(392g) Relationships Between the Surface Electronic and Chemical Properties of Doped 4d and 5d Late Transition Metal Dioxides
Accelerated materials discovery is key to the achievement of many of our current technological goals aimed at reducing our dependence on fossil fuels and realizing green production of chemicals. Metal oxides catalyze a number of chemical reactions that lie in these focus areas. The chemical property that dominates trends in the observed activity in many of these applications is the adsorption energy of various intermediate species. One strategy to easily tune the adsorption energy to obtain desirable properties is by doping or mixing an oxide with a different transition metal species. Identification of such dopant-host pairs can be accelerated through models that relate their known chemical properties (e.g., electronegativity, atomic size) to desired chemical properties such as adsorption energies. Such models require an understanding of relationships between the atomic structure and composition and the electronic structure.
Density functional theory calculations were performed to elucidate the underlying physics describing the adsorption energies on doped late transition metal dioxide rutiles. Adsorption energies of atomic oxygen on doped rutiles MD-MHO2, where transition metal MD is doped into MHO2, were expressed in terms of a contribution from adsorption on the pure oxide of the dopant MD and perturbations to this adsorption energy caused by changing its neighboring metal cations and lattice parameters to that of the host oxide MHO2, which we call the ligand and strain effects, respectively. Our analysis of atom projected density of states revealed that the t2g-band center had the strongest correlation with adsorption energies. We show that charge transfer mediated shifts to the t2g-band center describe the ligand effect, and the radii of the atomic orbitals of metal cations can predict the magnitude and direction of this charge transfer. Strain produces systematic shifts to all features of the atom projected density of states, but correlations between the strain effect and the electronic structure were dependent on the chemical identity of the metal cation. The slope of these correlations can be related to the idealized d-band filling. This work elucidates the underlying physics describing adsorption on doped late transition metal oxides and establishes a foundation for models that use known chemical properties for the prediction of reactivity.