HIGH-PRESSURE CATALYTIC PROCESSES STUDIED BY INFRARED-VISIBLE SUM-FREQUENCY GENERATION

The recent development of infrared-visible sum frequency generation (S FG), a surface-specific Vibrational spectroscopy, has helped bridge th e pressure gap between studies of heterogeneous catalysis under high v acuum and atmospheric pressure. This is achieved by in situ monitoring of surface species at high pressure via their SFG vibrational spectra and correlating the results with the simultaneously measured reaction rate using gas chromatography. Examples of systems studied include ol efin hydrogenation and carbon monoxide oxidation over the (111) crysta lline face of platinum. In these examples, the studies succeed in reve aling the molecular details of the surface reactions. Identification o f key intermediates and their concentrations has made it possible for the first time to calculate turn over rates per active surface species rather than just per exposed surface metal atom. In all cases, the ke y intermediate of the reaction is not detectable on the surface in UHV under similar temperatures. (C) 1998 Elsevier Science B.V.