LaMnO₃ reveals very high catalytic activity for methane combustion. Samples with the highest specific activity had the surface area 20-30 m²/g and were obtained by nano-technology methods (sol-gel processes, flame pyrolysis and flame hydrolysis). The alternative technique for synthesis of nano-size oxides consists in dispersion of active material on support with high surface area. This procedure is easier and more efficient in comparison with methods of nano-technology. In the present work, we compared catalytic characteristics of LaMnO₃ (5-20 mol%) supported on lanthana, Mn₂O₃, MgO and the same parameters of individual substrates. Mn-perovskite formed on support as a result of chemical interaction between carrier and metal oxide(s).The last one(s) formed at heat treatment of powder support impregnated by La and Mn nitrate solutions.

The rate constant for sample LaMnO₃/MgO with 5% at 550°C achieved 845 μmol/bar·s·g_LaMnO3(845 rc-unites) and exceeded the same characteristic for individual LaMnO₃ (20 m²/g), having the highest catalytic activity (700 rc-unites). It was revealed that increase of concentration leaded to decreasing of the rate constant down to 476 rc-unites as a result of agglomeration of nano-size particles supported LaMnO₃. Samples LaMnO₃/Mn₂O₃ showed similar behaviour but the values of the rate constant in this case were lower. This fact correlated with support surface area. The experimental data concerned to lanthana in contrast to MgO and Mn₂O₃ showed that activities of supported catalysts and pure support were comparable and there were some difficulties to calculate activity referred to LaMnO₃.

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1. Catalytic activity for methane flameless combustion and thermal stability of nano-sized lanthanum cobaltites doped with Ce, Pr and Tb