Effect of catalyst preparation on catalytic activity: VII. The Chemical Structures on Nickel/Alumina Catalysts: Their Impact on the Formation of Metal—Support Interactions

Abstract

In situ electron spectroscopy for chemical analysis (ESCA) experiments and microreactor studies have been used to examine the apparent occurrence of metal-support interaction on Ni/Al 2O 3 catalysts; suppression of hydrogen chemisorption does occur subsequent to hydrogen temperature-programmed desorption. The strong metal—support interaction type behavior can be reversed by exposure of the catalyst to oxygen or carbon monoxide. It is demonstrated that the catalyst in the SMSI type state is denuded of surface NiAl 2O 4 but surface nickel is detectable by ESCA; this nickel does not adsorb hydrogen. Depth profiling reveals an increase in the nickel/aluminum intensity ratio and the partial reappearance of NiAl 2O 4. A model is proposed to account for the suppression of hydrogen adsorption on nickel. The partial covering of the active center by [Al x O y ] n aggregates formed during the thermal disproportionation of NiAl 2O 4 forms the basis of this model.