Effect of M ion oxidation state in Sr1-xMxTiO3 +/-delta perovskites in methane catalytic flameless combustion

Sr1-xMxTiO3 +/-delta (x=0 or 0.1; M=K or Gd) have been compared as catalysts for the flameless combustion of methane. The samples were prepared both by traditional sol-gel (SG) and by flaine-hydrolysis (FH) procedure. All the catalysts possessed the perovskite-like structure, with some SrCO3 as impurity with Sr0.9K0.1TiO3 +/-delta prepared by SG procedure. All the samples prepared by FH were better catalysts than those prepared by SG. A further improvement in the catalytic activity was obtained with M = K, but only at temperatures lower than 550 degrees C. X-band and Q-band EPR spectroscopies provided an explanation of this observation, based on the high mobility of surface O-3(-) species on the surface of the (FH) Sr0.9K0.1TiO3 A sample.