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Dynamic Surface Processes of Nanostructured Pd2Ga Catalysts Derived from Hydrotalcite-Like Precursors

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Ota,  Antje
Inorganic Chemistry, Fritz Haber Institute, Max Planck Society;

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Kröhnert,  Jutta
Inorganic Chemistry, Fritz Haber Institute, Max Planck Society;

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Weinberg,  Gisela
Inorganic Chemistry, Fritz Haber Institute, Max Planck Society;

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Kasatkin,  Igor
Inorganic Chemistry, Fritz Haber Institute, Max Planck Society;

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Kunkes,  Edward L.
Inorganic Chemistry, Fritz Haber Institute, Max Planck Society;

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Girgsdies,  Frank
Inorganic Chemistry, Fritz Haber Institute, Max Planck Society;

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Hamilton,  Neil
Inorganic Chemistry, Fritz Haber Institute, Max Planck Society;

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Schlögl,  Robert
Inorganic Chemistry, Fritz Haber Institute, Max Planck Society;

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Behrens,  Malte
Inorganic Chemistry, Fritz Haber Institute, Max Planck Society;
University Duisburg-Essen, Faculty of Chemistry;

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Citation

Ota, A., Kröhnert, J., Weinberg, G., Kasatkin, I., Kunkes, E. L., Ferri, D., et al. (2014). Dynamic Surface Processes of Nanostructured Pd2Ga Catalysts Derived from Hydrotalcite-Like Precursors. ACS Catalysis, 4(5), 2048-2059. doi:10.1021/cs500465r.


Cite as: https://hdl.handle.net/11858/00-001M-0000-0019-79EB-4
Abstract
The stability of the surface termination of intermetallic Pd2Ga nanoparticles and its effect on the hydrogenation of acetylene was investigated. For this purpose, a precursor synthesis approach was applied to synthesize supported intermetallic Pd2Ga nanoparticles. A series of Pd-substituted MgGa-hydrotalcite (HT)-like compounds with different Pd loading was prepared by co-precipitation and studied in terms of loading, phase formation, stability and catalytic performance in the selective hydrogenation of acetylene. Higher Pd loadings than 1 mol% revealed an incomplete incorporation of Pd into the HT lattice as evidenced by XANES and TPR measurements. Upon thermal reduction in hydrogen Pd2Ga nanoparticles were obtained with particle sizes varying with the Pd loading from 2 to 6 nm. Formation of intermetallic Pd2Ga nanoparticles led to a change of the CO adsorption properties as was evidenced by IR spectroscopy. Dynamic changes of the surface were noticed at longer exposure times to CO and higher coverage at room temperature as a first indication of surface instability. These were ascribed to the decomposition into a Ga-depleted Pd-phase and Ga2O3, a process which was suppressed at liquid nitrogen temperature. The reduction of the Pd precursor at 473 K is not sufficient to form the Pd2Ga phase and yielded a poorly selective catalyst (26% selectivity to ethylene) in the semi-hydrogenation of acetylene. In accordance with the well-known selectivity-promoting effect of a second metal, the selectivity was increased to 80% after reduction at 773 K due to a change from the elemental to the intermetallic state of palladium in our catalysts. Interestingly, if air contact was avoided after reduction, the conversion slowly rose from initially 22 to 94% with time on stream. This effect is interpreted in the light of chemical response of Pd and Pd2Ga to the chemical potential of the reactive atmosphere. Conversely to previous interpretations, we attribute the initial low active state to the clean intermetallic surface, while the increase in conversion is related to the surface decomposition of the Pd2Ga particles