Operando Studies of the Catalytic Hydrogenation of Ethylene on Pt(111) Single Crystal Surfaces

The hydrogenation of ethylene on Pt(111) single-crystal surfaces was studied by combining measurements of the kinetics of reaction using mass spectrometry detection with the simultaneous characterization of the species present on the surface using reflection–absorption infrared spectroscopy. The kinetics measured by us matches past reports on the same system, with zero- and first-order dependence on the partial pressures of ethylene and hydrogen, respectively, and extensive H–D exchange if D2 is used instead of H2. The reaction takes place in the presence of an alkylidyne surface layer, which forms immediately upon exposure of the clean surface to the reaction mixture and can be removed by hydrogen or another olefin but at rates 1–2 orders of magnitude slower than the ethylene-to-ethane conversion. The nature of the alkylidyne surface species changes slightly upon being exposed to high pressures of hydrogen, with the carbon in the terminal methyl moiety acquiring some sp2 character. Moreover, the alkylidyne hydrogenation rate shows an inverse relationship with H2 pressure and is reduced by the presence of olefins in the gas phase. Turnover frequencies for the olefin hydrogenation reaction under pressures in the Torr range are high, as reported repeatedly in the past, but the corresponding reaction probabilities are quite low, below the 10–4 range. In contrast, almost unit reaction probability was observed here in effusive collimated molecular beam experiments emulating intermediate pressure conditions.Funding for this project has been provided by a grant from the U.S. National Science Foundation.Peer reviewe

Cluster catalysis A Subtle form of recognition

Corma Canós, A. (2014). Cluster catalysis A Subtle form of recognition. Nature Nanotechnology. 9(6):412-413. doi:10.1038/nnano.2014.114S41241396Haack, P. & Limberg, C. Angew. Chem. Int. Ed. 53, 4282–4293 (2014).Quintanar, L. et al. J. Am. Chem. Soc. 127, 13832–13845 (2005).Oliver-Meseguer, J., Cabrero-Antonino, J. R., Dominguez, I., Leyva-Perez, A. & Corma, A. Science 338, 1452–1455 (2012).Okrut, A. et al. Nature Nanotech. 9, 459–465 (2014).Tilekaratne, A., Simonovis, J. P., Lopez Fagundez, M. F., Ebrahimi, M. & Zaera, F. ACS Catal. 2, 2259–2268 (2012).Öfner, H. & Zaera, F. J. Am. Chem. Soc. 124, 10982–10983 (2002).Hwu, H. H., Eng, J. & Chen, J. G. J. Am. Chem. Soc. 124, 702–709 (2002).Boyer, J. L., Rochford, J., Tsai, M.-K., Muckerman, J. T. & Fujita, E. Coord. Chem. Rev. 254, 309–330 (2010)

Abrupt increase in hydrogen diffusion on transition-metal surfaces during hydrogenation catalysis

A sharp increase in the rate of hydrogen isotope scrambling was identified during the hydrogenation of olefins with H2 + D2 mixtures on Pt(111) catalysts, which spectroscopic data suggest is due to a sudden increase in atomic hydrogen surface mobility because of a decrease in the size of the islands of the adsorbed hydrocarbons