Effect of heat treatment on the properties of nickel/chromia and nickel/alumina catalysts

Two series of Ni/Cr2O3 and Ni/Al2O3 catalysts were prepared by the coprecipitation method and heat-treated at temperatures between 350 and 1050 degrees C in hydrogen atmosphere. BET surface area, metal dispersion and catalytic activity for deuterium exchange reaction between hydrogen and water vapour were measured. The effect of the heat treatment on the catalyst properties is strongly dependent on the support nature: for Ni/Cr2O3 catalysts the metal dispersion, as well as the intrinsic activity are severely affected, while for Ni/Al2O3 catalysts the metal dispersion is decreased, but only a weak effect on the intrinsic activity is observed. The low stability of the Ni/Cr2O3 samples is due to the weak metal-support adhesion and, at the same time, to the collapse of the chromia surface area during the thermal treatment. In the case of the Ni/Al2O3 samples the metal-support interaction is strong and, also, the alumina surface area is decreased gradually during the heat treatment. The results provide arguments for the model invoking the creation at the nickel-support interface of new highly active sites for the deuterium exchange reaction between hydrogen and water vapour.