Dehydrogenation of cyclohexane and isoamylenes on nickel and calcium-nickel phosphate catalysts

Abstract

In the dehydrogenation of C/sub 4/ and C/sub 5/ olefins on calcium-nickel-phosphate catalysts cracking and coke-formation take place, in addition to the main reaction. Reduction of the catalyst by the reaction medium increases the rate of secondary reactions and reduces diene yield in dehydrogenation of butylenes, which is due to the formation of zero-valent nickel on the surface of calcium-nickel phosphate catalyst. It was found possible in a number of studies to effect transition of Ni/sup 2 +/ ..-->.. Ni/sup 0/ during treatment of the catalyst with hydrogen. It may be assumed from these studies that to suppress cracking and coke-formation, it is necessary to introduce into the catalyst modifying additives, which prevent the reduction of bivalent nickel or block the reduced nickel. When studying dehydrogenation of cyclohexane on nickel catalysts it was found that the addition to the catalyst of zinc oxide and non-transition metal oxides results in the suppression of hydrogenolysis of cyclohexane. This paper presents results of an investigation of the transformation of cyclohexane and isoamylenes on calcium-nickel-phosphate catalysts modified by strontium and zinc cations. The effect of these modifiers on the reduction of calcium-nickel-phosphate catalysts was also studied. To compare the efficiency of modifiers, cyclohexane wasmore » dehydrogenated on alumino-nickel catalysts containing strontium and zinc cations.« less