Theoretical study of structure sensitivity on Au doped CeO2 surfaces for formaldehyde oxidation: The effect of crystal planes and Au doping

Abstract

Engineering the surface structure of ceria-based catalysts at the atomic scale is a powerful strategy for boosting catalytic performance. Here, we carried out density functional theory calculations to investigate structure–activity relationships of Au-CeO2 catalysts with (1 1 1), (1 1 0), and (1 0 0) surfaces exposed in common CeO2 nanopolyhedra, nanorods and nanocubes, respectively. On stoichiometric AuCe1-xO2(1 1 1), (1 1 0) and (1 0 0) catalyst surfaces, HCHO oxidation follows the Mars van Krevelen mechanism. Calculations show that the migration of Au atoms on the surface of AuCe1-xO2(1 1 0) leads to a more stable configuration and improved HCHO oxidation performance than the undistorted (1 1 0) surface. On defective AuCe1-xO2(1 1 0) and (1 0 0) surfaces, HCHO oxidation follows the co-action of the Langmuir-Hinshelwood and Mars van Krevelen mechanisms with HCHO and O2 co-participation and surface reduction by the removal of lattice oxygen. Adsorbed O2 species contribute to a decrease in the energy barriers of the reaction steps. With the easy reducibility and lower energy barriers, the defect surfaces are more conducive to HCHO oxidation than stoichiometric surfaces. Whether stoichiometric surfaces or defective surfaces, (1 1 0) is most active for HCHO oxidation with the lowest activation energy for the rate-determining step, followed by (1 1 1), and then (1 0 0). Microkinetic simulations offer additional support for this result. Dopant Au atoms activate surface oxygen, and decrease the formation energy of oxygen vacancies. Au also reduces the energy barriers of key reaction steps on AuCe1-xO2(1 1 1) (1 1 0) (1 0 0) surfaces as compared to the pristine ceria surfaces. These calculations provide insight into the interaction between Au and CeO2 with different surface terminations and the effect of the CeO2 crystal plane and their reactivity for HCHO catalytic oxidation.