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

Novel PdO/La 10 Si 6– x Co x O 27−δ /γ-Al 2 O 3 catalysts with applications to methane combustion were developed. These materials were based on the use of La 10 Si 6– x Co x O 27−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. Co 3+/2+ ions were also introduced into the original La 10 Si 6 O 27 lattice to enhance its redox properties. Temperature-programmed reduction measurements revealed that the oxygen supply was facilitated by introducing Co 3+/2+, where the reduction was observed at 290 °C for La 10 Si 6– x Co x O 27−δ ( x = 1.0), whereas no reduction was observed below 460 °C for La 10 Si 6 O 27 . Among the samples synthesized in this work, PdO/La 10 Si 6– x Co x O 27−δ /γ-Al 2 O 3 ( 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/La 10 Si 6 O 27 /γ-Al 2 O 3 .