Accessibility enhancement of TS-1-based catalysts for improving the epoxidation of plant oil-derived substrates

Abstract

TS-1-based catalysts with different textural features, namely layered TS-1, pillared TS-1, and Ti-pillared TS-1 as well as mesoporous TS-1, were investigated in the liquid-phase epoxidation of methyl oleate as a model compound for plant oil-derived substrates with hydrogen peroxide at 50 °C. While over the TS-1-based catalysts, except Ti-pillared TS-1, an epoxide selectivity of up to 93% is achieved, layered and pillared TS-1 are the most active (the amounts of methyl oleate converted after 5 h per number of Ti-sites are 4.64 mol mol⁻¹ and 4.68 mol mol⁻¹) with an efficiency for H₂O₂ conversion to the epoxide of 27%. Mesoporous TS-1 and conventional microporous TS-1 exhibit a similar activity (3.64 mol mol⁻¹vs. 3.37 mol mol⁻¹), whereas the mesoporous catalyst most efficiently utilizes H₂O₂ (39% efficiency). The lowest catalytic activity (0.82 mol mol⁻¹), epoxide selectivity as well as H₂O₂ efficiency are observed over Ti-MCM-36, possessing mainly octahedrally coordinated Ti-sites. The results demonstrate the importance of accessibility of Ti-sites at external crystal surfaces within layered and pillared TS-1, significantly increasing the epoxidation activity with respect to the number of Ti-atoms present in the catalysts.