CO Oxidation by Rutile TiO₂(110) Doped with V, W, Cr, Mo, and Mn

Abstract

We used density functional theory to study CO oxidation catalyzed by TiO 2 (110), in which some Ti atoms on the surface are replaced with V, Cr, Mo, W, or Mn. We find that in the presence of O, V, Cr, Mo, and W dopants at the surface bind an oxygen atom so that the dopant has formula MO (M ) V, Cr, Mo, W). Rutile doped with Mn does not take an oxygen atom from the gas phase. We find that these materials oxidize CO by a Mars-van Krevelen mechanism in which the role of the dopant is to facilitate the formation of oxygen vacancies. The energy of CO reaction with an oxygen atom from the surface layer decays linearly with the energy of vacancy formation ∆E v , whereas the energy of adsorption of O 2 at a vacancy is a linear function of ∆E v . These are the only two reactions in the mechanism whose energy varies from one doped oxide to another. Because they both depend on the energy of oxygen vacancy formation, the latter quantity is a good descriptor of catalytic activity. In deciding which intermediate reactions are most likely from an energetic point of view, we impose a "spin conservation" rule: a reaction that requires "flipping a spin" is too slow for catalysis. Because of this, we only consider reactions that conserve spin. We find that all the dopants studied here lower the energy of vacancy formation; therefore, the doped oxides are better oxidants than the undoped ones.

CO Oxidation Mechanism on CeO2-Supported Au Nanoparticles

“…20, 67 We examined CO oxidation at the Au−CeO 2 interface and found that, contrary to the typical M-vK mechanism, the Au NP binds CO during oxidation. Figure 8 shows the first half of the CO oxidation process by the M-vK mechanism.…”

Oxygen activation on oxide surfaces: A perspective at the atomic level

“…Oxides, different from semiconductors, are subject to self-doping either by native defects or unwanted impurities, the concentration of which is difficult to control experimentally [51]. Both lattice defects and impurity ions may adopt different charge states in the oxide lattice [20,43], a variability that leads to pronounced compensation effects and is less common in semiconductors. Finally, dopants may be electrically inactive in a wide-gap insulator, as thermal excitation is insufficient to promote electrons from defect states into bulk bands.…”

Layered sphere-shaped TiO 2 capped with gold nanoparticles on structural defects and their catalysis of formaldehyde oxidation

“…2A (B). the deficiency content, and the number of surface oxygen vacancies (Vo) (Kim et al, 2008;Petrik and Kimmel, 2011). The XPS spectra of O (1s), Ti (2p) and Au (4f) in the Au/TiO 2 -200 and Au/TiO 2 -400 samples are shown in Appendix A Fig.…”