Hydrophilic Ti-MWW for catalyzing epoxidation of allyl alcohol
Abstract
Titanosilicates are widely applied in the alkene epoxidation reactions with high reaction rate and selectivity to desired products. Their catalytic performance depends on the structure topology, the micro-environment of Ti active sites, and the hydrophobicity/hydrophilicity of zeolite framework. Herein, we focus on a hydrophilic substrate of allyl alcohol (AAL) and investigated catalytic performance of four titanosilicates (TS-1, Ti-MOR,
Keywords
INTRODUCTION
Glycidol (GLY) is an important oxygenated derivative of allyl alcohol (AAL), which is mainly used as a stabilizer in natural oils, emulsion breakers, and dye delamination agents. Generally, GLY is produced by the chloropropane method or the epoxidation of AAL. However, the chloropropane method leads to the generation of chlorine waste, causing serious environmental problems, while the epoxidation method using V2O5, Cr2O3, and WO3 as catalysts has problems in regeneration and reusability[1-5]. Therefore, developing highly active and reusable catalyst to construct a green process for GLY production is desirable.
Zeolite, as a kind of representative solid acid catalyst, is widely used in the petrochemical industry[6]. The framework Si or Al can be partially replaced by the transition metals, such as Ti and Sn, to fabricate heteroatom-containing zeolites, which exhibit high activity in selective oxidation reactions[7-10]. TS-1 zeolite, with Ti isomorphously incorporated into MFI structure, is the first-generation titanosilicate and has been used in several industrial reactions using H2O2 as the oxidant, such as cyclohexanone ammoximation and propene epoxidation reactions[11-13]. However, the medium-size 10-membered ring (MR) pores of TS-1 suffer diffusion restrictions when processing large-size substrates[14]. Afterward, Ti-MWW with 12MR large cavities and surface half cups was developed. Ti-MWW exhibits higher conversion than TS-1 in the propylene and cyclohexene epoxidation[15]. The catalytic activity of Ti-MWW in olefin epoxidation reactions can be further enhanced by post-modifications, such as fluoride treatment or piperidine
For the titanosilicate/H2O2 catalytic system, the pore size of titanosilicate affects the mass transfer of guest molecules (both reactants and products), while the framework hydrophobicity affects the diffusion rate and enrichment ability of substrate molecules (including organic substrates and H2O2)[8]. Na et al. converted surface Si-OH groups in layered TS-1 zeolite into Si-F groups through the NH4F treatment, which effectively improved the epoxidation activity in 1-hexene epoxidation reaction because of the enhancement of framework hydrophobicity[20]. Wang et al. increased the hydrophilicity of TS-1 to enrich H2O2 around Ti sites, resulting in higher catalytic activity by improving the H2O2 activation rate[21]. Bregante et al. reported that the large number of Si-OH groups in Ti-Beta near the Ti active centers disrupted the transition state of epoxidation reaction by hydrogen bonding with H2O molecular clusters, generating an entropy increase for the reaction. The highly hydrophilic Ti-Beta gave an epoxidation turnover rate that was 100 times larger than that of hydrophobic Ti-Beta in the 1-hexene epoxidation reaction[22-25].
In addition to the intrinsic Ti activity and the confinement environment from zeolitic structural properties, the solvent effect is also a factor worthy of attention. Solvents can facilitate mass and heat transfer, and more importantly, the protic solvents can participate in the construction of the 5-MR intermediate with Ti-OOH active species. To form Ti-OOH active species, the H2O2 molecules need to undergo hydrogen proton transfer[26,27]. Bonino et al. proposed that protic solvent molecules (H2O or MeOH) could act as hydrogen proton carriers to facilitate the formation of Ti-OOH by forming hydrogen bonding networks with H2O2 and Ti-OH in the reaction system[28]. Theoretical calculations by Wang et al. revealed that the non-protic solvent MeCN has no effect on the reaction path and kinetics, while the protic solvent MeOH can co-adsorb with H2O2 on Ti active sites through hydrogen bonding to reduce the dissociation energy of H2O2 and promote the hydrogen proton transfer[29]. Wang et al. revealed that the smaller the molecular size of a protic solvent, the less effect of the formed 5MR intermediate on the diffusion of the substrate[30]. Thus, water is the preferred solvent once it matches the reaction system of alkene epoxidation. On the one hand, it is a small-size molecule, imposing fewer diffusion constraints. On the other hand, H2O does not cause environmental pollution as a solvent[31,32].
In previous reports, several titanosilicates were evaluated in the catalytic epoxidation of AAL; among them, Ti-MWW showed high GLY yields[1]. To construct a more efficient catalytic system for AAL epoxidation reaction, a modified Ti-MWW catalyst, obtained by PI-assisted structural rearrangement, was used as a catalyst in the present study, and its epoxidation activity was compared with Ti-MWW, TS-1, and Ti-MOR. Re-Ti-MWW exhibited the highest turnover rate and GLY selectivity among all the four catalysts. After the PI-assisted structure rearrangement, some of the tetrahedrally coordinated Ti species were transformed into hexa-coordinated ones with higher activity by interacting with PI molecules. The 3D to 2D structural transformation increased the amount of surface Si-OH groups, thus increasing framework hydrophilicity and altering the solvent effect for the AAL epoxidation reaction. Despite having the same layer structure as Ti-MWW, the preferred solvent changed from MeCN for Ti-MWW to the greener water for Re-Ti-MWW in the AAL epoxidation reaction. The reaction kinetics of AAL epoxidation over Ti-MWW and
EXPERIMENTAL
Synthesis of different titanosilicates
Ti-MWW zeolites were hydrothermally synthesized as described previously[33], with a molar composition of 1.0 SiO2 : 0.03 TiO2 : 1.4 PI : 0.67 B2O3 : 19 H2O, where boric acid was used as the crystallization agent and PI as the structure-directing agent. The Si and Ti sources were silica sol solution (30 wt%) and tetrabutyl orthotitanate (TBOT), respectively. The synthetic gel was heated at 443 K for 7 days under dynamic conditions. The product was collected by filtration, washing with distilled water, and drying at 373 K for 12 h. Then, an acid treatment by 2.0 M HNO3 aqueous solution was performed with a solid-to-liquid weight ratio of 1:50 at 413 K for 12 h to remove extra-framework Ti, followed by calcination at 823 K for 6 h. For comparison, TS-1 zeolites were prepared following a reported protocol[18]. Ti-MOR zeolites were obtained by commercial H-MOR combining dealumination and TiCl4 treatment, according to the previous work[34,35].
PI-assisted post-treatment of Ti-MWW
Re-Ti-MWW zeolites were prepared as described previously[16]. Subsequently, 2.84 g of PI was added to
Materials characterization
The crystalline structures of zeolites were confirmed using an Ultima IV X-ray powder diffractometer (XRD) from Rigaku, with a Ni-filtered CuKα X-ray source (λ = 1.5406 Å), and the voltage and current were 35 kV and 25 mA, respectively. The content of organic species and water in catalysts was determined by a TGA/SDTA 851 thermogravimetric (TG) analyzer from Mettler Toledo. The sample was heated from 303 to 1,073 K in air. The solid-state NMR spectra of catalysts were measured using a VNMRS-400 MB NMR spectrometer manufactured by VARIAN[13]. C MAS NMR spectra were determined using adamantane as a standard at 100.54 MHz and 5 kHz[29]. Si MAS NMR spectra were determined using [(CH3)3SiO]8SiO12 as a standard at 79.43 and 3 kHz. Scanning electron microscope (SEM) images were obtained from a Hitachi
Diffusivity measurement
The diffusivity of AAL over various titanosilicates was determined by gravimetric analysis using a TG analyzer. The catalyst was pre-treated at 423 K under nitrogen for 2 h and then cooled down to 313 K to keep the weight baseline stable. Subsequently, AAL was brought into the TG by nitrogen gas (50 mL·min-1) at 313 K for 2 h. Fick’s second law was used to calculate the effective diffusion coefficient. At the beginning of the adsorption, the formula can be well approximated as follows:
Catalytic performance
Batchwise allyl alcohol epoxidation
The AAL epoxidation was performed in a 35 mL quartz reaction tube. In a typical experiment, 30 mg catalyst, 30 mmol H2O2 (30 wt% aqueous solution), 30 mmol AAL, and 5 mL solvent were added into the reaction tube. The reaction solution was stirred at 313 K for 0.5 h. After reaction, the catalyst was separated by centrifugation. Cyclopentanone was added as the internal standard, and the liquid-phase product was analyzed by gas chromatography (Shimadzu 2014, FID detector) equipped with a Rtx-Wax capillary column. The residual H2O2 was titrated with 0.05 M Ce(SO4)2 aqueous solution.
Glycidol hydrolysis reaction
The GLY hydrolysis reaction was performed in a 35 mL quartz reaction tube. Following that, 10 mmol GLY, 5 mL solvent, 10 mmol H2O2 (30 wt% aqueous solution), and 100 mg catalyst were introduced into the reaction tube and stirred at 313 K for 20-300 min. After reaction, the catalyst was separated by centrifugation, and the remaining reaction solution was analyzed by gas chromatography.
Continuous liquid-phase allyl alcohol epoxidation
The continuous epoxidation reaction of AAL was performed in a slurry bed reactor. The reaction temperature was controlled by a water bath [Supplementary Scheme 1]. The AAL/H2O2/H2O solution was fed via a peristaltic pump to the reactor, where 1 g of catalyst and 35 mL of water were added in advance at 40 °C. The gauze was used as a filter for solid-liquid separation, and the liquid product was analyzed by gas chromatography.
RESULTS AND DISCUSSION
Characterization of different zeolites
The XRD patterns revealed that Ti-MWW, TS-1, and Ti-MOR exhibited high crystallinity without impurity, characteristic of the typical MWW, MFI, and MOR structures, respectively [Figure 1A]. Re-Ti-MWW showed a similar XRD pattern as that of Ti-MWW, except for the differences in the low-angle region. Two characteristic diffraction peaks at 2θ = 3.5° and 6.7° attributed to the (001) and (002) crystal planes of layered MWW structure, respectively, appeared in the XRD pattern of Re-Ti-MWW due to the structural change from 3D Ti-MWW to 2D layered Re-Ti-MWW with the assistance of PI [Scheme 1]. The interlayer Si-O-Si linkages were broken in this process, allowing the PI molecules to be inserted between the MWW layers[15]. The presence of PI molecules in Re-Ti-MWW was further confirmed by the TG analysis and[13] C MAS NMR spectrum [Supplementary Figure 1]. Ti-MWW and Re-Ti-MWW had similar nanosheet morphology with a thickness of ~50 nm [Figure 1B (a) and (b)]. TS-1 showed nanoparticle morphology with a diameter of ~ 100 nm [Figure 1B (c)], while Ti-MOR showed irregular crystals on the micrometer scale [Figure 1B (d)]. All the four titanosilicates showed distinct absorption peaks at 210-220 nm attributed to tetrahedrally coordinated Ti species in UV-vis spectra [Figure 1C]. A shoulder peak at 285 nm was observed in the
Figure 1. (A) XRD patterns; (B) SEM images; (C) UV-vis spectra; and (D) N2 adsorption-desorption isotherms at 77 K of (a) Ti-MWW, (b) Re-Ti-MWW, (c) TS-1, and (d) Ti-MOR. XRD: X-ray powder diffractometer; SEM: scanning electron microscope; UV-vis: ultraviolet-visible.
Scheme 1. PI-assisted structural rearrangement of Ti-MWW to Re-Ti-MWW. PI: Piperidine.
Catalytic performance of different titanosilicates in AAL epoxidation
The epoxidation activity of four different zeolites was evaluated in the AAL epoxidation using MeCN as the solvent [Table 1]. Re-Ti-MWW displayed higher AAL conversion of 56.9% and H2O2 utilization efficiency of 97.1% compared to Ti-MWW (34.7% and 88.2%, respectively). TS-1 and Ti-MOR showed significantly lower catalytic activity, with AAL conversion of 8.7% and 2.0%, respectively. All catalysts showed high GLY selectivity of > 97%. Considering that these titanosilicates contain different Ti contents, their catalytic activities were further compared by turnover frequency (TOF). The TOF value of Ti-MWW (1,680) was much higher than those of TS-1 (380) and Ti-MOR (94). The TOF value of Re-Ti-MWW was elevated to 2,754 after the PI-assisted 3D-2D structural transformation of Ti-MWW. Ti-MOR exhibited the lowest catalytic activity for the AAL epoxidation. The poor activity of Ti-MOR has also been reported in the epoxidation of other olefins[16], suggesting that Ti-MOR is not suitable for olefin epoxidation, although it exhibits excellent catalytic activity in aldehydes and ketones ammonia oxidation reactions[18]. The lower activity of medium-pore TS-1 compared to Ti-MWW was probably ascribed to the poor diffusion. Methanol was reported to be the preferred solvent for TS-1 in alkene epoxidation reactions, so the usage of MeCN solvent may also induce the lower activity of TS-1[17].
Catalytic results of four titanosilicates in AAL epoxidationa
| Catalyst | Si/Tib | AAL conv. (%) | GLY sel. (%) | H2O2(%) | TOFc | D/r2 | |
| conv. | eff. | (10-7 s-1)d | |||||
| Ti-MWW | 39 | 34.7 | 99.2 | 39.3 | 88.2 | 1,680 | 20.1 |
| Re-Ti-MWW | 39 | 56.9 | 99.4 | 58.6 | 97.1 | 2,754 | 466.0 |
| TS-1 | 35 | 8.7 | 97.9 | 10.5 | 82.9 | 380 | 3.2 |
| Ti-MOR | 38 | 2.0 | 99.3 | 4.1 | 48.8 | 94 | 6.8 |
Effects of solvent on AAL epoxidation
As described above, the catalytic performance was first compared in MeCN solvent, but different titanosilicate catalysts may have distinct solvent effects[15]. Thus, the epoxidation activity of four zeolites was further evaluated in various solvents [Table 2]. For Ti-MWW zeolite, the AAL conversion of 34.7% in MeCN was higher than that in other protic solvents, suggesting that the most suitable solvent was MeCN, consistent with the previous report[13]. Meanwhile, the GLY selectivity of 99.2% in MeCN was also higher than those in protic solvents, because hydrolysis and alcoholysis easily occur in water and methanol solvents, respectively. For hydrophobic TS-1, the preferred solvent effect was methanol, although the activity of the TS-1 catalyst remained poor in methanol compared to Ti-MWW. The catalytic activity of
Catalytic results of AAL epoxidation over titanosilicates in various solventsa
| Catalyst | Solvent | AAL conv. (%) | GLY sel. (%) | H2O2 (%) | |
| conv. | eff. | ||||
| Ti-MWW | H2O | 30.5 | 96.8 | 32.8 | 92.9 |
| MeCN | 34.7 | 99.2 | 39.3 | 88.2 | |
| MeOH | 13.7 | 90.4 | 22.8 | 60.1 | |
| t-BuOH | 19.6 | 98.5 | 22.7 | 86.3 | |
| Re-Ti-MWW | H2O | 98.1 | 99.1 | 98.5 | 99.5 |
| MeCN | 56.9 | 99.4 | 58.6 | 97.1 | |
| MeOH | 67.4 | 95.1 | 72.1 | 93.5 | |
| t-BuOH | 42.5 | 99.2 | 48.3 | 87.9 | |
| TS-1 | H2O | 10.3 | 95.4 | 13.4 | 76.9 |
| MeCN | 8.7 | 97.9 | 10.5 | 82.9 | |
| MeOH | 14.5 | 88.4 | 19.4 | 74.7 | |
| t-BuOH | 6.3 | 97.1 | 8.7 | 72.4 | |
| Ti-MOR | H2O | 2.3 | 99.5 | 4.7 | 48.9 |
| MeCN | 2.0 | 99.3 | 4.1 | 48.8 | |
| MeOH | 1.7 | 99.1 | 3.4 | 50.0 | |
| t-BuOH | 1.9 | 99.4 | 4.3 | 44.2 | |
The dependence of AAL conversion and GLY selectivity on reaction time between Ti-MWW and
Figure 2. (A) AAL conversion and (B) GLY selectivity of AAL epoxidation with different reaction times over Ti-MWW and Re-Ti-MWW in solvent H2O and MeCN. Reaction conditions: catalyst, 0.03 g; allyl alcohol, 30 mmol; H2O2 (30 wt%), 30 mmol; solvent, 5 mL; temperature, 313 K; time, 5-120 min. The labels in this figure represent “sample name-solvent”. AAL: Allyl alcohol; GLY: glycidol.
The transformation of some tetrahedrally coordinated Ti species into open-site hexa-coordinated Ti species during PI rearrangement treatment was considered as the main reason for the enhanced activity of
Figure 3. (A) Adsorption isotherms and (B) relative adsorption uptake of AAL over four titanosilicates at 313 K; (C) H2O adsorption isotherms and (D) contact angle test of (a) Ti-MWW, (b) Re-Ti-MWW, (c) TS-1, and (d) Ti-MOR. AAL: Allyl alcohol.
Reaction kinetics of AAL epoxidation over Ti-MWW and Re-Ti-MWW
The epoxidation process catalyzed by the titanosilicates/H2O2 system proceeds in two steps. The first step is the activation of H2O2 on the Ti activity centers to generate Ti-Oα-Oβ-H intermediates [Scheme 2][37], which is the rate-determining step of the entire epoxidation process. In the second step, the more electrophilic Oα in the intermediate interacts with the C=C in the olefins to realize the transfer of Oα, producing the epoxides. Therefore, the efficient generation of intermediate Ti-OOH is the key to the improvement of catalytic activity. The ability of Ti-OOH formation was compared between Ti-MWW and Re-Ti-MWW in different solvents. Figure 4A and B showed the relationship between the initial epoxidation rate and H2O2 concentration. A similar variation trend was observed for Ti-MWW and Re-Ti-MWW in both H2O and MeCN solvents. The epoxidation rate increased with increasing H2O2 concentration at lower H2O2 concentration, indicating that
Figure 4. Dependence of AAL epoxidation rate on (A) H2O2 concentration and (B) over (a) Ti-MWW and (b) Re-Ti-MWW; H2O2 concentration and initial reaction rate (C) and (D) in H2O and MeCN. Reaction conditions: catalyst, 0.03 g; allyl alcohol, 30 mmol; H2O or MeCN, 5 mL; temperature, 313 K. AAL: Allyl alcohol.
Scheme 2. Ti-Oα-Oβ-H intermediates generated by the activation of H2O2.
Continuous epoxidation reaction of AAL over Re-Ti-MWW in H2O solvent
Effects of reaction conditions
The continuous liquid-phase AAL epoxidation catalyzed by Re-Ti-MWW in H2O solvent was carried out in a slurry bed reactor. The effects of reaction temperature, weight hourly space velocity (WHSV) of H2O2, AAL/H2O2 molar ratio, catalyst amount, and stirring speed on the performance of AAL epoxidation were investigated in detail. The effect of reaction temperature on the catalytic performance of Re-Ti-MWW in continuous AAL epoxidation reaction was shown in Figure 5A. The H2O2 conversion improved from 96.5% to almost 100% when the reaction temperature increased from 303 to 313 K, although H2O2 effective utilization and GLY selectivity were kept stable at 92.5% and 96.8%, respectively. The effective utilization of H2O2 and GLY selectivity dropped as the reaction temperature was further increased to 323 K. However, the H2O2 conversion remained constant. Although increasing the reaction temperature favored the epoxidation reaction, the ineffective decomposition of H2O2 and the pore-opening reaction of GLY were also enhanced. Thus, the optimum initial operating temperature for the continuous liquid-phase AAL epoxidation was set at 313 K.
Figure 5. (A) Effects of temperature, (B) WHSV of H2O2, and (C) AAL/H2O2 molar ratio on the epoxidation of AAL over Re-Ti-MWW. Reaction conditions: catalyst, 1 g; temperature 313 K; AAL/H2O2 molar ratio, 1.5 (A and B); H2O/AAL mass ratio, 4; WHSV(H2O2) =
The higher WHSV of H2O2 could increase the GLY concentration in the reaction mixture under the condition that H2O2 is completely consumed. With the WHSV of H2O2 setting at 0.3 h-1, the H2O2 conversion, H2O2 effective utilization, and GLY selectivity were 99.4%, 93.6%, and 97.2%, respectively [Figure 5B]. Increasing the WHSV of H2O2 to 0.4 h-1, the H2O2 conversion was not changed while the H2O2 effective utilization and GLY selectivity slightly decreased. When the WHSV of H2O2 was further increased to 0.5 h-1, the H2O2 effective utilization and GLY selectivity declined to 85.2% and 92.5%, respectively. Higher WHSV of H2O2 induced higher H2O2 concentration in the reaction solution, which increased the acidity and then aroused inefficient decomposition of H2O2 and ring-opening of GLY. Hence, the preferred WHSV of H2O2 was determined to be 0.4 h-1.
Although the theoretical AAL/H2O2 ratio is 1 in the epoxidation of AAL with H2O2 as the oxidant, the AAL/H2O2 molar ratio should be greater than 1 in the actual production process to consume all the H2O2 in the system for safety. With the AAL/H2O2 molar ratio of 1, the H2O2 conversion was only 97.1% [Figure 5C]. The H2O2 conversion reached 99.3% when the molar ratio of AAL/H2O2 was raised to 1.5. Further increasing the AAL/H2O2 ratio hardly changed the H2O2 conversion. Thus, the AAL/H2O2 ratio of 1.5 was enough for the complete consumption of H2O2.
The effect of catalyst amount was also investigated [Figure 6A]. Increasing the catalyst amount favored the conversion of H2O2, while the effective utilization of H2O2 and GLY selectivity were decreased. It is conceivable that increasing the catalyst amount raised the content of acid centers, which intensified the ineffective decomposition of H2O2 and ring-opening of GLY. The catalyst amount of 1 g was enough because the complete conversion of H2O2 can be realized. By changing the stirring speed, the influence of external diffusion can be eliminated. In Figure 6B, although the increase of stirring speed increased the H2O2 conversion, the ineffective decomposition of H2O2 was also enhanced. Therefore, 500 rpm was chosen as the optimal stirring speed.
Figure 6. Effects of (A) catalyst amounts and (B) stirring speed on the epoxidation of AAL over Re-Ti-MWW. Reaction conditions: catalyst, 1 g (for Figure 6B); temperature, 313 K; AAL/H2O2 molar ratio, 1.5; H2O/AAL mass ratio, 4; WHSV(H2O2) = 0.4 h-1; 500 rpm (for Figure 6A). The data were the average values at 45 h after the reaction reached a steady state. AAL: Allyl alcohol; WHSV: weight hourly space velocity.
Evaluation of catalyst lifetime
The catalytic performance of Re-Ti-MWW in continuous AAL epoxidation using water and acetonitrile solvent was compared [Figure 7]. The lifetime of Re-Ti-MWW in water solvent reached 121 h, with the average H2O2 conversion, H2O2 effective utilization, GLY selectivity, and GLY yield of 98.1%, 91.1%, 96.3%, and 86.0%, respectively. The H2O2 conversion was maintained at 99% at 313 K for 30 h. After that, the H2O2 conversion started to decrease and the temperature was increased to maintain a high H2O2 conversion
Figure 7. The lifetime of Re-Ti-MWW in the epoxidation of AAL. Reaction conditions: catalyst, 1 g; temperature, 313-323 K; AAL/H2O2 molar ratio, 1.5; solvent/AAL mass ratio, 4; WHSV(H2O2) = 0.4 h-1; 500 rpm. AAL: Allyl alcohol; WHSV: weight hourly space velocity.
As shown in Figure 8A, the lifetime increased to 163 h when 5 ppm of (NH4)2CO3 was added to the reaction feedstock. The GLY selectivity increased from 96.3% to 97.3%. However, introducing the alkaline species in the middle stage of the reaction was less effective [Figure 8B], indicating that the ring-opening of GLY reaction should be prohibited in the early stage, because the by-product glycerol was hardly removed once they are formed.
Figure 8. Effect of ammonia (A) before and (B) after addition on epoxidation of AAL. Reaction conditions: catalyst, 1 g; (NH4)2CO3 amounts, 5 ppm; temperature, 313-323 K; AAL/H2O2 molar ratio, 1.5; H2O/AAL mass ratio, 4; WHSV(H2O2) = 0.4 h-1; 500 rpm. AAL: Allyl alcohol; WHSV: weight hourly space velocity.
CONCLUSIONS
Re-Ti-MWW catalyst with higher hydrophilicity was obtained by PI rearrangement treatment and showed higher catalytic activity in AAL epoxidation reaction than Ti-MWW. High relative diffusion rates of AAL and the formation of more active open-site hexa-coordinated Ti species resulted in increased catalytic activity in AAL epoxidation reaction. Meanwhile, the most suitable solvent was changed from MeCN for
DECLARATIONS
Authors’ contributions
Conception and design of the study: Wu P, Xu H
Data collection and analysis: Gong X
Sample preparation: Tuo J, Wang J, Li X, Zhai C
Paper writing and reviewing: Gong X, Xu H, Wu P
Availability of data and materials
Supporting Information is available from the corresponding author upon reasonable request.
Financial support and sponsorship
We gratefully acknowledge the financial support from the National Key R&D Program of China (No. 2021YFA1501401, No. 2023YFB3810602) and the National Natural Science Foundation of China (No. 22222201).
Conflicts of interest
All authors declared that there are no conflicts of interest.
Ethical approval and consent to participate
Not applicable.
Consent for publication
Not applicable.
Copyright
© The Author(s) 2024.
Supplementary Materials
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Gong, X.; Tuo, J.; Wang, J.; Li, X.; Zhai, C.; Xu, H.; Wu, P. Hydrophilic Ti-MWW for catalyzing epoxidation of allyl alcohol. Chem. Synth. 2024, 4, 14. http://dx.doi.org/10.20517/cs.2023.59
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