Model Catalytic Studies of Liquid Organic Hydrogen Carriers: Dehydrogenation and Decomposition Mechanisms of Dodecahydro-N-ethylcarbazole on Pt(111)

[Image: see text] Liquid organic hydrogen carriers (LOHC) are compounds that enable chemical energy storage through reversible hydrogenation. They are considered a promising technology to decouple energy production and consumption by combining high-energy densities with easy handling. A prominent LOHC is N-ethylcarbazole (NEC), which is reversibly hydrogenated to dodecahydro-N-ethylcarbazole (H(12)-NEC). We studied the reaction of H(12)-NEC on Pt(111) under ultrahigh vacuum (UHV) conditions by applying infrared reflection–absorption spectroscopy, synchrotron radiation-based high resolution X-ray photoelectron spectroscopy, and temperature-programmed molecular beam methods. We show that molecular adsorption of H(12)-NEC on Pt(111) occurs at temperatures between 173 and 223 K, followed by initial C–H bond activation in direct proximity to the N atom. As the first stable dehydrogenation product, we identify octahydro-N-ethylcarbazole (H(8)-NEC). Dehydrogenation to H(8)-NEC occurs slowly between 223 and 273 K and much faster above 273 K. Stepwise dehydrogenation to NEC proceeds while heating to 380 K. An undesired side reaction, C–N bond scission, was observed above 390 K. H(8)-NEC and H(8)-carbazole are the dominant products desorbing from the surface. Desorption occurs at higher temperatures than H(8)-NEC formation. We show that desorption and dehydrogenation activity are directly linked to the number of adsorption sites being blocked by reaction intermediates.