Catalytic behaviour for skeletal rearrangement of hydrocarbons and surface structures of silica and alumina supported Pt-Mo catalysts

Abstract

The catalytic behaviour of silica and alumina supported Pt-Mo catalysts has been studied in the isomerization of hydrogenolysis of hexane hydrocarbons. XPS analyses were performed to follow the different oxidation states of molybdenum alone, or with platinum under hydrogen or under argon bombardment. The XPS analysis showed that molybdenum interacts more strongly with alumina than with silica. As a result, two classes of catalysts were identified, depending on the presence of the reduced relatively mobile, state of molybdenum on the catalyst surface. At low molybdenum content, the catalytic behaviour is similar to the platinum catalysts. But when the molybdenum concentration is increased another type of behaviour emerges, linked to a dual activity between platinum and molybdenum. It has been observed that hydrocarbon structure has a strong influence on the catalyst selectivity. When no tertiary carbon atoms are present in the hydrocarbon, the cracking reactions occur very deeply. Only secondary and primary carbon atoms are involved in the degradation process. The isomerization reaction is only a bond shift reaction.