TPR studies of the effects of preparation conditions on supported nickel catalysts

Abstract

Temperature-programmed reduction (TPR) was used to characterize silica-supported nickel catalyst precursors with respect to the degree of interaction with the support and the metal oxide location by monitoring variations in the impregnation, drying and calcination stages of catalyst preparation. Three peaks at ~ 200, ~ 400 and ~ 500 °C were resolved in the TPR profile. The low temperature peak at ~200 °C was associated with the presence of Ni 3+ and had little influence on the subsequent reduction profile. The peak at ~400 °C was associated with the reduction of large nickel oxide crystallites in the small pores of the silica, with little or no interaction with the support. The peak at ~ 500 °C was associated with the reduction of small nickel oxide crystallites strongly attached to the support in the large pores of the silica. The TPR profile provides a useful ‘fingerprint’ for characterizing catalysts and for studying the effects of preparative variables on the final catalyst. The preparative stages which precede the drying stage (impregnation volume, time and successive impregnation) can be varied over wide limits without much effect, but those at and after this stage (drying, calcination, reduction) affect the TPR profiles and final catalyst performance markedly and require strict control, especially in industrial scale manufacture. The activity of the catalyst for cumene hydrogenolysis increases with the increasing proportion of the 500 °C TPR peak; this largely arises from the decrease in nickel crystallite size, which also accompanies an increase in the 500 °C peak.