Sum frequency generation: Surface vibrational spectroscopy studies of catalytic reactions on metal single-crystal surfaces

Abstract

Abstract Sum frequency generation (SFG) has been used for molecular-level investigations of adsorbates under both ultrahigh vacuum and high-pressure catalytic reaction conditions to characterize several important catalytic reactions on platinum single crystals. These reactions include ethylene hydrogenation, propylene hydrogenation and dehydrogenation, cyclohexene hydrogenation and dehydrogenation, and carbon monoxide oxidation. From SFG spectra, important catalytic reaction intermediates were determined, and possible reaction spectator species were also identified. For ethylene and propylene hydrogenation, important reaction intermediates were determined to be π-bonded ethylene and propylene, respectively. During cyclohexene hydrogenation, 1,3-cyclohexadiene was observed to be the important reaction intermediate on both Pt(111) and Pt(100). By comparing SFGspectra characterizing cyclohexene dehydrogenation on Pt(111) and on Pt(100), it was determined that 1,3-cyclohexadiene is also an important reaction intermediate. Another intermediate, 1,4-cyclohexadiene, was also observed under dehydrogenation conditions on Pt(111) but not on Pt(100). This species was determined to be a spectator species. During carbon monoxide oxidation, incommensurate CO species were determined to be important reaction intermediates.