Effect of preparation parameters on SrTiO3 +/-delta catalyst for the flameless combustion of methane

Three SrTiO3+/-delta catalysts have been compared. One of them (T3) was prepared by the traditional sol-gel procedure, the other two through the flame hydrolysis (FH) technique, in the presence of either 1.5 mol excess of citric acid (sample T2) or 3 mol excess of tartaric acid (sample T1) as complexing agent in the precursor solution. All the catalysts possessed the perovskite-R-e structure, with some SrCO3 as impurity. T1 was more crystalline than the other two samples and showed the most active as catalyst for the flameless combustion of methane. Isolated Ti3+ ions were found in T3 by EPR analysis. while different EPR features were noticed with T I and T2 and attributed to Ti3+/O-3(-). A high concentration of isolated Ti3+ ions was observed with T1, accompanied by Ti4+/O-3(-) and by other paramagnetic species, probably Ti4+/O- and Sr2+/O-, not observed with the other samples. This difference between the samples T1 and T2, likely connected with the different temperature attained during the FH preparation process with the two different complexing agents, can explain the higher oxidising activity of the T1 sample.