BIMETALLIC CATALYSTS .6. SURFACE-COMPOSITION OF PT-MO SIO2 CATALYSTS - INFLUENCE OF REACTION MEDIA/

Bimetallic Pt-Mo catalysts deposited on silica show unusual behavior w hen used in reactions of hydrocarbons with hydrogen (hydrogenolysis, i somerization, dehydrocyclization). This can be explained by variations of the surface composition, i.e., the Mo/Pt surface ratio, with the c onditions, particularly the temperature and the composition of the gas phase in contact with the catalyst. Two methods for detecting such va riations have been used in this work: these are XPS analysis and the p roduct distribution in 3-methylpentane hydrogenolysis which is very se nsitive to the surface composition. Both methods have shown that the s urface composition of Pt-Mo/SiO2 catalysts is modified in the presence of aromatic hydrocarbons, the molybdenum surface content of metal par ticles being decreased compared with their original molybdenum content after reduction in hydrogen. (C) 1994 Academic Press, Inc.