In-situ spectroscopic monitoring of the ambient pressure hydrogenation of C2 to ethane on Pt(111)

Abstract

The hydrogenation of C2 molecules formed on the Pt(111) surface through acetylene exposure at 750K was monitored in-situ with reflection absorption infrared spectroscopy (RAIRS) in the presence of up to 10Torr of H2. The coverage of post-reaction surface carbon was measured with Auger electron spectroscopy. The RAIR spectra show that C2 is hydrogenated to an ethylidyne intermediate. The hydrogenation of ethylidyne was also monitored at 400K for H2(g) pressures of 1.0×10−2 to 10Torr. At H2(g) pressures greater than 1.0Torr, ethylidyne is completely hydrogenated. In an attempt to probe the nature of the C2 adsorption sites, RAIR spectra of coadsorbed CO were obtained. It is found that while C2 does not block CO adsorption, the spectra indicate that the surface carbon is free of hydrogen. In contrast, ethylidyne blocks CO adsorption sites. In the presence of coadsorbed CO, complete hydrogenation of ethylidyne occurs at 450K versus 400K in the absence of CO.