Hybrid Polyoxotungstate/MIL-101 Materials: Synthesis, Characterization, and Catalysis of H₂O₂-Based Alkene Epoxidation

Abstract

Polyoxotungstates [PW(4)O(24)](3-) (PW(4)) and [PW(12)O(40)](3-) (PW(12)) have been inserted into nanocages of the metal organic framework MIL-101. The hybrid materials PW(x)/MIL-101 (x = 4 or 12) containing 5-14 wt % of polyoxotungstate have been obtained and characterized by elemental analysis, N(2) adsorption, FT-IR, Raman, and (31)P NMR MAS spectroscopic techniques. Their catalytic performance was assessed in the selective oxidation of alkenes with aqueous hydrogen peroxide under mild reaction conditions ([H(2)O(2)] = 0.1-0.2 M, 50 degrees C, MeCN). PW(x)/MIL-101 enclosing 5 wt % of polyoxotungstate demonstrated fairly good catalytic activities in the epoxidation of various alkenes (3-carene, limonene, alpha-pinene, cyclohexene, cyclooctene, 1-octene), the turnover frequencies (TOF) and alkene conversions were close to the corresponding parameters achieved with homogeneous PW(x). For the oxidation of substrates with aromatic groups (styrene, cis- and trans-stilbenes), a higher level of olefin conversion was attained using PW(12)/MIL-101. Moreover, confinement of PW(12) within MIL-101 nanocages allowed us to reach higher epoxide selectivities at higher alkene conversions. The hybrid PW(x)/MIL-101 materials were stable to leaching, behaved as true heterogeneous catalysts, were easily recovered by filtration, and reused several times with the maintenance of the catalytic performance.

The coordinatively saturated vanadium MIL-47 as a low leaching heterogeneous catalyst in the oxidation of cyclohexene

“…Moreover, unlike traditional immobilized catalysts 9,10,11 , the active catalytic sites in MOFs are well protected by the coordination bonds which prevents leaching to a higher extent. Although the research in this field is relatively new, MOFs have been studied as catalysts in hydrogenation and oxidation reactions 12,13,14,15,16,17,18 enantioselective reactions 19,20,21 , photocatalysis 22 , carbonyl cyanosilylation 23,24,25 , hydrodesulfurization 26 and esterification 27 .…”

Aerobic Epoxidation of Olefins Catalyzed by the Cobalt‐Based Metal–Organic Framework STA‐12(Co)

“…MOFs usually have high porosity and specific surface areas that make them adequate candidates for catalytic applications both as high-surface-area supports and as intrinsic catalysts. [26,27] MOFs have been used as catalysts for various types of oxidation reactions in the liquid phase, for example, alcohol oxidation, [28] epoxidation, [29][30][31][32] hydrocarbon oxidation, [33][34][35][36] hydroquinone oxidation, [37] the oxidation of organic sulfides, [38] and the oxidation of aromatics. [39] For these oxidation reactions especially, a certain degree of deactivation is frequently observed.…”

Cobalt aluminate nanoparticles supported on MIL-101 structure: catalytic performance investigation

“…In CoAl-1@MIL(Cr), the higher number of catalytic active centers present per cavity of MIL-101(Cr) could result in a more pronounced connement effect. 39,46 In this case, more frequent interactions between the active centers and the substrates will occur which could lead to higher conversion values.…”