5RA07597A]

138. Wang, M.; Hu, Y.; Han, J.; Guo, R.; Xiong, H.; Yin, Y. TiO₂/NiO Hybrid Shells: P-n Junction Photocatalysts with Enhanced Activity under Visible Light. J. Mater. Chem. A; 2015; 3, pp. 20727-20735. [DOI: https://dx.doi.org/10.1039/C5TA05839B]

139. Liu, J.; Ruan, L.; Adeloju, S.B.; Wu, Y. BiOI/TiO₂ Nanotube Arrays, a Unique Flake-Tube Structured p–n Junction with Remarkable Visible-Light Photoelectrocatalytic Performance and Stability. J. Chem. Soc. Dalt. Trans.; 2014; 43, pp. 1706-1715. [DOI: https://dx.doi.org/10.1039/C3DT52394B]

140. Dai, G.; Liu, S.; Liang, Y.; Luo, T. Synthesis and Enhanced Photoelectrocatalytic Activity of P-n Junction CO₃O₄/TiO₂ Nanotube Arrays. Appl. Surf. Sci.; 2013; 264, pp. 157-161. [DOI: https://dx.doi.org/10.1016/j.apsusc.2012.09.160]

141. Cheng, H.; Huang, B.; Dai, Y. Engineering BiOX (X = Cl, Br, I) Nanostructures for Highly Efficient Photocatalytic Applications. Nanoscale; 2014; 6, pp. 2009-2026. [DOI: https://dx.doi.org/10.1039/c3nr05529a] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/24430623]

142. Lv, K.; Guo, X.; Wu, X.; Li, Q.; Ho, W.; Li, M.; Ye, H.; Du, D. Photocatalytic Selective Oxidation of Phenol to Produce Dihydroxybenzenes in a TiO₂/UV System: Hydroxyl Radical versus Hole. Appl. Catal. B Environ.; 2016; 199, pp. 405-411. [DOI: https://dx.doi.org/10.1016/j.apcatb.2016.06.049]

143. Shi, H.; Zhang, T.; Li, B.; Wang, X.; He, M.; Qiu, M. Photocatalytic Hydroxylation of Phenol with Fe-Al-Silicate Photocatalyst: A Clean and Highly Selective Synthesis of Dihydroxybenzenes. Catal. Commun.; 2011; 12, pp. 1022-1026. [DOI: https://dx.doi.org/10.1016/j.catcom.2011.03.012]

144. Falch, E.A. Industrial Enzymes—Developments in Production and Application. Biotechnol. Adv.; 1991; 9, pp. 643-658. [DOI: https://dx.doi.org/10.1016/0734-9750(91)90736-F]

145. Chapman, J.; Ismail, A.E.; Dinu, C.Z. Industrial Applications of Enzymes: Recent Advances, Techniques, and Outlooks. Catalysts; 2018; 8, 238. [DOI: https://dx.doi.org/10.3390/catal8060238]

146. Yoshida, S.; Yoshikawa, A.; Terao, I. Microbial Production of Hydroquinone. J. Biotechnol.; 1990; 14, pp. 195-202. [DOI: https://dx.doi.org/10.1016/0168-1656(90)90008-Y]

147. Krastanov, A.; Alexieva, Z.; Yemendzhiev, H. Microbial Degradation of Phenol and Phenolic Derivatives. Eng. Life Sci.; 2013; 13, pp. 76-87. [DOI: https://dx.doi.org/10.1002/elsc.201100227]

148. Furuya, T.; Hirose, S.; Osanai, H.; Semba, H.; Kino, K. Identification of the Monooxygenase Gene Clusters Responsible for the Regioselective Oxidation of Phenol to Hydroquinone in Mycobacteria. Appl. Environ. Microbiol.; 2011; 77, pp. 1214-1220. [DOI: https://dx.doi.org/10.1128/AEM.02316-10] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/21183637]

149. Han, C.; Ye, Y.; Wang, G.; Hong, W.; Feng, C. Selective Electro-Oxidation of Phenol to Benzoquinone/Hydroquinone on Polyaniline Enhances Capacitance and Cycling Stability of Polyaniline Electrodes. Chem. Eng. J.; 2018; 347, pp. 648-659. [DOI: https://dx.doi.org/10.1016/j.cej.2018.04.109]

150. Li, G.; Xu, Y.; Pan, H.; Xie, X.; Chen, R.; Wu, D.; Wang, L. A Bimetallic Synergistic Effect on the Atomic Scale of Defect-Enriched NiV-Layered Double Hydroxide Nanosheets for Electrochemical Phenol Hydroxylation. J. Mater. Chem. A; 2022; 10, pp. 6748-6761. [DOI: https://dx.doi.org/10.1039/D1TA09412B]

151. Baravkar, M.D.; Prasad, B.L.V. Selective Electro-Oxidation of Phenol to 1,4-Hydroquinone Employing Carbonaceous Electrodes: Surface Modification Is the Key. New J. Chem.; 2022; 46, pp. 2518-2525. [DOI: https://dx.doi.org/10.1039/D1NJ04640C]

152. Zhang, W.; Li, Y.-J.; He, Y.; Zhang, S.; Li, H.-H.; Zheng, H.; Zhu, Q.-L. Membrane-Free Sequential Paired Electrosynthesis of 1,4-Hydroquinone from Phenol over a Self-Supported Electrocatalytic Electrode. Ind. Chem. Mater.; 2025.in press [DOI: https://dx.doi.org/10.1039/D4IM00067F]

153. FU, J.; JI, M.; WANG, Z.; JIN, L.; AN, D. A New Submerged Membrane Photocatalysis Reactor (SMPR) for Fulvic Acid Removal Using a Nano-Structured Photocatalyst. J. Hazard. Mater.; 2006; 131, pp. 238-242. [DOI: https://dx.doi.org/10.1016/j.jhazmat.2005.09.039] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/16266780]

154. Lu, C.; Chen, R.; Xing, W.; Jin, W.; Xu, N. A Submerged Membrane Reactor for Continuous Phenol Hydroxylation over TS-1. AIChE J.; 2008; 54, pp. 1842-1849. [DOI: https://dx.doi.org/10.1002/aic.11514]

155. Bazhenov, S.D.; Bildyukevich, A.V.; Volkov, A.V. Gas-Liquid Hollow Fiber Membrane Contactors for Different Applications. Fibers; 2018; 6, 76. [DOI: https://dx.doi.org/10.3390/fib6040076]