Computational Modeling Study of the Solubility of Cerium at LaCoO3 Perovskite Surfaces

Atomistic computational modeling of the surface structure of the catalytically active perovskite LaCoO3 is reported in order to understand the effect of doping with tetravalent cerium cations, which enhances high-temperature catalytic oxidation processes such as CH4 combustion. In particular, solution energies have been calculated for the important (100) and (110) low index crystal faces. Three reactions for Ce4+ doping have been considered, two of which involve creation of La3+ vacancies or Co3+ reduction in stoichiometric LaCoO3, whereas the third relates to oxygen vacancy filling in reductively nonstoichiometric LaCoO3. We show that Ce4+ is considerably more soluble at the surface than in the bulk to a level of similar to 5 atom %, which agrees with experimental estimates by X-ray diffraction. We predict that the nature of the defect compensating reaction will be strongly dependent on oxygen partial pressure, and hence on the preparation conditions. The effect of Ce4+ doping on catalytic oxidation is discussed in terms of the relative redox behavior of Ce3+ and Co3+ and the availability of oxygen vacancies and surface lattice oxygen.