CATALYTIC BEHAVIOR FOR SKELETAL REARRANGEMENT OF HYDROCARBONS AND SURFACE-STRUCTURES OF SILICA AND ALUMINA-SUPPORTED PT-MO CATALYSTS

The catalytic behaviour of silica and alumina supported Pt-Mo catalyst s has been studied in the isomerization of hydrogenolysis of hexane hy drocarbons. XPS analyses were performed to follow the different oxidat ion states of molybdenum alone, or with platinum under hydrogen or und er argon bombardment. The XPS analysis showed that molybdenum interact s more strongly with alumina than with silica. As a result, two classe s of catalysts were identified, depending on the presence of the reduc ed relatively mobile, state of molybdenum on the catalyst surface. At low molybdenum content, the catalytic behaviour is similar to the plat inum catalysts. But when the molybdenum concentration is increased ano ther type of behaviour emerges, linked to a dual activity between plat inum and molybdenum. It has been observed that hydrocarbon structure h as a strong influence on the catalyst selectivity. When no tertiary ca rbon atoms are present in the hydrocarbon, the cracking reactions occu r very deeply. Only secondary and primary carbon atoms are involved in the degradation process. The isomerization reaction is only a bond sh ift reaction.