ABSTRACT
Simple perovskites, layered perovskites and perovskite-rocksalt intergrowth structures of high-temperature superconducting cuprates (HTSC) are currently finding applications in potential economical routes for the selective oxidation of hydrocarbons and for the decomposition of nitrogen oxides (N2O and NO) in the environment. In the A2BO4 systems, the design of the catalyst depends on (a) the selection of the B-element; (b) valency control by suitable cationic substitutions; (c) the synergistic effect between the elements; and (d) maintenance of an adequate surface area. These criteria are also applicable to substitutions in the ABO3 perovskites. Recently Misono et al (1997) have tested these catalysts for the oxidation of paraffins and for the decomposition of N-oxides using Srand Mn-doped La3+Co3+O3 oxides and LaCuO3 oxides. It was found that the oxygen desorption rate increases with x up to 0.6 in La2−xSrxCoO3 and that the synergistic effect between Sr and Co (or Mn and Cu) as well as fine particle sizes are important. LaNiO3 perovskite shows a unique behaviour in that it exhibits well-defined equilibrium phases in the oxygen-loss curve. Anion vacancy ordering is elucidated by ED in the anion-deficient oxides (Gai and Rao 1975; figure 6.1). Such phases are possible in other related perovskites and the phases may be important in catalysis.
