Influence of acid–base properties of catalysts in the gas-phase dehydration–dehydrogenation of cyclohexanol on amorphous AlPO4 and several inorganic solids Original Research Article

A series of metal phosphates (Al, Fe, Ni, Ca and Mn) and stoichiometric (Al/Fe=Al/Ca=1) mixed systems: FeAl(PO4)2 and Ca3Al3(PO4)5, were prepared by an ammonia gelation method. Their amorphous character was determined through several physical methods: nitrogen adsorption, DRIFT and XRD patterns. Gas-phase competitive dehydration/dehydrogenation reaction of cyclohexanol was carried out as a probe reaction and cyclohexene was usually the main reaction product, but different amounts of 1- and 3-methylcyclopentenes as well as cyclohexanone were always obtained. These results were compared to those obtained with 17 commercial inorganic solids (several metal oxides, sulfates and phosphates). A main unexpected conclusion was that cyclohexanol dehydration is obtained not only in acid sites but also in basic sites.