III International Conference

PP-II-101Undoped LaMnO 3 has a structure of perovskite with close to cubic lattice and possessrather low activity with regard to N 2 O decomposition (Fig.1). At low degree of Lasubstitution by Sr (x=0.1÷0.2) a perovskite with hexagonal lattice has been formed that can becharacterized by enhanced activity. Reaction running over both perovskite containing latticesis strongly inhibited both by water and oxygen. At higher Sr content (x=0.3÷0.4), dependingon preparation conditions, both reverse transfer from hexagonal to cubic structure, andadditional formation of the phase with a diffraction pattern similar to that of β-Sr 2 MnO 4 [1],that was related by us to (La 1-x Sr x ) 2 MnO 4 , can take place. The last of them is a structurecomposed of alternate layers of perovskite and SrO x and detected in parallel with perovskitephase at x range from 0.4 to 0.9. Samples containing such laminated perovskite-like phasepossess high activity both in the absence of H 2 O and O 2 , and in their presence. At that, surfacelayers composition prominently affects the activity of such samples. At highest degree of Lareplacement (x = 0.9 ÷ 1.0) Sr 4 Mn 3 O 10 has been formed. Although high active in N 2 Odecomposition, these samples lose their activity prominently in H 2 O and O 2 presence.Dependence of samples activity on the oxygen mobility is discussed as well.100laminatedperovskiteN 2O conversion, %8060402000.0 0.2 0.4 0.6 0.8 1.0XcubicperovskiteFig.1. N 2 O conversion vsLa replacement degree bySr (x) for La 1-x Sr x MnO 3series calcined at 900 o C.Reaction mixture composition:■ – 0.15% N 2 O inHe, ● - 0.15% N 2 O + 3%O 2 + 3% H 2 O in He.References.1. Mizutani, N., Kitazawa, A., Ohkuma, N., Kato, M., J. Chem. Soc. (Japan) Ind. Ed., 73 (1970)1097.349