Energetics of Cyclohexene Adsorption and Reaction on Pt(111) by Low-Temperature Microcalorimetry

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• 作者：Ole Lytken ; Wanda Lew ; Jonathan J. W. Harris ; Ebbe K. Vestergaard ; J. Michael Gottfried ; Charles T. Campbell
• 刊名：Journal of the American Chemical Society
• 出版年：2008
• 出版时间：August 6, 2008
• 年：2008
• 卷：130
• 期：31
• 页码：10247-10257
• 全文大小：325K
• 年卷期：v.130,no.31(August 6, 2008)
• ISSN：1520-5126

文摘

The heat of adsorption and sticking probability of cyclohexene on Pt(111) were measured as a function of coverage using single-crystal adsorption calorimetry in the temperature range from 100 to 300 K. At 100 K, cyclohexene adsorbs as intact di-σ bonded cyclohexene on Pt(111), and the heat of adsorption is well described by a second-order polynomial (130 − 47 θ − 1250 θ²) kJ/mol, yielding a standard enthalpy of formation of di-σ bonded cyclohexene on Pt(111) at low coverages of −135 kJ/mol and a C−Pt σ bond strength of 205 kJ/mol. At 281 K, cyclohexene dehydrogenates upon adsorption, forming adsorbed 2-cyclohexenyl (c-C₆H_9,a) and adsorbed hydrogen, and the heat of adsorption is well described by another second-order polynomial (174 − 700 θ + 761 θ²) kJ/mol. This yields a standard enthalpy of formation of adsorbed 2-cyclohexenyl on Pt(111) at a low coverage of −143 kJ/mol. At coverages below 0.10 ML, the sticking probability of cyclohexene on Pt(111) is close to unity (>0.95), independent of temperature.