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Ga-Pd/Ga2O3 Catalysts: The Role of Gallia Polymorphs, Intermetallic Compounds, and Pretreatment Conditions on Selectivity and Stability in Different Reactions

Authors

  • Liandi Li,

    1. State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan, 030001 (PR China)
    2. Department of Inorganic Chemistry, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4–6, 14195 Berlin (Germany), Fax: (+49) 30-8413-4405
    3. Graduate University of Chinese Academy of Sciences, Beijing, 100049, PR China
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  • Dr. Bingsen Zhang,

    1. Department of Inorganic Chemistry, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4–6, 14195 Berlin (Germany), Fax: (+49) 30-8413-4405
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  • Dr. Edward Kunkes,

    1. Department of Inorganic Chemistry, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4–6, 14195 Berlin (Germany), Fax: (+49) 30-8413-4405
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  • Dr. Karin Föttinger,

    1. Institute of Materials Chemistry, Vienna University of Technology, Getreidemarkt 9, 1060 Vienna (Austria)
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  • Dr. Marc Armbrüster,

    1. Max-Planck-Institut für Chemische Physik fester Stoffe, Nöthnitzer Str. 40, 01187 Dresden (Germany)
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  • Dr. Dang Sheng Su,

    1. Department of Inorganic Chemistry, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4–6, 14195 Berlin (Germany), Fax: (+49) 30-8413-4405
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  • Dr. Wei Wei,

    1. State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan, 030001 (PR China)
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  • Prof. Dr. Robert Schlögl,

    1. Department of Inorganic Chemistry, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4–6, 14195 Berlin (Germany), Fax: (+49) 30-8413-4405
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  • Dr. Malte Behrens

    Corresponding author
    1. Department of Inorganic Chemistry, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4–6, 14195 Berlin (Germany), Fax: (+49) 30-8413-4405
    • Department of Inorganic Chemistry, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4–6, 14195 Berlin (Germany), Fax: (+49) 30-8413-4405
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Abstract

A series of gallia-supported Pd-Ga catalysts that consist of metallic nanoparticles on three porous polymorphs of Ga2O3 (α-, β-, and γ-Ga2O3) were synthesized by a controlled co-precipitation of Pd and Ga. The effects of formation of Ga-Pd intermetallic compounds (IMCs) were studied in four catalytic reactions: methanol steam reforming, hydrogenation of acetylene, and methanol synthesis by CO and CO2 hydrogenation reactions. The IMC Pd2Ga forms upon reduction of α- and β-Ga2O3-supported materials in hydrogen at temperatures of 250 and 310 °C, respectively. At higher temperatures, Ga-enrichment of the intermetallic particles is observed, leading to formation of Pd5Ga3 before the support itself is reduced at temperatures above 565 °C. In the case of Ga-Pd/γ-Ga2O3, no information about the metal particles could be obtained owing to their very small size and high dispersion; however, the catalytic results suggest that the IMC Pd2Ga also forms in this sample. Pd2Ga/gallia samples show a stable selectivity towards ethylene in acetylene hydrogenation (≈75 %), which is higher than for a monometallic Pd reference catalyst. An even higher selectivity of 80 % was observed for Pd5Ga3 supported on α-Ga2O3. In methanol steam reforming, the Ga-Pd/Gallia catalysts showed, in contrast to Pd/Al2O3, selectivity towards CO2 of up to 40 %. However, higher selectivities, which have been reported for Pd2Ga in literature, could not be reproduced in this study, which might be a result of particle size effects. The initially higher selectivity of the Pd5Ga3-containing samples was not stable, suggesting superior catalytic properties for this IMC, but that re-oxidation of Ga species and formation of Pd2Ga occurs under reaction conditions. In methanol synthesis, CO hydrogenation did not occur, but a considerable methanol yield from a CO2/H2 feed was observed for Pd2Ga/α-Ga2O3.

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