Novel Catalysts for Methane Combustion Based on Cobalt-Doped Lanthanum Silicates Having an Apatite-type Structure.

Novel PdO/La10Si6-xCoxO27-δ/γ-Al2O3 catalysts with applications to methane combustion were developed. These materials were based on the use of La10Si6-xCoxO27-δ as a promoter because this compound has an oxide-ion conducting apatite-type structure that allows the smooth migration of active oxygen to the PdO activator. Co3+/2+ ions were also introduced into the original La10Si6O27 lattice to enhance its redox properties. Temperature-programmed reduction measurements revealed that the oxygen supply was facilitated by introducing Co3+/2+, where the reduction was observed at 290 °C for La10Si6-xCoxO27-δ (x = 1.0), whereas no reduction was observed below 460 °C for La10Si6O27. Among the samples synthesized in this work, PdO/La10Si6-xCoxO27-δ/γ-Al2O3 (x = 1.0) exhibited the highest catalytic activity, allowing the complete oxidation of methane at 310 °C, a temperature 80 °C lower than the 390 °C required when employing PdO/La10Si6O27/γ-Al2O3.