Polyoxometalate [γ-SiW10O34(H2O)2]4− on MCM-41 as catalysts for sulfide oxygenation with hydrogen peroxide

• Compared two immobilization protocols: physisorption (I) and chemisortion (II).
• I results in minimal structural degradation but catalyst deactivates upon reuse.
• II results in partial structural degradation but shows no deactivation upon reuse.
• II is applicable to a variety of organic sulfide substrates.

The polyoxometalate (POM) catalyst, [γ-SiW10O34(H2O)2]4−, was introduced into the pores of both as-synthesized (I) and amine functionalized MCM-41 (II). The resultant catalysts were characterized with powder X-ray diffraction, nitrogen sorption, and diffuse-reflectance UV–vis spectroscopy. Both catalysts were tested for reusability through repeated catalytic conversions of methyl phenyl sulfide to methyl phenyl sulfone with hydrogen peroxide. While the physisorbed catalyst (I) exhibits steadily decreasing turnover frequency (TOF), the POM catalyst supported on MCM-41 functionalized with a protonated amine (II) exhibits markedly improved reusability. This chemisorbed catalyst effectively showed no change in TOF between the second (21) and the sixth reactions (22). Additionally, sulfoxidations with catalyst II were investigated with a small set of substrates focusing on compounds including dibenzothiophene, which serves as a model refractory sulfide.

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