Methanol steam reforming: CO2-selective Pd2Ga phases supported on α- and γ-Ga2O3

Authors: Harald Lorenz, Ramona Thalinger, Eva-Maria Köck, Michaela Kogler, Lukas Mayr, Daniela Schmidmair, Thomas Bielz, Kristian Pfaller, Bernhard Klötzer, Simon Penner

Abstract:
A set of different Pd/Ga₂O₃ catalysts has been tested as suitable CO₂-selective catalysts in methanol steam reforming, formaldehyde steam reforming and formic acid decomposition. Special focus was put on two different polymorphic forms of Ga₂O₃, namely α-Ga₂O₃ and "y-Ga₂O₃ and their comparison to the use of the more common β-Ga₂O₃ as oxide support of small Pd particles. The formation of eventually CO₂- selective intermetallic Pd–Ga phases started at around 523K on both supports. Pd₂Ga atlow temperatures (between 523K and 673K) and generally PdGa at higher temperatures (at and above 673K) were the only intermetallic phases observed. Both thermodynamically metastable oxide supports transformed into the stable β-Ga₂O₃ structure at 873K reduction temperature. In contrast to previous studies, a highly CO₂-selective state in methanol steam reforming (CO₂ selectivity > 70%) could be established on both catalysts after reduction at 673K (α-Ga₂O₃) and 523K (α-Ga₂O₃), where the active state of the catalysts can be characterised as Pd₂Ga/α-Ga₂O₃ and Pd₂Ga/"y-Ga₂O₃, respectively. α-Ga₂O₃ itself is reasonably CO₂-selective in methanol steam reforming (∼80%), although not very active. In contrast, the "y-Ga₂O₃ polymorph is neither CO₂-selective, nor active and resembles the behaviour of β-Ga₂O₃. The high CO₂- selectivity of α-Ga₂O₃ is explained in terms of a higher surface basicity alongside efficient decarboxylation of intermediary formed formic acid. As crucial parameters for the observed CO₂-selectivity in methanol steam reforming, decarboxylation of formic acid and oxidation of formaldehyde proceeding efficiently via a low-temperature reaction channel over either oxide-supported Pd₂Ga intermetallic catalysts were identified.

Keywords:
Intermetallic compounds
Formic acid decomposition
X-ray diffraction
CO₂ selectivity
Pd₂Ga

Published in: Applied catalysis A: General  (Volume 453, Pages 1-402, 26 February 2013)

Publisher: Elsevier

ISSN Information: 0926-860X

Methanol steam reforming: CO2-selective Pd2Ga phases supported on α- and γ-Ga2O3

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