Perovskite-type oxides, La1−xAxCo1−yBiyO3−δ (Ax = Ba0.2, Sr0.4; y = 0, 0.2) and La1−xSrxMO3−δ (M = Co0.77Bi0.20Pd0.03, x = 0, 0.2, 0.4) and perovskite-like oxides La1.867Th0.100CuO4−δ, Nd2−xAxCuO4−δ (Ax = Ba0.4, Ce0.2) and YBa2Cu3O7−δ were investigated. X-ray diffraction results revealed that all of the materials were single phase, and that the crystal structures of La1−xAxCo1−yBiyO3−δ, La1−xSrxMO3−δ, La1.867Th0.100CuO4−δ, Nd2−xAxCuO4−δ and YBa2Cu3O7−δ were cubic, orthorhombic, tetragonal (T-structure), tetragonal (T′-structure) and orthorhombic, respectively. Chemical analysis indicated that there were Co4+/Co3+ ions in La1−xAxCoO3−δ (Ax = Ba0.2, Sr0.4), Co2+/Co3+ and Bi5+/Bi3+ ions in La1−xAxCo0.8Bi0.2O3−δ (Ax = Ba0.2, Sr0.4) and La1−xSrxMO3−δ, Cu2+/Cu3+ ions in La1.867Th0.100CuO4−δ, Nd2CuO4−δ, Nd1.6Ba0.4CuO4−δ and YBa2Cu3O7−δ. After pre-treatment in H or He at certain temperatures, Cu+/Cu2+ ion couples appeared in the cuprate samples. Oxygen isotope exchange experiments indicated that the lattice O mobility in the Bi-doped catalysts were much higher than that in the Bi-free ones. TPR results showed that lattice O in the former samples could be reduced at temperatures lower than those in the latter samples. For the oxidation of CO, Bi-incorporated catalysts performed much better than the corresponding Bi-free catalysts. The Sr-substituted perovskites exhibited higher catalytic activities than did the Ba-substituted ones. The improved catalytic performance due to the Sr (or Ba)- and Bi-doping was believed to be associated with enhancements in O vacancy density and Con+/Co(n+1)+ (n = 2, 3) and Bi3+/Bi5+ couple redox ability, as well as in lattice O mobility. For the elimination of NO over La1−xSrxMO3−δ, La0.8Sr0.2MO2.90 performed the best. A 300C-reduced La1.867Th0.100CuO4−δ catalyst that possessed dual cationic and anionic defects and Cu+/Cu2+ couple exhibited a higher DeNO activity than did the fresh one. In the decomposition of N2O, 800C-treated Nd2−xAxCuO4−δ (Ax = Ba0.4, Ce0.2) and YBa2Cu3O7−δ samples were superior (in catalytic performance) to their fresh counterparts. Here, O vacancies were favorable for the formation of an essential N2O22− intermediate species in N2O activation, and the redox Cup+/Cu(p+1)+ (p = 1 and 2) couples involved in the N2O decomposition processes. It was concluded that there was a strong correlation either between the structural defect (mainly O vacancies) and catalytic activity, or between the redox [Con+/Co(n+1)+ (n = 2, 3), Bi3+/Bi5+, and Cup+/Cu(p+1)+ (p = 1 and 2) couples] catalytic performance of these materials for CO and NOx removal. The generation of O vacancies by A-site replacements favored the activation of O2 and NOx. The modification of B-site ion oxidation states by aliovalent ion substitution into A- and/or B-sites promoted the redox process of the catalyst. Both effects influenced the mobility of lattice O.

The Relationship of Structural Defect–Redox Property–Catalytic Performance of Perovskites and their Related Compounds for CO and NOx Removal. H.Dai, H.He, P.Li, L.Gao, C.T.Au: Catalysis Today, 2004, 90[3-4], 231-44