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Dehydrogenation of Dodecahydro‐ N ‐ethylcarbazole on Pd/Al 2 O 3 Model Catalysts
Author(s) -
Sobota Marek,
Nikiforidis Ioannis,
Amende Max,
Zanón Beatriz Sanmartín,
Staudt Thorsten,
Höfert Oliver,
Lykhach Yaroslava,
Papp Christian,
Hieringer Wolfgang,
Laurin Mathias,
Assenbaum Daniel,
Wasserscheid Peter,
Steinrück HansPeter,
Görling Andreas,
Libuda Jörg
Publication year - 2011
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.201101311
Subject(s) - dehydrogenation , catalysis , x ray photoelectron spectroscopy , materials science , carbazole , adsorption , photochemistry , decomposition , nial , chemistry , crystallography , chemical engineering , organic chemistry , intermetallic , metallurgy , alloy , engineering
To elucidate the dehydrogenation mechanism of dodecahydro‐ N ‐ethylcarbazole (H 12 ‐NEC) on supported Pd catalysts, we have performed a model study under ultra high vacuum (UHV) conditions. H 12 ‐NEC and its final dehydrogenation product, N ‐ethylcarbazole (NEC), were deposited by physical vapor deposition (PVD) at temperatures between 120 K and 520 K onto a supported model catalyst, which consisted of Pd nanoparticles grown on a well‐ordered alumina film on NiAl(110). Adsorption and thermally induced surface reactions were followed by infrared reflection absorption spectroscopy (IRAS) and high‐resolution X‐ray photoelectron spectroscopy (HR‐XPS) in combination with density functional theory (DFT) calculations. It was shown that, at 120 K, H 12 ‐NEC adsorbs molecularly both on the Al 2 O 3 /NiAl(110) support and on the Pd particles. Initial activation of the molecule occurs through CH bond scission at the 8a‐ and 9a‐positions of the carbazole skeleton at temperatures above 170 K. Dehydrogenation successively proceeds with increasing temperature. Around 350 K, breakage of one CN bond occurs accompanied by further dehydrogenation of the carbon skeleton. The decomposition intermediates reside on the surface up to 500 K. At higher temperatures, further decay to small fragments and atomic species is observed. These species block most of the absorption sites on the Pd particles, but can be oxidatively removed by heating in oxygen at 600 K, fully restoring the original adsorption properties of the model catalyst.