Optimal compositional and structural design of a LaMnO3/ZrO2/Pd-based catalyst for methane combustion

The aim of this work was to identify the optimum synthesis conditions and the most effective technique for noble metal deposition in a perovskite/palladium-based catalyst for natural gas combustion. The solution combustion synthesis (SCS) of perovskite/zirconia-based materials was investigated, by starting from metal nitrates/glycine mixtures. Characterization and catalytic activity tests were performed on as-prepared powders and then repeated after calcination for 2 h at 900 °C in calm air. Calcination appeared to be beneficial in that, despite lowering the specific surface area, it promoted the simultaneous crystallization of both LaMnO3 and ZrO2 and the half-conversion temperature (T50), regarded as an index of catalytic activity, was lowered. Two phases, both active towards methane oxidation - lanthanum manganate and palladium oxide - were combined so as to evaluate their synergism in terms of catalytic activity. Pd was therefore added either via incipient wetness impregnation on LaMnO3·2ZrO2 or through a one-step SCS-based route. Characterization and catalytic activity tests followed suit. Optimal composition and preparation routes were found: T50 was lowered from 507 °C - pure LaMnO3 prepared via SCS - to 432 °C attained with a 2% (w/w) Pd load on pre-calcined LaMnO3·2ZrO2.