Insight into the role of meso-Y zeolites in CsPMo/meso-Y composites on the selective oxidation of sulfides enhancement

doi:10.21203/rs.3.rs-4823244/v1

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Insight into the role of meso-Y zeolites in CsPMo/meso-Y composites on the selective oxidation of sulfides enhancement

https://doi.org/10.21203/rs.3.rs-4823244/v1

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Polyoxometalates (POMs), renowned for their excellent catalytic activity, are widely used in oxidation reactions. Rational regulation of metal ion valence state of POMs is of great significance for the design and construction of highly active catalyst. In this work, we utilized mesoporous Y zeolite (meso-Y) as a host to load and disperse cesium phosphomolybdate (CsPMo) for selective oxidation of thioethers. The as-prepared CsPMo/meso-Y featured superior catalytic activity and recyclability. The electronic structures of the CsPMo/meso-Y were investigated by XPS and NMR spectra. The results indicated that embedding CsPMo into meso-Y caused electron transfer between CsPMo and meso-Y. Meanwhile, meso-Y could provide H⁺ due to its abundant Bronsted acid sites. The simultaneous appearance of electron and H⁺ facilitated the formation of Mo^V, resulting in a higher oxidation of thioethers activity for the CsPMo/meso-Y. Radical scavenger experiments and Raman analysis indicated that peroxo-metal species derived from CsPMo and oxidizing agent tert-butyl hydroperoxide (TBHP) were the real catalyst. Mo^V is more conducive to the formation of peroxo-metal species, causing the higher activity. This study provides a new insight into the role of meso-Y in CsPMo/meso-Y and a novel clue to regulate the valence states of metal ions of POMs to enhance catalytic performance of the polyoxometalate based catalysts.

Physical sciences/Materials science/Materials for energy and catalysis/Porous materials

Physical sciences/Chemistry/Catalysis/Heterogeneous catalysis

Polyoxometalates (POMs), a class of anionic metal-oxygen clusters, are composed of oxygen and early transition metal elements (Mo, W, V, Nb, and Ta) in the highest oxidation¹. Based on their diverse composition and structure, high acidity and reversible redox activity, POMs are widely applied as acid and oxidation catalysts^2–4. Keggin anions show high oxidation activity because their lowest unoccupied molecular orbitals (LUMOs) are nominally nonbonding orbitals for MO₆ octahedra⁵. In particular, phosphomolybdic acid (H₃PMo₁₂O₄₀) has been used as oxidation catalyst in various organic reactions⁶. There are four types of oxygen in the H₃PMo₁₂O₄₀ structure: (1) tetrahedral oxygen linked with P (O_a); (2) bridging oxygen connected with different trimetallic clusters (O_b); (3) bridging oxygen in the same trimetallic cluster (O_c); (4) terminal oxygen (O_d). For the H₃PMo₁₂O₄₀, protonation of some bridging oxygens, which involve simultaneous addition of electrons and protons, can result in forming mix-valence species (heteropoly blues), which show more excellent catalytic performances^{5, 7}. Hence, it is worth trying to tune the valence of metal ions of H₃PMo₁₂O₄₀ to improve the catalytic property by tuning electron population and extent of protonation of microenvironment around Keggin anions.

However, POMs are usually soluble and difficult to be separated and recycled in polar solvents, and have a low specific surface area in nonpolar solvents (< 10 m²·g^− 1), causing a performance degradation in catalytic reactions⁸. Loading POMs on different types of porous materials could resolve the problems. Recently, a series of materials, such as metal-organic frameworks (MOFs)^{7, 9, 10}, carbon materials^{11, 12}, mesoporous silica^13–16, and zeolites^{8, 17–19}have been used as supports to realize recycling and reusability.

Among numerous supports, zeolites, renowned for regular pore structure, large specific surface area, tunable acidities, and outstanding thermal/chemical stability, have been proven to be ideal supports to disperse and stabilize active functional materials under rigorous reaction conditions^20–25. More importantly, the interactions between guests and the zeolites could tune their electronic structure, affording unprecedented performance to either original zeolite or pristine guest^26–28. For POMs, the presence of H⁺ can facilitate the formation of mix-valence species⁵. Zeolites may provide H⁺ for POMs due to their abundant Bronsted acid sites, which is likely conducive to enhance catalytic performance. However, the pore size of microporous zeolites is smaller (< 1 nm) than that of POMs so that it’s difficult for POMs to enter the zeolite channels. Using hierarchical zeolites containing both microporosity and meso/macroporosity as support can solve the problem. The POMs/hierarchical zeolites composites could be easily separated, recovered, and reused. However, POMs would leach out easily from zeolites due to their good solubility in polar solvents, causing their catalytic activity decrease. In comparison with the parent POMs, the corresponding POM salts with alkali metal cations such as Cs⁺ and K⁺ are insoluble in polar solvents, which are beneficial to their recyclability^{29, 30}. For example, potassium tungstophosphate (KPW) was immobilized on ZSM-5 zeolites with various Si/Al ratios to improve the activity and recyclability in ethanol dehydration and nicosulfuron removal³¹. And it was reported that a stable heteropolyacid (HPA)/zeolite composite was developed by immobilizing Cs exchanged 12-tungstophosphoric acid on high-silica mesoporous Y, which showed good reusability and catalytic performance in esterification for ethyl lactate (EL) synthesis⁸. However, there remains a lack of in-depth understanding of the role of zeolites on improving catalytic performance of POMs/zeolites composites.

Herein, mesoporous Y zeolite (meso-Y) was chosen as support to load CsPMo to prepare a series of CsPMo/meso-Y zeolite composites (Scheme 1). The obtained CsPMo/meso-Y showed superior catalytic capacity and excellent recyclability for oxidation of thioethers reactions. To our knowledge, investigations of oxidation of thioethers reactions on CsPMo/meso-Y, are rare. Especially, the mechanism that zeolites improve the catalytic performance of POMs is not clear. This work reveals that there are strong interactions and electron transfer between CsPMo and meso-Y. More significantly, meso-Y can regulate the valence of Mo of CsPMo to promote the generation of Mo^V via offering H⁺, resulting in an improvement in catalytic activity. This work provides a further insight into the influence of zeolites on POMs as well as a feasible method to rationally regulate valence of metal ions of POMs to improve their performances.

Characterization of CsPMo/meso-Y

The powder X-ray diffraction (XRD) was carried out to investigate the structures of CsPMo/meso-Y with different CsPMo loadings as shown in Fig. 1a. The diffraction peaks of CsPMo/meso-Y coincided exactly with that of meso-Y, indicating that the incorporation of CsPMo doesn’t affect the structure of meso-Y³². Moreover, the diffraction peaks of CsPMo were not observed in the XRD patterns of CsPMo/meso-Y, indicating that CsPMo was uniformly high-dispersed in the meso-Y³³. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images in Supplementary Figs. 1 and 2 show that both meso-Y and CsPMo/meso-Y exhibit blocky morphology without obvious difference, indicating that the structure and morphology of meso-Y don’t change after the loading of CsPMo, which is in agreement with the result of XRD analysis. The Fourier-transform infrared (FT-IR) spectra of CsPMo/meso-Y with different CsPMo loadings are shown in Fig. 1b, which show typical infrared bands corresponding to Y zeolite. Besides, two extra characteristic peaks are detected at 970 and 911 cm^− 1, which are assigned to the stretching vibrations of Mo = O and Mo-O_b-Mo of CsPMo, respectively³⁴. This result indicates that CsPMo is successfully loaded on meso-Y³⁵.

N₂ adsorption-desorption measurements were conducted on meso-Y and CsPMo/meso-Y, which are shown in Supplementary Fig. 3 and Supplementary Table 1. In comparison to the original meso-Y, the N₂ adsorption capacity, specific surface area, pore volume and average pore diameter of CsPMo/meso-Y decrease. Among them, the specific surface area of 7.5% CsPMo/meso-Y decreases from 662 m²/g to 558 m²/g, the pore volume decreases from 0.20 cm³/g to 0.13 cm³/g and the average pore diameter decreases from 4.94 nm to 2.92 nm, which also demonstrate that CsPMo is successfully loaded into the pores of the meso-Y³⁶. It is worth noting that CsPMo/meso-Y maintains the abundant void space even after loading CsPMo, which can be conducive to the adsorption of thioether into meso-Y channel to improve the catalytic activity for oxidation reaction^{26, 37}. Supplementary Fig. 4 shows the energy-dispersive X-ray spectroscopy (EDS) images of 7.5% CsPMo/meso-Y, which manifest the uniform dispersion of Cs, P, Mo, Si and Al elements in CsPMo/meso-Y. In other words, CsPMo is well distributed within meso-Y. Inductively coupled plasma-optical emission spectrometry (ICP-OES) was used to determine the Mo content in the CsPMo/meso-Y catalysts (Supplementary Table 1). By calculation, the actual loadings of CsPMo are 3.3%, 4.6%, 6.0%, 7.5% and 9.3%, respectively, which increase with the incorporation of CsPMo. The results further confirm that CsPMo is successfully loaded on the meso-Y.

The electronic structure of the CsPMo/meso-Y was further investigated by X-ray photoelectron spectroscopy (XPS) analysis. The Mo 3d spectrum of CsPMo (Fig. 2a) shows two peaks at 233.0 and 236.1 eV, which correspond to Mo^VI 3d_5/2 and Mo^VI 3d_3/2, respectively. Compared with CsPMo, two additional peaks at ca.232.5 and 235.4 eV are observed in the spectra of CsPMo/meso-Y, which can be attributed to Mo^V 3d_5/2 and Mo^V 3d_3/2, respectively

$$\:(PM{o}_{\text{12}}^{\text{VI}}{O}_{40}{)}^{3-}+\text{pe}+\text{q}{\text{H}}^{+}\to\:{H}_{q}(PM{o}_{12-p}^{VI}M{o}_{p}^{V}{O}_{40}{)}^{(q-p-3)}$$

(Fig. 2b–f)³⁸. The results clearly demonstrate that Mo^V formed in the CsPMo/meso-Y, which can be further confirmed by the phenomenon that the products changed from yellow (CsPMo) to green (CsPMo/meso-Y) (Supplementary Fig. 5). It is worth noting that the peaks of Mo^VI 3d_5/2, Mo^VI 3d_3/2 and O 1s (Fig. 3a) in the 7.5% CsPMo/meso-Y shift towards higher binding energies in contrast to CsPMo. Furthermore, compared with meso-Y, the binding energies of O 1s and Si 2p of 7.5% CsPMo/meso-Y decrease (Fig. 3a, b). These results indicate that electrons transfer from CsPMo to meso-Y, which demonstrates that the interactions formed between CsPMo and meso-Y⁷. The formation of Mo^V is likely to be caused by the incorporation of CsPMo into meso-Y. It is well-known that the presence of electrons and H⁺ at the same time is conducive to the formation of Mo^V (Eq. (1))^{5, 39}. On the one hand, electron transfer occured between CsPMo and meso-Y during the preparation of the CsPMo/meso-Y. On the other hand, meso-Y could provide a lot of H⁺ due to its abundant Bronsted acid sites. In other words, the incorporation of CsPMo into meso-Y can offer both electrons and H⁺, which facilitate the formation of Mo^V. Above data demonstrate that meso-Y with abundant Bronsted acid sites is an excellent support which can regulate the valence of Mo of CsPMo.

To further investigate the interaction between CsPMo and meso-Y, we performed ³¹P solid state nuclear magnetic resonance (³¹P NMR) analyses of CsPMo and CsPMo/meso-Y. As seen in Fig. 4, a typical resonance at -6.35 ppm is observed for pure CsPMo, which can be attributed to the P atom

of the CsPMo Keggin structure. For the CsPMo/meso-Y, the resonance peak is nearly the same with that of CsPMo, suggesting that the Keggin structure of CsPMo was well-preserved. It is worth noting that a slight shift of P signal to downfield is observed after the incorporation of CsPMo into meso-Y, proving that there could be strong interactions between CsPMo and meso-Y, resulting in a lower electron density about the P atoms⁷. This feature further confirms the XPS results that there are electrons transfer between CsPMo and meso-Y.

Catalytic oxidation of thioether

The activities of selective oxidation of sulfides over CsPMo/meso-Y were tested with methyl p-tolyl sulfide as a model substrate and tert-butyl hydroperoxide (TBHP) as an oxidant (Table 1). In order to explore the optimal conditions for the reaction, the effects of CsPMo loadings, solvent types, catalyst dosages, reaction temperature and molar ratio of TBHP/substrate (O/S) on the catalytic performance were investigated.

The conversion of methyl p-tolyl sulfide by meso-Y alone was just 32.34% (Table 1, entry 7), while the conversion was 29.93% without catalyst (Table 1, entry 8), suggesting that meso-Y is not responsible for the reaction. Pure CsPMo also showed relatively low conversion (80.64%), which could be attributed to the insufficient exposure of active sites. The conversion of the prepared composites (CsPMo/meso-Y) was increased to more than 96% within 30 min (Table 1, entries 1–5), manifesting the higher activity for oxidation of thioether after embedding CsPMo into meso-Y. This might be attributed to the formation of mixed-valence species ((PMo^{VI, V}O₄₀)^x−), which has proven to be conducive to improve catalytic activity^{40, 41}. Further, the effect of CsPMo loading amount on the catalytic performance for oxidation of sulfides was

Table 1| Activities of different catalysts towards the oxidation of methyl p-tolyl sulfide^a.

Entry	Catal.	Catal. (mg)	O/S^b	Con. (%)	Sel.^c (%)
1	3.3% CsPMo/meso-Y	10	1	96.81	98.74
2	4.6% CsPMo/meso-Y	10	1	97.29	97.95
3	6.0% CsPMo/meso-Y	10	1	98.2	98.05
4	7.5% CsPMo/meso-Y	10	1	99.14	98.31
5	9.3% CsPMo/meso-Y	10	1	98.62	98.56
6	CsPMo	0.8	1	80.64	98.79
7	meso-Y	9.2	1	32.34	98.32
8	Blank	0	1	29.93	98.01

^aReaction conditions: 0.5 mmol substrate, 1 mL ethanol, 0.5 mmol TBHP, 60 ^oC, 30 min.

^bO/S = the molar ratio of oxidant to substrate.

^cThe selectivity of sulfoxide, the byproduct is sulphone.

investigated by increasing the CsPMo loadings from 3.3–9.3% (Table 1, entries 1–5). The conversion of methyl p-tolyl sulfide rose as the CsPMo loadings increased. While the conversion decreased when the loadings of CsPMo exceeded 7.5%. As seen in Table 1, 7.5% CsPMo/meso-Y showed the highest activity (99.14%) due to its highest Mo^V content, which can be confirmed by XPS (Fig. 2b–f). Figure 5a shows the solid-state UV-visible absorption spectra, a peak at ca.700 nm is observed, which corresponds to heteropoly blue⁴². And 7.5% CsPMo/meso-Y shows more significant absorption, which indicates that 7.5% CsPMo/meso-Y has the highest Mo^V content^{42, 43}. This result is consistent with the results of XPS and the fact that 7.5% CsPMo/meso-Y shows a darker green (Supplementary Fig. 5). Meanwhile, according to the molar ratio of Mo^VI/Mo^V in Supplementary Table 2, 7.5% CsPMo/meso-Y has the highest Mo^V content. These results implied that Mo^V played a crucial role in oxidation of methyl p-tolyl sulfide. Additionally, the cyclic voltammetry (CV) further demonstrated the oxidative capability of 7.5% CsPMo/meso-Y was increased compared with either meso-Y or CsPMo (Fig. 5b), which may due to the higher active area after the incorporation of CsPMo into meso-Y, causing the higher activity for selective oxidation of thioether⁴¹.

As seen in Fig. 6, conversion and selectivity could be affected by various solvents. When ethanol was used as solvent, 7.5% CsPMo/meso-Y showed the highest conversion (99.14%). Interestingly, the conversion with various solvents followed the order of ethanol > n-propanol > n-butanol > n-pentanol > cyclohexane, which could be related to the polarity of the solvents. Polarity can be expressed with dielectric constant ε, polarity/polarizability index π* and Dimroth-Reichardt’s polarity parameter E_T(30) (Supplementary Table 3)^44–48. It can be seen that the more polar the solvent is, the easier it is to provide protons. These protons originating from solvent contribute to facilitating the oxidation reaction according to Eq. (2), where [HPA]_ox and [HPA]_red represent the oxidized and reduced forms of the heteropolyanion, respectively⁵. Similarly, meso-Y could also contribute to this oxidation process by supplying H⁺ for the process. While the relatively low conversion (96.33%) was obtained with methanol as solvent, whose polarity is highest. This may be due to the low solubility of methyl p-tolyl sulfide in methanol.

$$\:{\left[HPA\right]}_{ox}+substrate+{iH}^{+}\rightleftarrows\:{H}_{i}{\left[HPA\right]}_{red}+oxidized\:substrate\:\:\:\:\:\:\:\:$$

The dosage of catalysts, reaction temperature and the molar ratio of TBHP/substrate (O/S) also have influences on the catalytic performance of the reaction (Fig. 7a–c). The results revea-

led that the optimum amount of catalyst is 10 mg, which led to a conversion (99.14%) and selectivity (98.31%) of thioether within 30 min (Fig. 7a). The conversion of methyl p-tolyl sulfide increased as the reaction temperature rose to 60 ^oC; when the temperature reached 70 ^oC, the conversion of thioether decreased slightly. Therefore, the optimum temperature for the reaction is 60 ^oC. In addition, the exorbitant O/S could cause the selectivity decrease, which is due to the fact that excess oxidant leads to further oxidation of methyl p-tolyl sulfoxide to methyl p-tolyl sulfone⁴⁹. Based on the above results, under the optimal reaction conditions, methyl p-tolyl sulfide can be converted to methyl p-tolyl sulfoxide within 30 minutes (Fig. 7d).

Due to the excellent results obtained above, a series of sulfides were selected as substrates to investigate the catalytic activity of the 7.5% CsPMo/meso-Y (Supplementary Table 4). The results show that the conversions of these substrates are all above 98% within 30 min, which clearly demonstrates that 7.5% CsPMo/meso-Y shows outstanding catalytic capability in the oxidation of sulfides.

In addition, the cycling stability of the 7.5% CsPMo/meso-Y catalyst was investigated. The used catalyst was centrifuged and washed three times with ethanol, and dried at 60 ^oC. As shown in Fig. 8a, the conversion and selectivity of the reaction don’t decrease significantly after three cycles (the conversion of methyl p-tolyl sulfide is 93.42% and the selectivity of methyl p-tolyl sulfoxide is 99.59% in the third cycle), indicating that the 7.5% CsPMo/meso-Y catalyst has excellent cycling stability. The XRD, FT-IR and EDS spectra of recovered 7.5% CsPMo/meso-Y after 3 cycles are consistent with those of fresh 7.5% CsPMo/meso-Y (Supplementary Figs. 6 and 7), which further proves the excellent stability and reusability of 7.5% CsPMo/meso-Y under reaction conditions.

Furthermore, we also investigated the oxidation reaction mechanism of methyl p-tolyl sulfide by free radical trapping experiments and Raman (Fig. 8b and Supplementary Fig. 8). It has been found that the introduction of scavengers, including 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), isopropanol (IPA), p-benzoquinone (PBQ) and diphenylamine (Ph₂NH), has little effect on the conversion of thioether, suggesting that there is no involvement of free radicals in this catalytic process^{50, 51}. Therefore, based on previous literatures, we speculated that the peroxo-metal group, which ariose due to the interaction between POM and TBHP, played a key role in the catalytic oxidation reaction^{52, 53}. To confirm the inference, Raman spectra of 7.5% CsPMo/meso-Y were measured before and after use (Supplementary Fig. 8). Indeed, the difference of the peaks at 886 cm^− 1 was observed after catalysis, assigned to the -O-O- vibrations, indicating the formation of peroxo-metal species^{54, 55}. The mechanism for the catalytic oxidation of sulfides was proposed as shown in Fig. 8c, the active peroxo-molybdenum derived from 7.5% CsPMo/meso-Y and TBHP catalyzed the S atoms of the sulfides to obtain the corresponding sulfoxides and sulfones. Compared with CsPMo, the binding energy of mixed-valence species ((PMo^{VI, V}O₄₀)^x−) with TBHP is higher, which is conducive to the formation of peroxo-metal species, causing a higher sulfide oxidation performance⁷.

In conclusion, CsPMo/meso-Y was obtained by ion exchange and impregnation method. Incorporation of CsPMo into meso-Y not only improved the catalytic activity for oxidation of sulfide, but also increased the cycling stability. The superior performance was attributed to the more exposed active sites and higher active area. More importantly, electron and H⁺ generated around Mo^VI due to the incorporation of CsPMo into meso-Y, which promoted the formation of Mo^V, resulting in higher activity. This work provides a powerful tool to regulate the metal ion valence state of POMs by loading and high dispersion of POMs within zeolite.

Materials and chemicals

All chemicals were commercially obtained without purification. Caesium carbonate (Cs₂CO₃, 99%), phosphomolybdic acid hydrate (H₃PMo₁₂O₄₀·xH₂O, Mo: 45–63%, denoted as HPMo), methyl phenyl sulfide (99%), 2-chloroethyl ethyl sulfide (97%) and 4-methoxythioanisole (98%) were purchased from Shanghai Aladdin Biochemical Science and Technology Co. Hierarchical mesoporous zeolite Y (meso-Y) was purchased from Tianjin Nanhua Catalysts Co. Methyl p-tolyl sulfide (98%) and diethyl sulfide (≥ 98%) were purchased from Shanghai Macklin Biochemical Science and Technology Co. 3-Chlorothioanisole (99%) was purchased from Shanghai Jiuding Chemical Technology Co. 2-Chlorothioanisole (≥ 98%) and 4-chlorothioanisole (≥ 98%) were purchased from Shanghai Adamasbeta Chemical Reagent Co.

Characterization

Powder X-ray diffraction (PXRD) patterns of the samples were measured by a D/teX Ultra diffractometer with Cu Kα radiation (λ = 1.5418 Å). The FT-IR spectra were tested by a Varian 640 FT-IR spectrometer. Scanning electron microscope images (SEM) were conducted on a cold field-emission scanning electron microscope (S-4800). Transmission electron microscopy (TEM) images were tested on JEOL JSM-6510. The nitrogen adsorption/desorption isotherms and pore size distributions were measured by Kubo-X1000. The energy-dispersive X-ray spectroscopy (EDS) images were conducted on Hitachi SU8020. Inductively coupled plasma-optical emission spectrometry (ICP-OES) was analyzed by Agilent 5110. X-ray photoelectron spectroscopy (XPS) patterns were measured on Thermo ESCALAB 250. ³¹P solid state nuclear magnetic resonance (³¹P NMR) spectra were tested by Bruker AVANCE III 500 HD. The solid-state UV-visible absorption spectra were conducted on PE-Lambda-750. The Raman spectra were measured on HORIBA-LabRAM HR Evolution. The catalytic reaction was analyzed by using a Shimadzu Tech-comp GC-7900 gas chromatograph (GC) with a flame ionization detector equipped with a TM-5 Sil capillary column.

Preparation of the catalysts

Meso-Y supported Cs exchanged HPMo (Cs/meso-Y) was obtained by a simple ion exchange and impregnation method that has been described elsewhere⁸.

Preparation of Cs/meso-Y

Firstly, meso-Y was calcined at 550 ^oC for 2 h. Then, 0.055 g of Cs₂CO₃ was dissolved in 60 mL water and 4 g meso-Y was added. The mixed solution was stirred at room temperature for 2 h, evaporated at 60 ^oC and dried at 100 ^oC for 12 h. Finally, the solid product was calcined at 500 ^oC for 2 h to obtain Cs/meso-Y.

Preparation of CsPMo

Firstly, 1.075 g Cs₂CO₃ was dissolved in 60 mL water to obtain the Cs₂CO₃ solution. Then, 2 g HPMo was dissolved in 30 mL water to obtain the phosphomolybdic acid solution. The Cs₂CO₃ solution was added dropwise to the phosphomolybdic acid solution. The mixed solution was stirred vigorously for 2 h, aged overnight at room temperature and evaporated at 60 ^oC. The obtained solid product was washed five times with deionized water and dried at 60 ^oC overnight to obtain CsPMo.

Preparation of CsPMo/meso-Y

CsPMo/meso-Y was prepareed by impregnation. First of all, 0.4, 0.6, 0.8, 1.0, and 1.2 g of HPMo was dissolved in 30 mL water, respectively, and then 4 g of Cs/meso-Y was added. The mixture was stirred for 2 h at room temperature, sonicated for 40 min, and evaporated at 60 ^oC. After evaporation, the solid products were washed twice with deionized water and dried at 100 ^oC overnight to obtain CsPMo/meso-Y. The prepared materials are denoted as X% CsPMo/meso-Y (X is the mass fraction of CsPMo in the products. The value of X was calculated based on ICP-OES).

Catalytic oxidation of thioether

X% CsPMo/meso-Y was used as the catalyst for the reaction. The substrate (0.5 mmol), catalyst (10 mg), 70% TBHP (0.5 mmol), ethanol (1 mL) and biphenyl (internal standard, 10 mg) were added into a 10 mL glass pressure-resistant tube and stirred at 60 ^oC for 30 min. The conversion of the sulfides and the selectivity of sulfoxides were determined by gas chromatography (GC).

Competing interests

The authors declare no competing interests.

Author contributions

Chang Sun: Writing − original draft, Software, Data curation, Funding acquisition, Investigation, Methodology, Conceptualization. Yutong Han: Writing − original draft, Software, Data curation, Investigation, Methodology, Visualization. Yingzhen Wei: Data curation, Visualization. Zhong Zhang: Funding acquisition, Conceptualization. Xiaohui Li: Funding acquisition, Methodology. Guocheng Liu: Visualization. Xiuli Wang: Writing − review and editing, Funding acquisition, Validation.

Acknowledgements

This work was supported by the NSFC (nos. 22301019, 22271021, 22201021, 21901018, 21971024), the China Postdoctoral Science Foundation funded project (no. 2023-BS-191), the Liao Ning Revitalization Talents Program (XLYC1902011).

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Scheme 1 is available in the Supplementary Files section.

There is NO Competing Interest.

SC1.jpg
Scheme 1| Preparative route for CsPMo/meso-Y.
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Insight into the role of meso-Y zeolites in CsPMo/meso-Y composites on the selective oxidation of sulfides enhancement

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Abstract

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Introduction

Results and Discussion

Characterization of CsPMo/meso-Y

Catalytic oxidation of thioether

Conclusions

Experimental

Materials and chemicals

Characterization

Preparation of the catalysts

Preparation of Cs/meso-Y

Preparation of CsPMo

Preparation of CsPMo/meso-Y

Catalytic oxidation of thioether

Declarations

Competing interests

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Acknowledgements

References

Scheme 1

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Supplementary Files

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