Effect of thermal treatment on various characteristics of nickel/aluminum phosphate catalysts

Five Ni/AlPO4 samples containing 5-50 wt.% nickel were prepared by impregnation method, calcined at 400-1000 degrees C and reduced at 400 degrees C. The structural properties of the samples were determined by thermal analysis and X-ray diffraction (XRD) techniques, while the adsorption of nitrogen at -196 degrees C was used to elucidate their textural parameters. The catalytic conversion of cyclohexane on the prepared solids was investigated using a pulse microcatalytic technique. The thermal analysis of pure AlPO4 and 35 wt.% Ni/AlPO4 samples demonstrated the presence of crystalline aluminum phosphate phase. The presence of nickel greatly affected the position of exothermic peak of AlPO4 phase. The X-ray diffraction lines of the investigated samples suggest the role of both nickel content and calcination temperature on the crystallization of AlPO4 and nickel metal phases. The results of N-2-adsorption indicated that the surface areas evaluated for various Ni/AlPO4 samples studied were found to decrease on increasing their nickel content and calcination temperatures. The selectivity of cyclohexane was found to depend on the nickel content and thermal treatment of the solids employed. The dehydrogenation and hydrogenolysis of cyclohexane are parallel reactions and proceed on active sites of different natures. (C) 1999 Elsevier Science B.V. All rights reserved.