Mesoporous Methyl-Functionalized Titanosilicate Produced by Aerosol Process for the Catalytic Epoxidation of Olefins

Lucia E Manangon-Perugachi,Alvise Vivian,Valentin Smeets,Eric M Gaigneaux,Pierre Eloy,Itika Kainthla,Carmela Aprile,Damien P Debecker

doi:10.3390/catal11020196

Lucia E Manangon-Perugachi, Alvise Vivian + Show 6 more

Open Access

https://doi.org/10.3390/catal11020196

Copy DOI

Abstract

Titanosilicates (Ti-SiO2) are well-known catalysts for the epoxidation of olefins. Isolated Ti inserted in the silica framework in tetrahedral coordination are the active species. Recently, adjusting the hydrophobic/hydrophilic balance of such catalysts’ surfaces has appeared as a promising tool to further boost their performance. However, adjusting the hydrophobic/hydrophilic balance via a one-pot classical sol-gel generally leads to a decrease in the Ti dispersion and/or collapse of the pore network. To overcome this limitation, hydrophobic mesoporous Ti-SiO2 were here synthesized by aerosol-assisted one-pot sol–gel, which allowed the simultaneous control of their Ti loading, degree of methyl-functionalization, and textural properties. Methyl-functionalization was achieved by a partial substitution of tetraethoxy silane (TEOS) by methyltriethoxy silane (MTES) in different ratios. Solid-state 29Si-NMR, FTIR, TGA, and vapor-phase water adsorption showed that methyl moieties were effectively incorporated, conferring a hydrophobic property to the Ti-SiO2 catalysts. ICP-AES, DRUV, XPS, and N2 physisorption demonstrated that Ti dispersion and textural properties were both successfully preserved upon the incorporation of the methyl moieties. In the epoxidation of cyclooctene with tert-butyl hydroperoxide as oxidant, the hydrophobic Ti-SiO2 showed higher catalytic performance than pristine Ti-SiO2 prepared without MTES. In addition to disentangling the positive effect of adjusting the hydrophobic/hydrophilic balance of epoxidation catalysts on their performance, this contribution highlights the advantages of the aerosol procedure to synthesize mesoporous functionalized catalysts with very high dispersion of active sites.

Highlights

To improve heterogeneous catalyst performance, different approaches have been proposed, such as tuning the catalyst texture, controlling the nature and dispersion of the active sites, and optimizing the reaction conditions
We succeeded in preparing hydrophobic mesoporous Ti-SiO2 catalysts with effective methyl-functionalization, controlled texture, and improved Ti dispersion through the aerosol-assisted one-pot sol-gel procedure
Beyond the control of the textural properties such as specific surface area and pore size distribution, the aerosol route proved its superiority at obtaining high Ti dispersion, maximizing the amount of the catalytically active Ti species (FW-Ti), despite the addition of the methyl precursor

Summary

Introduction

To improve heterogeneous catalyst performance, different approaches have been proposed, such as tuning the catalyst texture, controlling the nature and dispersion of the active sites, and optimizing the reaction conditions. Another interesting approach is the adjustment of the hydrophobic/hydrophilic balance of the catalyst surface, which regulates the interaction between the catalyst and the reactants and products and, if well-adjusted, leads to more efficient adsorption of the reactants and desorption of the products. The accepted mechanism for the catalytic epoxidation of olefins with heterogeneous Ti-based catalysts is the Eley–Rideal mechanism [40,41,42], in which the oxidant adsorbs on the Ti active site and forms active intermediate species [40], which react with the olefin to produce the epoxide that desorbs from the catalyst

Methods

Results

Conclusion