Title : Quantum chemical insight into catalyst durability
Abstract:
Automotive catalysts compose of various kinds of metals and metal oxides. By using multi-scale theoretical method combined with three dimensional Kinetic Monte Carlo method, the sintering behavior of Pt can be explained by the diffusions on support materials such as ceria, zirconia, and alumina. Catalyst deactivation, the loss over time of catalytic activity is a problem of great and continuing concern in the practice of industrial catalytic processes. If the efficacies of designed catalysts could be expected and judged prior to a series of experiments and duration with time course, developing process is much earlier and efficiently processed. In this review, our original sintering dynamics simulator provides better understanding of macro-scale deactivation mechanisms. Based on the micro scale quantum chemical calculations, bond strengths of support oxides and Pt-oxide of supports were investigated. Moreover, sintering simulations were carried out from modeled fresh catalysts referred by TEM microscopic data at 1073K. We investigated the Pt-oxide-support interaction on optimized geometries of Pt/γ-Al2 O3 and Pt/CeO2 . Pt-support interaction of Pt/CeO2 is much stronger than Pt/γ-Al2 O3 represented as adsorption energies, Pt-O binding energies and bond populations. The time-evolution of the platinum dispersion along with support sintering within the three dimensional area, 0.1μm×0.2μm×0.2μm explains how Pt sintering differs on each support. Pt nanoparticles on the γ-Al2 O3 support sintered significantly via agglomeration, whereas Pt supported on CeO2 does not sinter and remains almost same diameter as fresh condition. On the other hand, thermal stability of γ-Al2 O3 and Pt/CeO2 is different, γ-Al2 O3 decreased its specific surface in the rate of 15% and CeO2 decreased in the rate of 60%. This correlates with the binding energy of the oxygen-metal of supports. Other than automotive catalysts, gradual voltage drop more than 20000 hours usage of high-temperature proton exchange membrane fuel cells was expected
