Preparation, characterization, and catalytic activity of molybdenum carbide or nitride supported on platinum clusters dispersed in EMT zeolite

Bimetallic Pt-Mo catalysts were prepared by vapor deposition of Mo(CO)(6) onto nanometer size platinum particles previously dispersed an EMT zeolite. Subsequent decomposition of the Mo precursor formed a supported molybdenum carbide phase whereas reaction of the precursor with ammonia formed a supported nitride phase. Results from high-resolution transmission electron microscopy and X-ray absorption spectroscopy at the Mo K and Pt Lm edges showed conclusively that highly dispersed particles containing both transition metals were synthesized by the vapor deposition method. Coverage of Pt by Mo suppressed both the total capacity for dihydrogen chemisorption and the catalytic activity for benzene hydrogenation. However, compared to monometallic Mo carbide or nitride clusters supported on EMT zeolite, the bimetallic catalysts were much more active in the catalytic reactions of n-heptane at 623 K. The low thickness of the carbide or nitride phase (about 0.3 nn) allowed for a synergistic influence of the Mo phase on the small areas of exposed Pt and/or a direct activation of the nitride or carbide for catalysis. (C) 1999 Academic Press.