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

The hydrogenation of C 2 molecules formed on the Pt(111) surface through acetylene exposure at 750 K was monitored in-situ with reflection absorption infrared spectroscopy (RAIRS) in the presence of up to 10 Torr of H 2 . The coverage of post-reaction surface carbon was measured with Auger electron spectroscopy. The RAIR spectra show that C 2 is hydrogenated to an ethylidyne intermediate. The hydrogenation of ethylidyne was also monitored at 400 K for H 2 (g) pressures of 1.0 × 10 − 2 to 10 Torr. At H 2 (g) pressures greater than 1.0 Torr, ethylidyne is completely hydrogenated. In an attempt to probe the nature of the C 2 adsorption sites, RAIR spectra of coadsorbed CO were obtained. It is found that while C 2 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 450 K versus 400 K in the absence of CO. [ABSTRACT FROM AUTHOR]