Template-free synthesis of mesoporous phenylsulfonic acid functionalized silica

Abstract

Mesoporous silica functionalized with phenylsulfonic acid was prepared by a simple template-free co-condensation of tetraethyl orthosilicate (TEOS) and 2-(4-chlorosulfonylphenyl)ethyltrimethoxysilane (CETS) under strong acidic condition. The obtained materials with 3–15 mol% loadings of phenylsulfonic acid were X-ray amorphous, but had large surface areas (420–620 m 2/g) and narrow pore-size distributions (0.3–1.0 nm PSD, estimated from the peak width at half maximum height) with pore diameters in the range of 3.5–5.0 nm. TEOS hydrolysis prior to the addition of CETS was found to be important in order to obtain functionalized silica materials of large mesopores and pore volumes. IR, TG and solid state NMR studies showed that most of the phenylsulfonic acid groups were incorporated into the silica materials without decomposition during the synthesis procedure. Moreover, most of the sulfonic acid sites are accessible by large cations such as tetramethylammonium (TMA +) and tetrabutylammonium (TBA +) ions. The materials were examined as acid catalysts in esterification of acetic acid with methanol and acetalization of chlorobenzaldehyde with methanol. The results showed that the functionalized amorphous silica materials synthesized with TEOS pre-hydrolysis had similar catalytic activities as that of phenylsulfonic acid-functionalized SBA-15, but higher activities than those of the counterparts synthesized without TEOS pre-hydrolysis or the propylsulfonic acid functionalized SBA-15.