Abstract
Propylsulfonic acid-functionalized mesoporous silica was prepared through in situ oxidization of mercaptopropyl groups with H2O2 during a template-free condensation of tetraethyl orthosilicate (TEOS) and 3-mercaptopropyltrimethoxysilane (MPTMS) under strong acidic condition. The obtained materials with 3−15 mol % loadings of sulfonic acid groups had surface areas up to 700 m2/g and pore sizes around 3.5 nm. The materials synthesized with TEOS prehydrolysis had larger surface areas, pore volumes, and average pore diameters than those synthesized without TEOS prehydrolysis. IR, TG, solid-state NMR, and S K-edge XANES analyses showed that all the mercaptopropyl groups were completely converted to propylsulfonic acid groups without decomposition of the organic moieties using H2O2 as the in situ oxidant in the synthesis procedure. The accessibilities of sulfonic acid centers were determined by ion-exchange with cations of various sizes. The functionalized materials were used as acid catalysts in esterification of acetic acid with methanol and acetalization of chlorobenzaldehyde with methanol. The results showed that the propylsulfonic acid-functionalized mesoporous silica prepared with TEOS prehydrolysis and in situ oxidation had similar catalytic activities as propylsulfonic acid-functionalized SBA-15 but higher than the counterparts synthesized without TEOS prehydrolysis or by postoxidation of mercaptopropyl groups with H2O2.
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