Surface science at high pressures

Scanning tunneling microscopy (STM) and infrared-visible sum frequency generation (SFG) are two techniques that can be utilized to monitor surfaces during chemical change at high pressures and temperatures. STM studies reveal the massive restructuring of the Pt(110) crystal face at atmospheric pressures as the ambient gas changes from hydrogen, to oxygen, and to carbon monoxide. The platinum STM tip can be used for catalytic hydrogenation or oxidation of carbonaceous deposits at 300 K on the nanometer scale; the rate accelerating exponentially with increasing reactant pressure. The SFG vibrational spectra detect the reversible formation of new adsorbed carbon monoxide species above 100 Torr on Pt(111), that appear to be platinum-carbonyl clusters Pt-n(CO)(m), with (m/n) > 1 and a CO commensurate overlayer. During ethylene hydrogenation over Pt(111) the reaction intermediate appears to be weakly bound pi-bonded ethylene which produces most of the ethane, while ethylidyne and di-sigma bonded ethylene are spectators during the catalytic process. The surface concentration of pi-bonded ethylene is 4% of a monolayer during the turnover, which yields an absolute turnover rate 25 times higher than the turnover rate per platinum atom.