Methane combustion on La-Sr-Ce-Fe-O mixed oxides:: bifunctional synergistic action of SrFeO3-x and CeOx phases

The catalytic deep oxidation of methane over perovskite-type mixed oxide catalysts is examined. Three groups of mixed oxides (i) La1-yCeyFeO3 (0.0 < y less than or equal to 0.5), (ii) La1-xSrxFeO3 (0.01 < x less than or equal to 0.5) and (iii) La1-x-ySrxCeyFeO3 (0.0 < x, y less than or equal to 0.3), containing La, Sr, Ce, Fe cations in various ratios were prepared and characterized by XRD, Mossbauer spectroscopy and O-2-TPD measurements. The catalysts are active in the temperature range of 440-740 degreesC. A maximum of activity appears for y = 0.3, in the series La1-yCeyFeO3 in a wide temperature range. The increase of Sr content in the series La1-xSrxFeO3 results in the enhancement of the reaction rates which is related to the presence of SrFeO3-x crystal phase that favors the surface reaction. The double substituted solids La1-x-ySrxCeyFeO3 show higher catalytic activity as compared to the activity of the two other examined perovskitic series which is related to the bifunctional synergistic action of CeO2 and SrFeO3-x crystal phases in the solids. (C) 2001 Elsevier Science B.V. All rights reserved.