Microstructure and reactivity of supported bimetallic platinum-gold catalysts

In this paper an attempt is made to correlate the microstructure of a supported bimetallic catalyst system with its activity and selectivity. A series of bimetallic platinum-gold catalysts supported on high-surface-area nonporous Aerosil was prepared by the incipient wetness technique. The platinum-gold system is known to be partially miscible in the bulk with the possibility of alloy formation at high and low PtAu atomic ratios. The reducibility of the various metal components in these catalysts was determined by temperature-programmed reduction. Microstructural characterization of the catalysts was performed by using analytical and high-resolution electron microscopic techniques. The combination of elemental analysis by EDX and lattice fringe imaging by HREM of individual metal particles was used to determine the presence and location of the various components of this bimetallic system. The kinetic behavior for the n-hexane conversion reaction and the product selectivities toward dehydrocyclization, isomerization, and hydrogenolytic cracking were measured. The product selectivity trends in n-hexane conversion can be attributed mainly to geometric effects related to the relative distribution and interdispersion of the platinum and gold atoms in the Catalysts.