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

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.

Titanosilicate Epoxidation Catalysts: A Review of Challenges and Opportunities

“…Actually, it appears that the effects of hydrophobization through co‐synthetic sol‐gel routes are hard to forecast because the presence of the organosilane in the synthesis tends to affect also the texture and the dispersion of the metal which complicates understanding and optimization of these systems [194,272] . To avoid such effect, it was recently proposed to produce methyl‐functionalized Ti−SiO 2 catalysts in one pot through the aerosol‐assisted sol‐gel process [273] . This straightforward route led to a series of catalysts with very similar textural properties and tunable degree of functionalization.…”

Photocatalytic Conversion of Organic Pollutants in Air: Quantum Yields Using a Silver/Nitrogen/TiO2 Mesoporous Semiconductor under Visible Light

“…As a result, and assuming complete methanol conversion into CO 2 , and adding Equations ( 9)- (12) gives the following equation:…”

“…This is given the properties of available semiconductors such as rapid charge recombination, low surface area, and high band gap (3.20 eV) [9]. To circumvent this, research is currently being conducted to develop a mesoporous TiO 2 photocatalyst [12,13] which can be used with near-ultraviolet (near-UV) light for wastewater treatment [14][15][16][17][18]. Nevertheless, these materials have not been investigated thoroughly for air treatment in the context of reaction engineering principles [19].…”

Hybrid Acid Catalysts Prepared via Grafting Trimethylsilyl Groups onto Aluminosilicates Synthesized by Non-Hydrolytic Sol-Gel

“…functionalization of hydrophilic groups on the surface of catalysts with hydrophobic groups) might differently influence the final hydrophobicity. [1][2][3][4][5][6] Also, in the case of zeolites, the post-synthetic modification can be performed by acid, 7,8 base, 9 or hydrothermal 10,11 treatment. These methods can lead to decreasing the number of defects in zeolites or even changing the silicon-metal ratio and thus make the zeolite surface more hydrophobic.…”