1. Introduction
Lignin is a primary component of lignocellulosic biomass and is one of the most abundant aromatic polymers on earth; as such, it has significant commercial potential [1,2]. Among various lignin model compounds, benzyl phenyl ether (BPE, Scheme 1 and Figure S1) has been widely used to represent the C–O (α-O-4) linkage in lignin. α-O-4 is generally considered to be the target bond during lignin depolymerization owing to it having the lowest bond dissociation energy [3]. The catalytic hydrogenolysis (HDL) of lignin is a key technology for lignin valorization, which enables the selective transformation of lignin into biofuel and aromatic chemicals [2,4].
Various catalysts based on noble metals such as supported Ru, Pd, and Pt catalysts have been reported to be effective for cleaving the C-O bond of BPE [5,6,7,8], but their high price and low abundance make them unfavorable for large-scale industrial production. Heteropoly acids, metal oxides, and modified kaolinite clay have been studied, [9,10,11]; however, exploration of a more affordable and efficient route for selectively cleaving BPE to aromatics under mild conditions is highly desirable. The more economically viable base metal catalysts, such as carbon-supported Ni [12,13] and Fe or PdFe catalysts, on various supports [14,15] have been reported for the hydrogenolysis of BPE but require further developments in the catalytic conditions. The use of H-donor solvents such as methanol, ethanol and 2-propanol via catalytic transfer hydrogenolysis conditions have been explored [16,17] as well as those in the aqueous/apolar phase [18], molten salt conditions [19], and alkali carbonates in superheated water [20]. Improvements in the HDL process have been attributed to effects, such as an increase in dispersion of the active phases, more adequate active phase–support interaction, acidity effects, and geometrical effects, resulting in greater exposure of the active sites, and, hence, increasing the overall catalytic activity and selectivity.
Supported NiMo catalysts have been used in various hydrotreating processes [21,22,23]. In this context, we have previously developed pillared clay-supported nickel–molybdenum catalysts (NiMo-PILC) for the hydrodeoxygenation (HDO) of guaiacol, a model compound of lignin and bio-oil [24,25]. Adsorption studies using infrared and neutron scattering techniques reveal that guaiacol was selectively adsorbed on the sulfided catalyst via H-bonding in coordination with the Ni-Mo-S site, resulting in 100% conversion and up to 77% phenol as the major product. Meanwhile, the adsorption of guaiacol on the reduced catalyst occurred both on the metal and catalyst support, forming methoxyphenate species, which in prolonged reaction times led to catalyst deactivation and lower catalyst activity. Following the successful guaiacol-to-phenol conversion, we aim to further investigate the potential application of NiMo-PILC catalysts for cleaving the C–O bond of BPE during the HDL process, a step towards HDO and the transformation of lignin to useful chemicals. The application of pillared clay-supported NiMo catalysts for the HDL of BPE and the comprehensive understanding of the interaction of BPE on the catalyst surface—an important aspect in catalyst optimization strategies—have not been explored previously. The total acidity, morphology, and metal distribution of the catalyst are discussed so as to understand the catalyst structure–activity relationship. The vibrational modes and interaction of BPE on the catalyst surface are analyzed using inelastic neutron scattering (INS) and quasielastic neutron scattering (QENS) techniques, which are powerful tools for understanding the structural dynamics and evolution of catalysts and the related surface chemistry [26,27,28,29]. Herein, we evaluate whether the selective adsorption of BPE on the NiMo-PILC catalysts can facilitate the C–O bond cleavage in BPE to provide a cost-effective alternative to the expensive precious metal catalysts, as well as the use of natural and industrially extracted bentonite clay for lignin valorization.
2. Results
2.1. Catalytic HDL of BPE
The catalytic HDL of BPE was performed using NiMo-PILC catalysts in their reduced (NiMoPR) and sulfided form (NiMoPS) under 20 bar H2 pressure and 573 K without the use of a solvent. The pillared clay catalyst support (PILC) was also tested for the reaction. Eight products were identified in the liquid product mixture, which is a result of different reaction pathways during the HDL such as the acid-catalyzed transalkylation (ALK), recombination (RCB), hydrocracking (HDC), and hydrodeoxygenation (HDO), as shown in Scheme 1. The products are toluene (1), phenol (2), alicyclics (3a, 3b), 2-benzyl toluene (4), benzylphenols (5a, 5b), o-cresol (6), o-xylene (7) and diphenylmethane (8), as summarized in Table 1 and Table 2. Benzene and benzylcyclohexane were also produced but in trace amounts and are not included in the mass balance calculation. It is noteworthy that benzyl alcohol was not detected in the product mixture, which suggests that the acid-catalyzed hydrolysis of BPE most likely did not occur under the applied condition or that benzyl alcohol rapidly underwent RCB to produce dimeric compounds once formed. The dimerization of benzyl species to form bibenzyl was not detected.
All of the catalysts gave a 100% conversion of BPE (Table 1). In the case of NiMoPS and NiMoPR, products (1) and (2) were identified as the main HDL products. NiMoPS gave an equimolar mixture of 30% (1) and (2), demonstrating selective Caliphatic–O bond (α-O-4) cleavage of BPE. Meanwhile, non-equimolar amounts of (1) and (2) were found for NiMoPR with 43 and 14% yield, respectively. This higher yield of (1) is expected to arise due to the consumption of HDL products towards ALK/RCB followed by HDC/HDO, resulting in monoaromatics and BTX compounds (1), (6), and (7). For both catalysts, the ALK-HDO product (8) was found to be most abundant (19% for NiMoPS and 20% for NiMoPR). With PILC, lower yields of (1) and (2) and a 32% yield of the dimeric compound (8) were obtained. PILC is known to have an acidic nature, and as expected, the acid-catalyzed ALK proceeded faster over PILC than the NiMo-PILC catalysts. These results show that the acidity of the catalyst significantly affects the product distribution, as found with NiMo-USY zeolite [22]. Hence, the acidic sites and their accessibility to the reactants and intermediates play an important role in the overall product selectivity during the HDL on NiMo-PILC catalysts.
In an attempt to increase the yield of HDL products (1) and (2), the reaction was also carried out at 523 and 623 K using NiMoPS as the catalyst. However, (1) and (2) were not obtained in equal amounts for both cases, and a higher amount of (2) was observed. Non-equimolar yields of (1) and (2) show that ALK and RCB of intermediates were significant, leading to the formation of stable aliphatic C-linked phenolic/deoxygenated dimers (4, 5a, 5b). Lowering the temperature resulted in an increased amount of (6), while elevating the temperature was only able to decrease (8) by a small amount. The results show that changing the temperature could not significantly suppress the formation of the dimeric compound (8) but affected the product distribution of monoaromatic and BTX products (1), (6), and (7). It was reported that the production of phenol and toluene appears to be almost the same at relatively lower levels of conversion, but the number of byproducts increases under more severe reaction conditions [30].
2.2. Catalyst Structure–Activity Relationship
2.2.1. TPD-NH3 Analysis
As the acidity of the NiMo-PILC catalysts influenced the HDL of BPE and product distribution, TPD-NH3 measurements were carried out to quantify the total acidity and evaluate the strength of the acid sites in NiMoPR, NiMoPS, and PILC, as well as their oxide precursor (NiMoPO) prior to reduction or sulfidation treatments. The total acidity is listed in Table 3, and the results show that NiMoPS (0.251 mmol g−1) has similar total acidity as PILC (0.235 mmol g−1), but their different catalytic performance indicates that there must be different ratios of strong and weak acid sites and/or a different ratio of Brønsted (B) and Lewis (L) acidity among them. A lower acid content was found for NiMoPR (0.189 mmol g−1) and NiMoPO (0.118 mmol g−1). This shows that the acidity of the PILC material decreased upon the introduction of NiMo metal and calcination but returned after sulfidation treatments. On the other hand, no significant change in the acid content was observed after reduction.
For all of the NiMo catalysts, two desorption peaks were observed at around 450 and 780 K, as illustrated in Figure 1, which are assigned to the weak and strong acid sites, respectively [31]. NiMoPS shows a much higher intensity in the high-temperature desorption peak compared to that of the low-temperature peak, indicating that strong acid sites are more dominant in the sulfided catalyst. NiMoPR shows almost the same intensity for both the weak and strong acid peaks, which implies that NiMoPR contains an almost equal distribution of the weak and strong acid sites. The presence of both B and L acidity in pillared clays has been previously demonstrated [11]. Pyridine FTIR is the best way to characterize Lewis and Brønsted acidity on catalysts; unfortunately, we do not currently have this capability.
Previous reports show that the conversion of BPE and total yield for the main HDL products increase with increasing surface acidity of the catalyst [18,22]. Furthermore, L acid sites promote the formation of monomeric aromatics such as benzene, phenol, and toluene during the decomposition of BPE, while B acid sites favor the formation of dimeric aromatics. In this study, NiMoPS has a higher total acidity compared to NiMoPR and PILC, which explains the higher selectivity of the sulfided catalyst towards HDL products and monomeric aromatics. Our findings show that NiMoPS with dominantly strong acid sites gave higher activity and selectivity for the HDL reaction.
2.2.2. SEM and HRTEM Analysis
In order to investigate the morphologies of the catalyst and confirm the dispersion of the NiMo metals on PILC, the NiMo-PILC catalysts were observed by SEM and HRTEM analyses. The SEM images and area selected for SEM EDS mappings of the reduced and sulfided catalyst are shown in Figures S2 and S3, respectively. A uniform distribution and efficient loading of Ni (green) and Mo (orange) on the surface of PILC was clearly seen for both catalysts, S (yellow) was homogeneously distributed in the sulfided catalyst. Moreover, irregular porous structures were seen for both the NiMoPR and NiMoPS.
The distribution of the metal sulfides is crucial in determining their activity and selectivity under the reaction conditions. The HRTEM images of the sulfided NiMo catalyst shown in Figure 2 revealed the dispersion of the active NiMoS2 phase. The average slab length (LA) was calculated to be 6.1 and 10.4 nm and was taken in two different image locations, and the average stacking layer number (NA) of the NiMoS2 particles was found to be 6.0 and 9.5. The reaction pathways of the sulfided NiMo catalyst are known to be related to the lamellar length and stacking layers of the NiMoS2 active component. The shorter slab length and more stacking layers have proven to favor direct desulfurization and hydrogenation activity over the NiMo-Y zeolite catalyst (LA = 9.9–10.7 nm, NA = 3.7–5.2) [23]. This trend was also the same for hydrotreating BPE on a NiMo-USY zeolite (LA = 4.1 nm, NA = 4.2) [22]. A shorter slab length can produce more sulfur vacancies, which favor the reaction; on the contrary, more stacking layers could result in the aggregation of the active NiMoS2 components with higher hydrogenation activity.
2.3. Neutron Scattering and Computational Studies
As far as we are aware, there are no reported assignments of either the structure or the vibrational spectra of BPE. Thus, as a first step to understanding the interaction of BPE with the catalyst’s surface, we have carried out a comprehensive investigation of the two-dimensional potential energy surface (2D PES) of BPE and its vibrational spectra. Figure 3 shows the BPE 2D-PES as a function of the torsions about the phenyl–O and phenyl–CH2 bonds.
Room temperature corresponds to ~200 cm−1; thus, it would appear in Figure 4 that the planar Cs conformer was the lowest energy state. Surprisingly, this turns out not to be the case, as the calculation of the vibrational spectrum produces one imaginary mode, the torsion about the phenyl–CH2 bond. The lowest energy structure is a C1 conformer with the phenyl ring attached to the methylene group twisted out of the plane, and the dihedral angle between the planes of the phenyl rings is 35.3° (see Figure S1). The energy difference between the Cs and C1 conformers is small, only 6 meV (48.4 cm−1), so both conformers will be present at room temperature. To check that the Cs conformer is in the ground state, we have calculated the infrared and INS spectra of both conformers, and the results are shown in Figure 4.
It can be seen that in both cases, the C1 conformer provides a better match to the experimental data, this is most apparent in the 0–500 cm−1 region. In particular, in the infrared spectrum, the band at ~500 cm−1 and in the INS the pattern of bands in the 200–400 cm−1 range are in much better agreement with the data. It should be noted that the calculations are for an isolated, i.e., gas phase, molecule, whereas the experimental spectra are for the solid state, showing that the conformation is the same in both phases.
The assignment of the phenyl modes of monosubstituted benzenes is a subject that has been investigated multiple times. An enlightening discussion of the advantages and disadvantages of the various schemes has been provided by Gardner and Wright [32]. They introduced a new assignment (the modes are labeled ℳ1 to ℳ30) that avoids the pitfalls of the previous methods and we have followed their conventions. The form of the modes and the typical ranges are reproduced from [32] in Figure S4 and Table S1. Table 4 lists the observed and calculated transition energies with the assignments. It can be seen that in most cases, the two phenyl rings behave independently. The mode descriptions are necessarily limited; those involving the –CH2–O– link usually have significant contributions from the phenyl modes closest in energy.
A comparison of the INS spectra of BPE adsorbed on PILC, NiMoPR, and NiMoPS is shown in Figure 5. At first glance, it seems that the spectra are similar in all three samples, but a more careful look into the data shows that this is not the case. As assigned in Table 4, the region < 800 cm−1 is dominated by the in-plane and out-of-plane ring deformation modes of BPE, by which a number of these modes are less pronounced after adsorption. This suggests that BPE interacts with the catalysts in various configurations. Previously, we have reported there are at least six configurations involving the adsorption of guaiacol on NiMoS2 [25]. This might also be the case for BPE, although further elaboration requires DFT calculations, which will be performed in our future work.
The CH2 out-of-plane bend ℳ20(B) ring methylene group in BPE was found to be at 250 cm−1. No shift of this band was seen for PILC and NiMoPS, which indicates that BPE is weakly adsorbed on the catalyst surfaces, as was also found for guaiacol [24]. BPE is weakly chemisorbed on NiMoS2, hence, the preferable adsorption sites are not limited to coordinatively unsaturated sites (CUSs) on Mo- and Ni-edge surfaces [33], but they also might involve the basal plane of MoS2, where our DFT study has demonstrated benzene and guaiacol physiosorbed on the MoS2 basal plane via van der Waals interactions [25]. Likewise, a weak BPE adsorption on PILC is presumably owing to weak bonding between BPE and siloxane surfaces. A similar observation has been reported in a DFT study of phenol and toluene adsorption on the basal surface of kaolinite [34]. On the contrary, for NiMoPR, a shift from 250 to 259 cm−1 is detected and demonstrates that BPE is chemisorbed on the catalyst [24].
In the region of 800–1200 cm−1, the peaks are largely the in-plane and out-of-plane C–H bend modes. The silanol groups on the clay surface are also observed in this region at ~930 cm−1. Interestingly, no shifts were observed for the out-of-plane C–H bend ℳ16(B) and silanol peaks at 931 cm−1 for both PILC and NiMoPS, but a shift to 953 cm−1 was detected for NiMoPR. A peak shift towards a higher wavelength demonstrates a stronger interaction of the substrate with the catalyst. In Figure 6, we illustrate some plausible interactions of BPE in various configurations on the surface of PILC, NiMoPR, and NiMoPS. For PILC, BPE interacts weakly through van der Waals interactions with siloxane groups on the basal plane of PILC, as well as with the silanol groups located on the edge sites of PILC via H-bonding interaction (Figure 6a). In the case of NiMoPR, a strong interaction between BPE and the catalyst is formed due to covalent bonds between the C atoms of BPE and Ni or Mo atoms on the NiMoPR surface (Figure 6b). This consideration is made based on previous DFT results that demonstrate that several aromatic compounds (benzene, phenol, toluene, and m-cresol) are adsorbed as flat-lying aromatics on the surface of 4d and 5d noble metals [35]. For NiMoPS, BPE weakly interacts with the basal plane of MoS2 via van der Waals interaction as well as on the edge without CUS. Another possibility is the interaction by covalent bonding on the edge with CUS, although we predict that this would be less likely, as no peak shifts were observed for NiMoPS (Figure 6c).
The modes in the 1200–2000 cm−1 region show the ring C-C stretch peaks but are only seen with low intensity. Overall, the INS spectra suggest that BPE is weakly adsorbed on PILC and NiMoPS via H-bonding and van der Waals interaction but is strongly chemisorbed on NiMoPR due to covalent bonding. In connection to practical catalyst design, we emphasize that strong chemisorption as observed on NiMoPR, may form a strongly held carbonaceous phenate species, and is predicted to be a source of severe catalyst poisoning. Meanwhile weakly adsorbed BPE on NiMoPS is more favorable as it allows better molecular mobility across the catalyst surface. This mobility is crucial for ensuring effective access to catalytic sites and promoting subsequent reactions with hydrogen during the HDL process. Hence, sulfidation treatment is an important synthesis step in order to design a stable and effective catalyst for the HDL of BPE. The infrared spectra in the 1200–1800 cm−1 region showing the ring C-C stretch modes can be found in Figure S5 and show that the peaks are more pronounced in NiMoPS compared to NiMoPR and PILC.
In addition to the vibrational studies using INS, we also investigated the effect of sulfidation of the NiMo-PILC towards the dynamics of BPE using QENS, and the results are shown in Figure 7. The measurements performed were those for PILC with adsorbed BPE (red), NiMoPR with adsorbed BPE (orange), NiMoPS with adsorbed BPE (green) and pure BPE (blue). A comparison of these measurements has enabled us to see the effect of the sulfided metal on the diffusion, allowing a distinction between motion on the support and on the NiMo component. For each sample, we measured an elastic window scan from base temperature (10 K) to 373 K (BPE melts at 313 K and boils at 559 K). The results of normalized data at 350 K reveal that more motion was observed for the BPE adsorbed on the sulfided NiMoPS catalyst when compared to that adsorbed on PILC and the reduced NiMoPR catalyst, which promotes the higher activity of NiMoPS for the HDL reaction.
3. Materials and Methods
3.1. Materials
BPE (98%) and reference products (>99%) were purchased from Sigma-Aldrich (Gillingham, Dorset, UK) and used without further purification. Aluminum chloride (>99%), ammonium heptamolybdate tetrahydrate (>99%), nickel nitrate hexahydrate (>99%), and sodium hydroxide (>99%) were obtained from Sigma-Aldrich. The PILC catalyst support was synthesized from a bentonite clay (BT) precursor, which was purchased from Sigma-Aldrich.
3.2. Synthesis of PILC and PILC-Supported NiMo Catalyst
The synthesis of PILC and NiMo-PILC catalysts was carried out following the procedures we previously reported [24].
3.3. Catalytic Testing
The NiMo clay catalyst (0.05 g, 5 wt %) was performed in a homemade high-pressure autoclave (similar design to the Parr Series 4790 Pressure Vessel Systems, 25–100 mL) equipped with a magnetic stirrer. BPE (1 g) was added, and the reaction was carried out at varying temperatures (see Table 1 and Table 2) at 20 bar H2 pressure for 6 h with stirring at 400 rpm. The liquid product was then extracted using dichloromethane and analyzed based on a GC area ratio method on an Agilent GC/MS 7890B (Santa Clara, CA, USA) system packed with an HP-5MS UI column (40–90 °C, 10 °C/min, hold 4 min; 90–200 °C, 5 °C/min, hold 1 min; 200–300 °C, 20 °C/min, hold 4 min; 1 mL/min gas flow) and an Agilent 7890A GC/FID system equipped with a DB-WAX column (40–220 °C, 10 °C/min, hold 1 min; 1 mL/min gas flow).
3.4. Catalyst Characterisation
The total acidity of the NiMo-PILC catalysts and their precursors were determined by NH3 temperature-programmed desorption (NH3-TPD) on a Micromeritics ChemiSoft TPx V1.03 (Norcross, GA, USA). Before the adsorption of ammonia, the samples were treated under helium at 673 K for 30 min. The samples were then cooled and treated with a NH3 flow for 30 min at 373 K and purged with a He flow for another 30 min. The NH3-TPD was run between 373 and 973 K at 10 K/min, and the final temperature was held for 10 min to ensure total ammonia desorption. Detection was performed by an online gas chromatograph with a thermal conductivity detector. Scanning electron microscopy (SEM) was performed using a Jeol JSM-IT200 (Tokyo, Japan) and high-resolution transmission electron microscopy (HRTEM) was carried out on a Hitachi H7650 (Tokyo, Japan) at 19 kV.
3.5. Neutron Scattering Measurements
INS and QENS experiments were carried out at the ISIS Neutron and Muon Source, Oxfordshire, United Kingdom. The catalyst samples (ca. 10 g) were packed into a stainless steel or Inconel can and dried under a flow of helium gas at 473 K for 2 h in a gas line system prior to the analyses. BPE (1 g) was mechanically loaded into the catalyst at room temperature and heated for 4 h at 423 K to give the BPE-adsorbed catalyst (dosed samples). The INS experiments were performed on TOSCA, a broadband (30−4000 cm−1) INS spectrometer. The clean and dosed catalyst samples (ca. 10 g) were placed in a stainless steel or Inconel can and loaded in a closed cycle refrigerator (CCR) cryostat. All spectra were measured at 20 K for 12 h. For additional vibrational studies, the infrared spectra of the clean and dosed samples were analyzed using a Bruker Vertex 80V FTIR. The QENS measurements were carried out on IRIS, a high-resolution time-of-flight instrument, with the energy transfer measured in a window of −0.5 to 0.5 meV and an energy resolution of 17.5 μeV. Cooled pyrolytic graphite (PG002) was used as the analyzer crystal. The clean and dosed catalyst samples (ca. 8 g) were transferred in a glove box to cylindrical aluminum containers of annular geometry. The cells were placed in a CCR cryostat, and measurements were taken between base temperature (~5 K) and 373 K.
3.6. Computational Studies
All the computational studies used Gaussian09 [36], with GaussView05 [37] used to prepare the input files and visualize the results. The 2D potential energy surface (PES) of BPE was surveyed as a function of the torsions about the phenyl–O and phenyl–CH2 bonds using a relaxed potential energy scan. Owing to the large number of data points required (1444), the small basis set 3-21G was used with the B3LYP functional. For calculations of the vibrational spectra, the larger 6-311G(d) basis set with the B3LYP functional was used. The calculated transition energies >350 cm−1 have been scaled by 0.98. The INS spectra were generated from the atomic displacements in each mode that are part of the Gaussian09 output with ACLIMAX [38]. For isolated molecule calculations, the INS intensity for the lowest energy modes is over-estimated because they are not damped by the crystalline environment, which is what happens for the experimental spectrum. This results in an excessively large Debye–Waller factor and the higher energy modes are overly attenuated. To compensate for this, the intensity of the modes below 200 cm−1 has been reduced by two-thirds before the calculation of the INS spectrum.
4. Conclusions
NiMo-pillared clay catalysts in their reduced (NiMoPR) and sulfided (NiMoPS) forms were tested for the hydrogenolysis (HDL) of benzyl phenyl ether (BPE), a model for the important α-O-4 linkage in lignin. Under 20 bar H2, 573 K for 6 h, all catalysts achieved 100% BPE conversion but showed different product distributions. NiMoPS demonstrated superior selectivity, yielding an equimolar mixture of toluene (30%) and phenol (30%) via selective cleavage of the Caliphatic–O bond. NiMoPR yielded 43% toluene and 14% phenol, while the clay support (PILC) produced mainly diphenylmethane (32%).
We note that conducting the catalyst testing at a range of conversions (rather than only at 100% conversion) would be informative, particularly as products (3)–(8) result from reactions of the products of the initial cleavage of the C–O bond. This will depress the quantity of the desired monoaromatic products. Nonetheless, the data show distinct differences between NiMoPS, NiMoPR, and PILC. This is relevant information for future development of the catalysts.
Neutron scattering and computational studies revealed that BPE interacts weakly with NiMoPS and PILC via H-bonding and van der Waals interactions, enabling better molecular mobility across the catalyst surface. This mobility is crucial for ensuring effective access to catalytic sites and promoting subsequent reactions with hydrogen during the HDL process. On the other hand, NiMoPR strongly chemisorbs BPE, likely forming carbonaceous phenate species that hinder the activity. The higher total acidity and abundance of strong acid sites in NiMoPS favor selective cleavage of the C–O bond and enhance HDL performance. NiMo clay catalysts provide a cost-effective alternative to expensive precious metal catalysts. The catalyst is synthesized using simple impregnation and sulfidation methods and uses the natural and industrially extracted bentonite clay, which we believe has potential application for lignin valorization in future biorefineries.
Conceptualization, I.B.A. and S.F.P.; funding acquisition, I.B.A.; investigation, I.B.A., M.A.F., F.O., F.A., N.R., G.K.S., I.P.S. and S.F.P.; methodology, I.B.A., I.P.S. and S.F.P.; supervision, I.B.A., I.P.S. and S.F.P.; writing—original draft, I.B.A. and F.O.; writing—review and editing, I.B.A., I.P.S. and S.F.P. All authors have read and agreed to the published version of the manuscript.
The neutron scattering data used in this study are available at the URLs given in references [
The STFC Rutherford Appleton Laboratory is thanked for providing access to neutron beam facilities via RB1820250 (TOSCA) [
The authors declare no conflicts of interest.
Footnotes
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Enlarge this image.Scheme 1. Reaction pathway contributing to the HDL of BPE using NiMo-PILC catalysts.
Enlarge this image.Figure 1. NH3-TPD profiles for (a) BT clay, (b) PILC, (c) NiMoPO, (d) NiMoPR, and (e) NiMoPS.
Enlarge this image.Figure 2. HRTEM images (a,c) at two different locations and their respective slab length distributions (b,d) of the NiMoPS catalyst.
Enlarge this image.Figure 4. Comparison of observed and calculated (a) infrared and (b) INS spectra of BPE. In each case, the experimental spectrum is in the middle, with the Cs and C1 conformers above and below it, respectively.
Enlarge this image.Figure 5. INS spectra of BPE adsorbed on the catalysts: (a) PILC, (b) NiMoPR, and (c) NiMoPS.
Enlarge this image.Figure 6. Schematic illustration of possible BPE configurations interacting with (a) PILC, (b) NiMoPR, and (c) NiMoPS.
Hydrogenolysis of BPE using various NiMo-PILC catalysts.
| Catalyst | Temperature | Conversion | Product Distribution/% | |||||||
|---|---|---|---|---|---|---|---|---|---|---|
| (1) | (2) | (3) | (4) | (5) | (6) | (7) | (8) | |||
| NiMoPS | 573 | 100 | 30 | 30 | 4 | 5 | 4 | 3 | 5 | 19 |
| NiMoPR | 573 | 100 | 43 | 14 | 5 | 6 | 3 | 1 | 8 | 20 |
| PILC | 573 | 100 | 22 | 29 | 3 | 5 | 4 | 2 | 3 | 32 |
Hydrogenolysis of BPE using the sulfided NiMoPS catalyst at various temperatures.
| Catalyst | Temperature | Conversion/% | Product Distribution/% | |||||||
|---|---|---|---|---|---|---|---|---|---|---|
| (1) | (2) | (3) | (4) | (5) | (6) | (7) | (8) | |||
| NiMoPS | 523 | 100 | 11 | 52 | 2 | 2 | 2 | 11 | 2 | 18 |
| NiMoPS | 573 | 100 | 30 | 30 | 4 | 5 | 4 | 3 | 7 | 19 |
| NiMoPS | 623 | 100 | 31 | 41 | 2 | 4 | 3 | 3 | 4 | 12 |
Total acidity of various NiMo-PILC catalysts determined by NH3-TPD.
| Catalyst | Acidity (mmol g−1) |
|---|---|
| NiMoPS | 0.251 |
| NiMoPR | 0.189 |
| NiMoPO | 0.118 |
| PILC | 0.235 |
Observed and calculated INS and infrared transition energies of BPE.
| Observed | Calculated a | Description b,c | ||
|---|---|---|---|---|
| INS | Infrared | /cm−1 | Infrared Intensity | |
| 23 | 0.48 | B c ring–CH2 torsion | ||
| 37 | 0.31 | A ring out-of-plane bend | ||
| 72 | 0.12 | O–CH2–B ring in-plane bend | ||
| 94 | 2.78 | O–CH2 torsion | ||
| 188s d | 188w | 188 | 1.60 | CH2–O–A ring in-plane bend |
| 245s | 239w | 228 | 1.67 | CH2 out-of-plane bend ℳ20(B) |
| 258s | 250 | 0.30 | O out-of-plane bend ℳ20(A) | |
| 336vs | 333w | 309 | 1.17 | O–CH2–B ring in-plane bend ℳ30(B) |
| 406vs | 405w | 407 | 0.59 | Out-of-plane ring deformation ℳ14(B) |
| 414/423w | 415 | 0.00 | Out-of-plane ring deformation ℳ14(A) | |
| 425s | 439 | 2.05 | O-A ring in-plane bend ℳ30(A) | |
| 507s | 502m | 496 | 6.67 | Out-of-plane ring deformation ℳ19(B) |
| 517m | 515m | 508 | 11.62 | Out-of-plane ring deformation ℳ19(A) |
| 532w | 532w | 532 | 0.31 | In-plane ring deformation ℳ11(A) + ℳ11(B) out of phase |
| 616m,br | 610w | 618 | 1.30 | In-plane ring deformation ℳ29(A) |
| 619sh | 624 | 0.32 | In-plane ring deformation ℳ29(B) | |
| 629w | 627m | 631 | 5.59 | In-plane ring deformation ℳ11(A) + ℳ11(B) in phase |
| 688s | 687 | 24.57 | Out-of-plane ring deformation ℳ18(A) | |
| 695s | 696s | 696 | 31.63 | Out-of-plane ring deformation ℳ18(B) |
| 750s | 735 | 36.58 | Out-of-plane ring deformation ℳ17(B) | |
| 761s | 742vs | 748 | 74.01 | Out-of-plane ring deformation ℳ17(A) |
| 800w | 803 | 7.83 | CH2–B ring stretch + O–A ring stretch out-of-phase ℳ10(A) + ℳ10(B) | |
| 816m,br | 811w | 806 | 0.07 | Out-of-plane C–H bend ℳ13(B) |
| 854 | 836 | 0.44 | Out-of-plane C–H bend ℳ13(A) | |
| 856m | 848 | 18.95 | CH2–B ring stretch + O–A ring stretch in-phase ℳ10(A) + ℳ10(B) | |
| 882m | 877w | 871 | 8.21 | Out-of-plane C–H bend ℳ16(A) |
| 921m | 915m | 897 | 6.32 | Out-of-plane C–H bend ℳ16(B) |
| 957sh | 931 | 0.04 | Out-of-plane C–H bend ℳ12(B) | |
| 977m | 944 | 0.12 | Out-of-plane C–H bend ℳ12(A) | |
| 953 | 0.23 | Out-of-plane C–H bend ℳ15(A) | ||
| 992m | 970 | 0.60 | Out-of-plane C–H bend ℳ15(B) | |
| 990m | 992 | 1.64 | Out-of-plane C–H bend ℳ9(A) | |
| 999 | 1.08 | Out-of-plane C–H bend ℳ9(B) | ||
| 1011s | 1014 | 9.29 | CH2 rock | |
| 1028m | 1024 | 6.83 | In-plane ring deformation ℳ8(A) | |
| 1027s | 1032 | 14.98 | In-plane ring deformation ℳ8(B) | |
| 1077s | 1040 | 73.64 | O–CH2 stretch | |
| 1082m | 1085 | 11.87 | In-plane C–H bend ℳ28(A) | |
| 1092 | 4.91 | In-plane C–H bend ℳ28(B) | ||
| 1147w | 1159 | 6.22 | In-plane C–H bend ℳ27(A) | |
| 1158m | 1162sh | 1163 | 0.12 | In-plane C–H bend ℳ27(B) |
| 1172m | 1169s | 1176 | 24.95 | In-plane C–H bend ℳ7(A) |
| 1183 | 3.17 | In-plane C–H bend ℳ7(B) | ||
| 1208 | 0.15 | In-plane C–H bend ℳ6(B) | ||
| 1240vs,br | 1243 | 302.63 | In-plane C–H bend ℳ6(A) | |
| 1222m | 1253 | 83.72 | CH2 twist | |
| 1287w | 1303 | 10.37 | Ring C–C stretch ℳ25(A) + ℳ25(B) | |
| 1305sh | 1300m | 1312 | 27.53 | Ring C–C stretch ℳ25(A) + ℳ25(B) |
| 1329m | 1323w | 1335 | 3.45 | Ring C–C stretch ℳ26(B) |
| 1335w | 1336 | 9.18 | Ring C–C stretch ℳ26(A) | |
| 1378m | 1376s | 1398 | 56.73 | CH2 wag |
| 1457m | 1467/1454m | 1463 | 16.56 | Ring C–C stretch ℳ24(B) |
| 1465 | 0.77 | Ring C–C stretch ℳ24(A) | ||
| 1484sh | 1491 | 78.04 | CH2 scissors | |
| 1486m,br | 1496s | 1505 | 22.46 | Ring C–C stretch ℳ5(A) + ℳ5(B) |
| 1509 | 44.73 | Ring C–C stretch ℳ5(A) + ℳ5(B) | ||
| 1590w,br | 1585s | 1598 | 30.67 | Ring C–C stretch ℳ23(A) |
| 1602 | 0.83 | Ring C–C stretch ℳ23(B) | ||
| 1598vs | 1618 | 87.90 | Ring C–C stretch ℳ4(A) | |
| 1623 | 0.91 | Ring C–C stretch ℳ4(B) | ||
| 2867m | 2931 | 29.63 | CH2 symmetric C–H stretch | |
| 2907m | 2974 | 32.80 | CH2 asymmetric C–H stretch | |
| 3091 | 8.58 | Phenyl C–H stretch ℳ3(B) | ||
| 3099 | 2.78 | Phenyl C–H stretch ℳ3(A) | ||
| 3100 | 1.61 | Phenyl C–H stretch ℳ22(B) | ||
| 3107 | 17.16 | Phenyl C–H stretch ℳ22(A) | ||
| 3013w | 3111 | 32.38 | Phenyl C–H stretch ℳ2(B) | |
| 3036m | 3123 | 63.73 | Phenyl C–H stretch ℳ2(A) | |
| 3048vw | 3123 | 14.67 | Phenyl C–H stretch ℳ21(B) | |
| 3057vw | 3131 | 15.56 | Phenyl C–H stretch ℳ21(A) | |
| 3097vw | 3133 | 9.26 | Phenyl C–H stretch ℳ1(B) | |
| 3101vw | 3141 | 9.05 | Phenyl C–H stretch ℳ1(A) |
a Transition energies > 350 cm−1 have been scaled by a factor of 0.98. b The description of the phenyl modes uses the Gardner and Wright ℳ notation [
Supplementary Materials
The following supporting information can be downloaded at
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Details
; Aulia, Fauzan 2 ; Rinaldi, Nino 2
; Sunnardianto, Gagus K 3 ; Silverwood, Ian P 4
; Parker, Stewart F 4
1 Research Center for Chemistry, National Research and Innovation Agency, KST BJ Habibie, Tangerang Selatan 15314, Banten, Indonesia;
2 Research Center for Chemistry, National Research and Innovation Agency, KST BJ Habibie, Tangerang Selatan 15314, Banten, Indonesia;
3 Research Center for Quantum Physics, National Research and Innovation Agency, KST BJ Habibie, Tangerang Selatan 15314, Banten, Indonesia;
4 ISIS Neutron and Muon Source, STFC Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK;