NO-C2H4 Reactions on the Surface of Stepped Pt(332)
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- 作者：Yuhai Hu ; Keith Griffiths
- 刊名：Journal of Physical Chemistry C
- 出版年：2007
- 出版时间：July 12, 2007
- 年：2007
- 卷：111
- 期：27
- 页码：9919 - 9926
- 全文大小：220K
- 年卷期：v.111,no.27(July 12, 2007)
- ISSN：1932-7455
文摘
NO-C2H4 interactions on the surface of stepped Pt(332) have been studied using Fourier transform infraredreflection-absorption spectroscopy (FTIR-RAS) and thermal desorption spectroscopy (TDS). IR data showthat pre-dosed C2H4 molecules suppress the adsorption of NO on the surface of Pt(332) to an extent dependingon both C2H4 coverage and the temperatures to which C2H4 pre-adlayers are annealed. At 90 K, the adsorptionof NO on step sites is significantly suppressed by C2H4 following exposures greater than 0.32 L. This site-blocking effect persists and is even enhanced when annealing C2H4 pre-adlayers to 200 K, a temperature atwhich the adsorbed C2H4 molecules are not dissociated. As annealing temperatures are increased beyond 260K, an ethylidyne species forms and is located on terraces. Consequently, the adsorption of NO on step sitesis restored but to an extent smaller than that on a clean Pt(332) surface. The IR spectra also indicate thatthere are no detectable intermediates resulting from direct chemical reactions between NO and C2H4/C2H4-derived hydrocarbons, which can promote N2 production. The co-adsorption of C2H4- and C2H4-derivedhydrocarbons does significantly promote N2 desorption, being dependent on the temperatures to which pre-dosed C2H4 adlayers are annealed. Annealing C2H4 adlayers to temperatures 
300 K significantly enhancesN2 desorption at temperatures below 400 K, giving rise to a peak at about 340-380 K. This low-temperatureN2 desorption disappears completely after annealing the C2H4 adlayers to >350 K. N2 desorption at ~460 Kappears to be slightly enhanced. NO dissociation is the rate-limiting step in the reduction of NO by C2H4-and C2H4-derived hydrocarbons. The contribution of C2H4- and C2H4-derived hydrocarbons to N2 desorptionis mainly attributed to 1) weakening of N-O bonds through an electron-donation effect; and 2) providing asource of reductants, i.e., H, CHx, C2Hx, and even C, which react with the atomic O from NO dissociation,leaving the surface with more vacant sites for further NO dissociation. The generation of CHx and C2Hxtherefore plays a central role in the NO reduction mechanism.
300 K significantly enhancesN2 desorption at temperatures below 400 K, giving rise to a peak at about 340-380 K. This low-temperatureN2 desorption disappears completely after annealing the C2H4 adlayers to >350 K. N2 desorption at ~460 Kappears to be slightly enhanced. NO dissociation is the rate-limiting step in the reduction of NO by C2H4-and C2H4-derived hydrocarbons. The contribution of C2H4- and C2H4-derived hydrocarbons to N2 desorptionis mainly attributed to 1) weakening of N-O bonds through an electron-donation effect; and 2) providing asource of reductants, i.e., H, CHx, C2Hx, and even C, which react with the atomic O from NO dissociation,leaving the surface with more vacant sites for further NO dissociation. The generation of CHx and C2Hxtherefore plays a central role in the NO reduction mechanism.