ALPHA-ALUMINA-SUPPORTED NICKEL-CATALYSTS PREPARED FROM NICKEL ACETYLACETONATE - A TPR STUDY

Supported Ni catalysts with low metal loadings prepared by impregnatio n 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 calci nation temperature on the reduction profile, temperature of maximum re duction (T-M), and H-2/Ni ratio has been investigated. Metal-support i nteractions already exist at the impregnation step. The decomposition- reduction products of the organic moiety perturbing the TPR profiles a nd H-2 consumptions were suppressed when drying was done at 250 degree s C. Two distinct metal species could be distinguished according to th e calcination temperature. The one with T-M values less than or equal to 615 degrees C occurred at calcination temperatures less than or equ al to 400 degrees C, whereas at 600 degrees C and above, a second spec ies was characterized by T-M values of 900 degrees C and higher. The t wo species existed in different proportions in the solids calcined abo ve 400 degrees C and below 600 degrees C. Some indication supported th e formation of a nickel aluminate spinel-type phase when the solid was calcined at 600 degrees C and above accounting for the high temperatu res needed to reduce nickel oxide. (C) 1998 Academic Press.