Zheng Liu, Catalyst Technology and Emission Chemistry, Cummins Inc, 1900 McKinley Ave., CTC-MC 50183, Columbus, IN 47203, Michael D. Amiridis, Chemical Engineering, University of South Carolina, 2C02, Swearingen Engineering Center, Department of Chemical Engineering, 301 South Main Street, Columbia, SC 29208, and Yi Chen, Department of Chemistry, Nanjing University, Nanjing, China.
CuO catalysts supported on tetragonal ZrO2 (t-ZrO2), γ-Al2O3, and SiO2 supports were prepared by a conventional incipient impregnation method with variable CuO loadings. These catalysts were characterized by XRD, ESR, UV/Vis-DRS and TPR measurements and were used for the catalytic decomposition of N2O. The characterization results reveal significant differences in the structure of the surface Cu ion species formed on these supports with different surface structures. Furthermore, the nature of these species changes with CuO loading. More specifically, highly dispersed isolated and paired Cu2+ ions are formed at CuO loadings below their dispersion capacities on t-ZrO2 (8.6 Cu2+ ions/nm2) and γ–Al2O3 (5.1 Cu2+ ions/nm2), respectively. In contrast, crystallite-like CuO are the predominant species on SiO2, even at very low loadings. TPR results reveal that the dispersed CuO species formed on t-ZrO2, γ-Al2O3 and SiO2 have a different reducibility, presumably due to differences in the strength of the interaction between these species and the supports. The results of activity tests indicate that the catalytic activity for N2O decomposition over these catalysts with the same CuO loadings in the following order: CuO/t-ZrO2 > CuO/γ-Al2O3 >> CuO/SiO2. Finally, the catalytic activity of these catalysts for the decomposition of N2O can be directly correlated to the structure of the surface Cu ion species formed, as well as the strength of the interaction of these species with the support and is maximized over highly dispersed Cu2+ ions on t-ZrO2.