Experimental investigation of the activity and thermal stability of hexaaluminate catalysts for lean methane–air combustion Original Research Article

This paper reports a quantitative comparison between two metal-substituted hexaaluminate catalysts and supported Pd catalyst (3 wt.% Pd/γ-Al2O3). Measured species profiles in stagnation-flow boundary layers are used to infer reaction rates by heterogeneous catalysis. The Pd-substituted material (Sr0.5Pd0.5Al11O18−α) is suitable for low-temperature operation and the LaxSryMn0.4Al11O18−α (x/y=0.8, 0.9, and 1.1) material is a good high-temperature catalyst. A wide range of operating temperatures and methane-air equivalence ratios are considered. The LaxSryMn0.4Al11O18−α catalysts show good catalytic activity at temperatures up to 1100 °C and are insensitive to La/Sr ratio and coating thickness. The supported-Pd catalyst and the Sr0.5Pd0.5Al11O18−α exhibit similar hysteresis characteristics when exposed to temperatures around 900 °C. The supported Pd deactivates upon exposure to temperatures above 900 °C, but the Pd-substituted hexaaluminate maintains good catalytic activity after high-temperature exposure. The supported Pd is generally more active than either hexaaluminate, but can suffer permanent deactivation upon high temperature exposure.