Catalytic properties of La0.8A0.2MnO3 (A = Sr, Ba, K, Cs) and LaMn0.8B0.2O3 (B = Ni, Zn, Cu) perovskites 1.: Oxidation of hydrogen and propene

The perovskites La(0.8)A(0.2)MnO(3) (A = Sr, Ba, K, Cs) and LaMn0.8B0.2O3 (B = Ni, Zn, Cu) were studied as catalysts for the oxidation of lean mixtures of hydrogen or propene in the temperature range of 200-450degreesC (hydrogen) and 150-550degreesC (propene), respectively. The catalytic features were correlated with the redox behavior of the oxides as revealed by temperature-programmed reduction (TPR) experiments. The highest activity for hydrogen oxidation was found over strontium, barium and copper substituted manganites, whereas in the case of propene oxidation the copper substituted perovskite showed substantially lower activity, which was assigned to the stronger bonding of the produced carbon dioxide to the copper centers. The results are discussed with regard to the concepts of suprafacial and intrafacial catalysis. Apart from the temperature control, the occurrence of one or another of the two mechanisms is imposed by the nature of the substituted cation. (C) 2002 Elsevier Science B.V. All rights reserved.