alpha-Alumina-supported nickel catalysts prepared from nickel acetylacetonate: A TPR study

Supported Ni catalysts with low metal loadings prepared by impregnation of alpha-alumina with nickel acetylacetonate (Ni(acac)(2)) have been studied by temperature-programmed reduction (TPR). The effect of the metal loading (between 0.4 and 1.7 wt%), washing and drying, and calcination temperature on the reduction profile, temperature of maximum reduction (T-M), and H-2/Ni ratio has been investigated. Metal-support interactions already exist at the impregnation step. The decomposition-reduction products of the organic moiety perturbing the TPR profiles and H-2 consumptions were suppressed when drying was done at 250 degrees C. Two distinct metal species could be distinguished according to the calcination temperature. The one with T-M values less than or equal to 615 degrees C occurred at calcination temperatures less than or equal to 400 degrees C, whereas at 600 degrees C and above, a second species was characterized by T-M values of 900 degrees C and higher. The two species existed in different proportions in the solids calcined above 400 degrees C and below 600 degrees C. Some indication supported the formation of a nickel aluminate spinel-type phase when the solid was calcined at 600 degrees C and above accounting for the high temperatures needed to reduce nickel oxide. (C) 1998 Academic Press.