A05: Quantum Chemical Investigation of Catalytic Cycles on Transition Metal Oxides

Prof. Dr. Christof Hättig

Electronic and molecular structure calculations provide additional insights into reaction mechanisms and properties which complement experimental results. In this project we apply electronic structure calculations within an embedded cluster approach where a quantum mechanically described structure model is embedded in a periodic electrostatic potential to account for the Madelung potential of ionic crystals. The embedded cluster approach allows to apply the broad range of tools for searching reaction pathways and modern electronic structure methods beyond semi-local density functional theory as e.g., hybrid functionals or random phase approximation (RPA) methods for calculations beyond DFT.

The aim of this project is to find and characterize in collaboration with the experiment and theory projects important intermediate and rate limiting steps of catalytic redox reactions on transition metal oxide surfaces. Thereby the project will contribute to unravel the reaction mechanisms for oxidation reactions on such surfaces. In the first funding period we have established the methodology and structure models for different CoFe₂O₄ surfaces and studied the chemi- and physisorption of water, alcohols and oxygen species as well as the formation of defects and first reactions on these surfaces in contact with vacuum or a gas phase. In the second funding period this approach will be extended to the liquid phase by combining the embedded cluster approach with a polarizable continuum model to account for the bulk solvent and explicit water molecules where they participate in reactions or modify the electronic or molecular structure of the surface. Furthermore, it is planned to extend the electronic and molecular structure calculations to molecular models which should allow for a closer comparison between theory and experiment.

(Figure: Top and side views of the electrostatically embedded cluster models validated for investigation of local events. The clusters were built symmetrically around the (A) Fe²⁺ and (B) Co²⁺ active sites at the (001)_Co-A surface, and the (C) Co³⁺ site and oxygen vacancy at the (001)_Co-B surface of CFO. The oxygen vacancy is marked by a yellow dashed circle).