Preparation and catalytic properties of cobalt salts of Keggin type heteropolyacids supported on mesoporous silica

Some heteropoly salts – mesoporous silica composites were prepared from Co salt of molybdophosphoric acid CoHPMo 12 O 40 (CoHPM) by supporting on mesoporous silica in different concentrations (20–40 wt% CoHPM) of active phase. The acidity of composites was studied by the adsorption of ammonia and its temperature programmed desorption – TPD using thermogravimetry. The evolved gases during the adsorption–desorption of ammonia on CoPM-silica composites were identified by online mass spectrometry coupled with thermal gravimetry technique. The elemental concentrations based on the relative area of XPS spectra components for Co 2p, Mo 3d, Si 2p and O 1s were obtained for the surface of CoHPM/silica. The dehydration of ethanol was used to probe the catalytic properties of the CoHPM samples incorporated on the silica matrix. The main reaction products obtained on acid (dehydration) catalytic centres were ethylene and diethyl ether, besides acetaldehyde which was obtained on redox (dehydrogenation) catalytic centres. It is shown that silica – supported catalysts, appeared to be more active than bulk CoHPM catalyst in dehydration and dehydrogenation reactions. The higher values of dehydration and reaction products formation are obtained with the lowest loading (20 wt% CoHPM) and as a consequence the highest dispersion of active phase. The ethanol conversion and the carbon selectivity to the primary compounds were investigated during time on stream in order to study the stability and regenerability of supported catalysts.