Zur fördernden Wirkung von Spuren von Silber in Gold-Nanokatalysatoren für die Epoxidation von Propen und die CO-Oxidation bei niedrigen Temperaturen: Mechanistische Untersuchung mit Dichtefunktional-Rechnungen
Physikalische Chemie von Festkörpern und Oberflächen, Materialcharakterisierung
Zusammenfassung der Projektergebnisse
This computational chemistry project was successful at generating new insights into elementary mechanisms responsible for the catalytic activity of unsupported gold-based oxidation catalysts. We have shown that silver impurities incorporated into these catalysts facilitate adsorption and dissociation of molecular oxygen both directly and indirectly (through stabilization of on-surface atomic oxygen, which self-catalyzes the O2 dissociation). Furthermore, we explored a set of reaction routes between CO and atomic O on the kinked Au(321) surface with Ag impurities. Our computational study helped interpret the results of O2 and CO adsorption/desorption experiments in UHV by the host group. Beyond that we studied the thermodynamic and kinetic stability of adsorbed atomic oxygen on gold-based catalysts with silver impurities as a function of temperature and pressure and explained why molecular oxygen dissociates on nanoporous gold at ambient pressure but not under UHV conditions. Our publications motivated related theoretical studies on gold surfaces with silver impurities as well as further experimental studies. The second central topic of the project was the selective epoxidation of propylene to propylene oxide (PO) on gold-based catalysts. PO is an important bulk chemical used for synthesis of many added value products. Currently there is a surge of interest in finding a simple and green process for PO synthesis. Promising results in terms of activity and selectivity have been achieved for propylene oxidation on supported gold catalysts with a mixture of O2 and H2 or with molecular O2 alone as oxidant. We studied a detailed transformation network of competitive reaction pathways following the initial steps of oxidation. Our calculations overruled some of the earlier assumptions regarding the mechanism of PO formation. We have explained why PO is not formed on gold unless hydrogen or water is used as co-reactant. Peroxo species are found to be responsible for the high selectivity of epoxidation on gold-based catalysts.
Projektbezogene Publikationen (Auswahl)
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Silver Residues as a Possible Key to a Remarkable Oxidative Catalytic Activity of Nanoporous Gold. Phys. Chem. Chem. Phys. 2011, 13, 4529-4539
L. V. Moskaleva, S. Röhe, A. Wittstock, V. Zielasek, T. Klüner, K. M. Neyman, M. Bäumer
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CO oxidation by co-adsorbed atomic O on the Au(321) surface with Ag impurities: A mechanistic study from first-principles calculations. Chem. Phys. Lett. 2012, 525-526, 87-91
L. V. Moskaleva, V. Zielasek, T. Klüner, K. M. Neyman, M. Bäumer
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Chapter 7.18 - From static to reacting systems on transition-metal surfaces. In: Comprehensive Inorganic Chemistry II: From Elements to Applications, Eds. J. Reedijk, K. Poeppelmeier, Vol. 7: Surface Inorganic Chemistry and Heterogeneous Catalysis, Eds. R. Schlögl, J.W. Niemantsverdriet, Elsevier, Oxford, 2013, pp. 475-503
S. M. Kozlov, H. A. Aleksandrov, L. V. Moskaleva, M. Bäumer, K. M. Neyman
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Chemisorbed oxygen on the Au(321) surface alloyed with silver: A first-principles investigation. J. Phys. Chem. C, 2015, 119 (17), pp 9215–9226
L. V. Moskaleva, T. Weiss, T. Klüner and M. Bäumer
