Bimodal cesium hydrogen salts of 12-tungstosilicic acid, CsxH4−xSiW12O40, as highly active solid acid catalysts for transesterification of glycerol tributyrate with methanol

Abstract

Bimodal CsxH4−x[SiW12O40] (Csx-bimodal) with mesopores interconnected with micropores were synthesized from microporous CsxH4−x[SiW12O40] (Csx-micro) with x=1.0–2.5, which were prepared in advance by titrating an aqueous solution of H4[SiW12O40] with an aqueous solution of Cs2CO3, followed by treatment in refluxing ethanol to mainly dissolve the H4[SiW12O40] in the particles. Mesopore size distributions and their pore volumes changed depending on x in Csx-micro. Microporous Cs2.5-micro transformed into bimodal Cs2.5-bimodal with mesopores having average diameters of 3.7nm and large mesopore volumes. Although Cs2.5-bimodal exhibited only low catalytic activity for the decomposition of isopropyl acetate, post-treatment in H2SO4 enhanced the catalytic activity due to substitution of the Cs+ ions on the surface with H+. H2SO4-treated Csx-bimodal showed high activity toward transesterification of glyceryl tributyrate with methanol due to its strong acid strength and mesoporosity.