Catalytic conversion of ethanol over nickel salts of Keggin type heteropolyacids supported on mesoporous silica

Some heteropoly salts-mesoporous silica composites were prepared from the Ni salt of molybdophosphoric acid NiHPMo12O40 (NiHPM) by supporting on SBA-15 mesoporous silica in different concentrations (20-40 wt% NiHPM) of active phase. The dehydration of ethanol was used to probe the catalytic properties of the NiHPM samples incorporated on the silica matrix. The main reaction products obtained on acid catalytic centers were ethylene and diethyl ether, besides acetaldehyde which was obtained on redox catalytic centers. It is shown that silica-supported catalysts appeared to be more active than bulk NiHPM catalyst in dehydration and dehydrogenation reactions. The higher values of dehydration and reaction product formation are obtained with the lowest loadings (20 and 30 wt% NiHPM) and as a consequence, the highest dispersion of active phase. In order to study the deactivation/regeneration of catalysts the ethanol conversion and the carbon selectivity to the primary compounds (ethylene, acetaldehyde, diethyl ether) were investigated during time on stream (TOS) for 600 min. The behavior of the other supported catalysts with 20 and 40 NiHPM wt% loading is very similar with 30NiHPM/SBA-15. Thermal analysis coupled with MS of spent catalysts confirms the presence of coke on all tested catalysts.