Dehydrogenation Mechanism of Liquid Organic Hydrogen Carriers: Dodecahydro‐N‐ethylcarbazole on Pd(111). Issue 33 (15th July 2013)

• Record Type: Journal Article
• Authors: Amende, Max; Schernich, Stefan; Sobota, Marek; Nikiforidis, Ioannis; Hieringer, Wolfgang; Assenbaum, Daniel; Gleichweit, Christoph; Drescher, Hans‐Jörg; Papp, Christian; Steinrück, Hans‐Peter; Görling, Andreas; Wasserscheid, Peter; Laurin, Mathias; Libuda, Jörg
• Is Part Of: Chemistry. Volume 19:Issue 33(2013)
• Page Start: 10854
• Page End: 10865
• Publication Date: 2013-07-15
• Subjects: Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201301323
• Languages: English
• ISSNs: 0947-6539

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>Dodecahydro‐<italic>N</italic>‐ethylcarbazole (H<sub>12</sub>‐NEC) has been proposed as a potential liquid organic hydrogen carrier (LOHC) for chemical energy storage, as it combines both favourable physicochemical and thermodynamic properties. The design of optimised dehydrogenation catalysts for LOHC technology requires a detailed understanding of the reaction pathways and the microkinetics. Here, we investigate the dehydrogenation mechanism of H<sub>12</sub>‐NEC on Pd(111) by using a surface‐science approach under ultrahigh vacuum conditions. By combining infrared reflection–absorption spectroscopy, density functional theory calculations and X‐ray photoelectron spectroscopy, surface intermediates and their stability are identified. We show that H<sub>12</sub>‐NEC adsorbs molecularly up to 173 K. Above this temperature (223 K), activation of CH bonds is observed within the five‐membered ring. Rapid dehydrogenation occurs to octahydro‐<italic>N</italic>‐ethylcarbazole (H<sub>8</sub>‐NEC), which is identified as a stable surface intermediate at 223 K. Above 273 K, further dehydrogenation of H<sub>8</sub>‐NEC proceeds within the six‐membered rings. Starting from clean Pd(111), CN bond scission, an undesired side reaction, is observed above 350 K. By complementing surface spectroscopy, we present a temperature‐programmed molecular beam experiment, which permits direct observation of dehydrogenation products in the gas phase during continuous dosing of the LOHC. We identify H<sub>8</sub>‐NEC as the main product desorbing from Pd(111). The onset temperature for H<sub>8</sub>‐NEC desorption is 330 K, the maximum reaction rate is reached around 550 K. The fact that preferential desorption of H<sub>8</sub>‐NEC is observed even above the temperature threshold for H<sub>8</sub>‐NEC dehydrogenation on the clean surface is attributed to the presence of surface dehydrogenation and decomposition products during continuous reactant exposure.</p> </abstract>