Molecular surface studies of adsorption and catalytic reaction on crystal (Pt, Rh) surfaces under high pressure conditions (atmospheres) using sum frequency generation (SFG) - surface vibrational spectroscopy and scanning tunneling microscopy (STM)

Sum frequency generation (SFG) - surface vibrational spectroscopy and the scanning tunneling microscope (STM) have been used to study adsorption and catalyzed surface reactions at high pressures and temperatures using (111) crystal surfaces of platinum and rhodium. The two techniques and the reaction chambers that were constructed to make these studies possible are described. STM and SFG studies of CO at high pressures reveal the high mobility of metal atoms, metal surface reconstruction, ordering in the adsorbed molecular layer, and new binding states for the molecule. CO oxidation occurs at high turnover rates on Pt(111). Different adsorbed species are observed above and below the ignition temperature. Some inhibit the reaction, and others are reaction intermediates since their surface concentration is proportional to the reaction rate. The dehydrogenation of cyclohexene on Pt(100) and Pt(111) proceeds through a 1,3-cyclohexadiene surface intermediate. The higher dehydrogenation rate is related to the higher surface concentration of these molecules on the (100) crystal face.