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Dehydrogenation Mechanism of Liquid Organic Hydrogen Carriers: Dodecahydro‐ N ‐ethylcarbazole on Pd(111)
Author(s) -
Amende Max,
Schernich Stefan,
Sobota Marek,
Nikiforidis Ioannis,
Hieringer Wolfgang,
Assenbaum Daniel,
Gleichweit Christoph,
Drescher HansJörg,
Papp Christian,
Steinrück HansPeter,
Görling Andreas,
Wasserscheid Peter,
Laurin Mathias,
Libuda Jörg
Publication year - 2013
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201301323
Subject(s) - dehydrogenation , x ray photoelectron spectroscopy , desorption , chemistry , hydrogen storage , photochemistry , hydrogen , catalysis , thermal desorption spectroscopy , spectroscopy , analytical chemistry (journal) , adsorption , organic chemistry , chemical engineering , physics , quantum mechanics , engineering
Dodecahydro‐ N ‐ethylcarbazole (H 12 ‐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 12 ‐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 12 ‐NEC adsorbs molecularly up to 173 K. Above this temperature (223 K), activation of CH bonds is observed within the five‐membered ring. Rapid dehydrogenation occurs to octahydro‐ N ‐ethylcarbazole (H 8 ‐NEC), which is identified as a stable surface intermediate at 223 K. Above 273 K, further dehydrogenation of H 8 ‐NEC proceeds within the six‐membered rings. Starting from clean Pd(111), CN 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 8 ‐NEC as the main product desorbing from Pd(111). The onset temperature for H 8 ‐NEC desorption is 330 K, the maximum reaction rate is reached around 550 K. The fact that preferential desorption of H 8 ‐NEC is observed even above the temperature threshold for H 8 ‐NEC dehydrogenation on the clean surface is attributed to the presence of surface dehydrogenation and decomposition products during continuous reactant exposure.