The influence of surface coverage on textural, structural and catalytic properties of cesium salts of 12-molybdophosphoric acid supported on SBA-15 mesoporous silica

Abstract

The Cs salt of molybdophosphoric acid Cs 2.5H 0.5PMo 12O 40 (CsHPM) was supported on SBA-15 in the concentration of 20, 30 and 40 wt.% loadings. Because Cs acid salts are insoluble, the SBA-15 supported Cs-acid salts were prepared by two-step sequential impregnation and in situ reaction on the support. The structure and texture of these CsHPM/SBA-15 composites were studied by XRD, SEM-EDS, FT-IR and micro-Raman spectroscopy and N 2 adsorption. Thermal stability was investigated by thermogravimetric analysis (TGA), differential thermal analysis (DTA) and differential scanning calorimetry (DSC). The dehydration of ethanol was used to probe the catalytic properties of the CsHPM samples incorporated on the silica matrix. FT-IR and Raman studies demonstrated that CsHPM maintained its Keggin structure after deposition on mesoporous SBA-15, regardless of the active phase concentration. The values of specific surface area of pure CsHPM were increased by deposition on mesoporous silica support. The immobilization of CsHPM on mesoporous SBA-15 obviously increases the thermal stability of the Keggin structures in comparison with their parent bulk Cs salts. The main reaction products obtained on acid (dehydration) catalytic centres were ethylene and diethyl ether, and respectively acetaldehyde which was obtained on redox (dehydrogenation) catalytic centres. © 2012 Elsevier Inc. All rights reserved.