Dicyclohexylmethane as a Liquid Organic Hydrogen Carrier: A Model Study on the Dehydrogenation Mechanism over Pd(111)
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We have studied the dehydrogenation of the liquid organic hydrogen carrier (LOHC) dicyclohexylmethane (DCHM) to diphenylmethane (DPM) and its side reactions on a Pd(111) single crystal surface. The adsorption and thermal evolution of both DPM and DCHM was measured in situ in ultrahigh vacuum (UHV) using synchrotron radiation-based high-resolution X-ray photoelectron spectroscopy (HR-XPS). We found that after deposition at 170 K, the hydrogen-lean DPM undergoes C-H bond scission at the methylene bridge at 200 K and, starting at 360 K, complete dehydrogenation of the phenyl rings occurs. Above 600 K, atomic carbon incorporates into the Pd bulk. For the hydrogen-rich DCHM, the first stable dehydrogenation intermediate, a double π-allylic species, forms already at 190 K. Until 340 K, further dehydrogenation of the phenyl rings and of the methylene bridge occurs, yielding the same intermediate that is formed upon heating of DPM to this temperature, that is, DPM dehydrogenated at the methylene bridge. The onset for the complete dehydrogenation of this intermediate occurs at a much higher temperature than after adsorption of DPM. This behavior is mainly attributed to coadsorbed hydrogen from DCHM dehydrogenation. The results are discussed in comparison to our previous study of DPM and DCHM on Pt(111) revealing strong material dependencies.
KeywordsLiquid organic hydrogen carrier X-ray photoelectron spectroscopy Model catalysis
The authors acknowledge financial support by the Deutsche Forschungsgemeinschaft (DFG) within the Excellence Cluster “Engineering of Advanced Materials” in the framework of the excellence initiative. The present work was supported by BMW Forschung und Technik GmbH. T. X. is grateful for a PhD scholarship from China Scholarship Council (CSC). P.W. acknowledges support by the ERC through his Advanced Investigator Grant (No. 267376). The European Union (COST Action CM 1104), the DFG and the Fonds der Chemischen Industrie are gratefully acknowledged for further support. The authors thank the BESSY staff for support during the beamtime and the Helmholtz-Zentrum Berlin for travel support and the allocation of synchrotron beamtime.
- 4.Pez G, Scott A, Cooper A, Cheng H, Bagzis L, Appleby J (2005) WO 2005/000457 A2Google Scholar