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

MPS-Authors
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Dostert,  Karl-Heinz
Chemical Physics, Fritz Haber Institute, Max Planck Society;

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O'Brien,  Casey
Chemical Physics, Fritz Haber Institute, Max Planck Society;

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Liu,  Wei
Theory, Fritz Haber Institute, Max Planck Society;
Nano Structural Materials Center, School of Materials Science and Engineering, Nanjing University of Science and Technology;

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Riedel,  Wiebke
Chemical Physics, Fritz Haber Institute, Max Planck Society;

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Savara,  Aditya Ashi
Chemical Physics, Fritz Haber Institute, Max Planck Society;

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Tkatchenko,  Alexandre
Theory, Fritz Haber Institute, Max Planck Society;

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Freund,  Hans-Joachim
Chemical Physics, Fritz Haber Institute, Max Planck Society;

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Citation

Dostert, K.-H., O'Brien, C., Liu, W., Riedel, W., Savara, A. A., Tkatchenko, A., et al. (2016). Adsorption of isophorone and trimethyl-cyclohexanone on Pd(111): A combination of infrared reflection absorption spectroscopy and density functional theory studies. Surface Science, 650, 149-160. doi:10.1016/j.susc.2016.01.026.


Cite as: http://hdl.handle.net/11858/00-001M-0000-0029-D65C-7
Abstract
Understanding the interaction of α,β-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 α,β-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 + vdWsurf) 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 (d5-) 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 CH3 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 π 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 π 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.