Operando Studies of the Catalytic Hydrogenation of Ethylene on Pt(111) Single Crystal Surfaces
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- 作者：Aashani Tilekaratne ; Juan Pablo Simonovis ; Maria Francisca L贸pez Fag煤ndez ; Maryam Ebrahimi ; Francisco Zaera
- 刊名：ACS Catalysis
- 出版年：2012
- 出版时间：November 2, 2012
- 年：2012
- 卷：2
- 期：11
- 页码：2259-2268
- 全文大小：459K
- 年卷期：v.2,no.11(November 2, 2012)
- ISSN：2155-5435
文摘
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鈥揳bsorption 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鈥揇 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鈥? 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鈥? range. In contrast, almost unit reaction probability was observed here in effusive collimated molecular beam experiments emulating intermediate pressure conditions.