Density Functional Study of H2O dissociation on Au/alpha-Fe2O3: first step of Water Gas Shift Reaction

SILVIA A. FUENTE; RICARDO M. FERULLO; PATRICIA G. BELELLI

Santiago

Congreso; 10th Congress of the World Association of Theoretical and Computational Chemists; 2014

WATOC

Iron oxides have been subject of many studies due to their importance in catalysis, geochemical and environmental processes. Hematite, alpha-Fe2O3, is very stable and after transformations is often the final structure of other iron oxides. The study of the interaction between iron oxide and water is important to understand the interface equilibrium, the surface structure and its reactivity for chemical processes. Gold nanoparticles supported on transition metal oxide are extremely active catalysts in CO oxidation and many other reactions. A strong dependence of gold catalytic activity on the nature of the support was observed experimentally. Among different oxides, Fe2O3 is considered one of the most active supports. In this work we evaluate the adsorption and dissociation of H2O on clean Fe2O3(0001) and on Au5/Fe2O3(0001) surfaces. In the last case, a nanoparticle of five Au atoms was firstly modeled on the surface. The calculations were performed at the Density Functional Theory (DFT) level with the Vienna Ab-Initio Simulation Package (VASP). For this type of systems where d electrons are strongly correlated, an effective on-site repulsion term (U) of a Coulombic-type to the DFT Hamiltonian was applied. The Nudged Elastic Band (NEB) method was used to find the activation energy of reaction. Calculations show that H2O adsorption energy on clean Fe2O3 is higher than on Au5/Fe2O3 (-1.21 eV and -0.86 eV, respectively). However, the reaction energy is more exothermic on Au5/Fe2O3 than on clean Fe2O3 (-0.55 eV and -0.06 eV, respectively). The resulting OH group obtained from H2O dissociation on Au5/Fe2O3 is finally linked to a nearby Fe ion of the surface. This result indicates that reaction would take place at the Au/oxide interface, as it was experimentally suggested.