Catalytic activity of advanced titanosilicate zeolites in hydrogen peroxide S-oxidation of methyl(phenyl)sulfide

Abstract

Titanium-containing zeolite-based catalysts have been synthesized and investigated as catalysts in methyl (phenyl)sulfide oxidation with hydrogen peroxide. A hierarchical TS-1 prepared by the secondary templating and a layered TS-1 without and with silica and silica-titania pillars have been studied. Conventional TS-1 was a benchmarking material. The study focuses on observation of the different catalytic performance with regard to textural properties; presence and volume of mesopores and different diffusion characteristics. Thus, a deficiency and excess of the oxidizing agent were used in the catalysed reactions and the progress of reaction and selectivity to products were studied. All tested catalysts have shown after 240 min almost total conversion of methyl (phenyl)sulfide with different selectivity (substrate/catalyst mass ratio 10). It was observed that the reactants ratio hydrogen peroxide/ methyl(phenyl)sulfide influences the selectivity to sulfoxide or sulfone over a particular catalyst. In the case of hydrogen peroxide deficiency experiments (H2O2/sulfide = 0.5 mol/mol) the catalysts exhibited different distributions of products. Lamellar catalyst provided 100% selectivity to sulfoxide, the others in range of 90-65% selectivity to sulfoxide; however, the selectivity was independent on the reaction time and substrate conversion. In the case of the excess of the oxidant, except for Ti-pillared TS-1, all the catalysts showed stabile selectivity of 65% towards methyl(phenyl)sulfoxide being independent of the catalyst. The Ti-pillared TS-1 has shown, during the reaction progress, a decrease in the selectivity to sulfoxide from initial 60% to final 20% of sulfoxide at almost total conversion. The only case when higher selectivity to sulfone was achieved was gradual dosing of hydrogen peroxide.