Liquid Organic Hydrogen Carriers: Model Catalytic Studies on the Thermal Dehydrogenation of 1-Cyclohexylethanol on Pt(111)

The molecule pair of 1-cyclohexylethanol and acetophenonerepresentsan interesting system for a chemical hydrogen storage cycle as itcombines two different classes of so-called liquid organic hydrogencarriers (LOHCs), namely hydrogenated, formerly aromatic cyclic hydrocarbonsand alcohols, i.e., hydrogenated carbonyls. In particular, the latterhave recently attracted much attention due to their favorable dehydrogenationtemperatures and the possibility to convert them directly into electricityin specially designed direct-LOHC fuel cells. Herein, we investigatethe temperature-triggered dehydrogenation reaction of 1-cyclohexylethanolto acetophenone on a Pt(111) model catalyst using synchrotron-basedtemperature-programed X-ray photoelectron spectroscopy. To obtaina complete picture of the reaction mechanism, we consider not onlythe individual surface reactions of 1-cyclohexylethanol and acetophenonebut also those of two potential dehydrogenation intermediates, namely,the partially dehydrogenated 1-cyclohexylethanone and 1-phenylethanol.We find a stepwise dehydrogenation of 1-cyclohexylethanol: the firststep around similar to 210 K at the alcohol moiety yields the ketone1-cyclohexylethanone. The second step above similar to 260 K at the cyclohexylgroup is accompanied by the loss of an H-atom at the molecule'smethyl group and leads to the formation of an acetophenone-like phenyl-C(O)-CH2 species at similar to 340 K. The same species are also identifiedin the surface reactions of acetophenone, 1-phenylethanol, and 1-cyclohexylethanonein this temperature range. Overall, the system shows good thermalrobustness: a complete dehydrogenation of the hydrogen-rich carrieroccurs without damage to the carbon framework.