Fundamental Aspects of Rare Earth Oxides Affecting Direct NO Decomposition Catalysis

The basic aspects of rare earth oxides (REOs) that affect their capacity for direct NO decomposition catalysis were investigated. A correlation between crystal structure and catalytic activity was found, which is related to the NO adsorption ability of the REOs. The crystal structure was the most important factor affecting direct NO decomposition over REOs, since the adsorption of NO was significantly dependent on the coordination environments of the rare earth cations within each crystal lattice. Among the REOs, cubic C-type oxides showed higher NO decomposition activities than those of the others. Within a series of C-type cubic REOs, the activity was typically dominated by the density of the surface basic sites, and the effects of particle morphology and lattice parameters were small.