Heterogeneous catalysis with gold from a theoretical perspective

Modern computational approaches based on density functional theory offer opportunities for exploring and understanding complex catalytic processes at a microscopic scale. Electronic structure calculations provide experimentalists with much needed insights into the chemical and physical processes that determine the properties of different types of catalysts.

Adsorption energies, E_ad, of O₂ (squares) and the barrier height, E_a, for O₂ dissociation (circles) as a function of the number of Ag impurity atoms in a unit cell. Transition state structures for O₂ dissociation are schematically depicted.

The project aims at understanding the mechanisms of oxidation reactions on gold-based catalysts such as nanoporous gold (npAu) at a microscopic level. It has been debated whether the catalytic properties of npAu are mainly due to structural features, i.e., the high number of low coordinated surface atoms. Experiments provided evidence that residual silver (present in very small concentrations) is crucial in terms of O₂ activation.

We have studied the fundamental aspects of Au catalysis using theoretical models represented by the flat Au(111) and the kinked Au(321) slabs with and without Ag impurities. The theoretical investigation of co-adsorption and reaction between CO and atomic O on the kinked Au(321) surface allowed us, for example, to rationalize the formation of CO₂ above 200K, observed in temperature programmed desorption studies of npAu. We have shown that Ag atoms incorporated into gold surfaces can facilitate the adsorption and dissociation of molecular oxygen on them. Therefore, the presence of the low-coordinated gold atoms is essential but apparently not sufficient for the catalytic activity of gold.

Lyudmila Moskaleva

References:

• L.V. Moskaleva, S. Röhe, A. Wittstock, V. Zielasek, T. Klüner, K.M. Neyman, M. Bäumer, Phys. Chem. Chem. Phys. 13 (2011) 4529.
• L.V. Moskaleva, V. Zielasek, T. Klüner, K.M. Neyman, M. Bäumer, Chem. Phys. Lett. 525-526 (2012) 87.

Cooperation partners: Thorsten Klüner, Oldenburg, Germany; Konstantin Neyman, Barcelona, Spain

Funding: DFG

For detailed information contact Lyudmila Moskaleva

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