Adsorption of isophorone and trimethyl-cyclohexanone on Pd(111): A combination of infrared reflection absorption spectroscopy and density functional theory studies

SURFACE SCIENCE

卷:650

Article

Dostert, Karl-Heinz¹  O'Brien, Casey P.¹  Liu, Wei^1,3  Riedel, Wiebke¹  Savara, Aditya¹  Tkatchenko, Alexandre¹  Schauermann, Swetlana^1,2  Freund, Hans-Joachim¹ 

[1] Max Anck Gesell, Fritz Haber Inst, Faradayweg 4-6, D-14195 Berlin, Germany

[2] Univ Kiel, Inst Phys Chem, Max Eyth Str 2, D-24118 Kiel, Germany

[3] Nanjing Univ Sci & Technol, Sch Mat Sci & Engn, Nano Struct Mat Ctr, Nanjing 210094, Jiangsu, Peoples R China

关键词: Infrared spectroscopy;    Density functional calculations;    Palladium;    Isophorone;    Trimethylcyclohexanone;   

DOI  :  10.1016/j.susc.2016.01.026

来源: Elsevier

【 摘 要 】

Understanding the interaction of alpha,beta-unsaturated carbonyl compounds with late transition metals is a key prerequisite for rational design of new catalysts with desired selectivity towards C = C or C = O bond hydrogenation. The interaction of the alpha,beta-unsaturated ketone isophorone and the saturated ketone TMCH (3,3,5-trimethylcyclohexanone) with Pd(111) was investigated in this study as a prototypical system. Infrared reflection-absorption spectroscopy (IRAS) and density functional theory calculations including van der Waals interactions (DFT + vdW(surf)) were combined to form detailed assignments of IR vibrational modes in the range from 3000 cm(-1) to 1000 cm(-1) in order to obtain information on the binding of isophorone and TMCH to Pd(111) as well as to study the effect of co-adsorbed hydrogen. IRAS measurements were performed with deuterium-labeled (d(5-)) isophorone, in addition to unlabeled isophorone and unlabeled TMCH. Experimentally observed IR absorption features and calculated vibrational frequencies indicate that isophorone and TMCH molecules in multilayers have a mostly unperturbed structure with random orientation. At sub-monolayer coverages, strong perturbation and preferred orientations of the adsorbates were found. At low coverage, isophorone interacts strongly with Pd(111) and adsorbs in a flat-lying geometry with the C = C and C = O bonds parallel, and a 0-13 group perpendicular, to the surface. At intermediate sub-monolayer coverage, the C = C bond is strongly tilted, while the C = O bond remains flat-lying, which indicates a prominent perturbation of the conjugated it system. Pre-adsorbed hydrogen leads to significant changes in the adsorption geometry of isophorone, which suggests a weakening of its binding to Pd(111). At low coverage, the structure of the CH3 groups seems to be mostly unperturbed on the hydrogen pre-covered surface. With increasing coverage, a conservation of the in plane geometry of the conjugated pi system was observed in the presence of hydrogen. In contrast to isophorone, TMCH adsorbs in a strongly tilted geometry independent of the surface coverage. At low coverage, an adsorbate with a strongly distorted C = O bond is formed. With increasing exposure, species with a less perturbed C = O group appear. (C) 2016 The Authors. Published by Elsevier B.V.

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