The role of suprafacial oxygen in some perovskites for the catalytic combustion of soot

High specific-surface-area bulk perovskites (18–25 m2/g) have been synthesized by the combustion synthesis method as catalysts for the combustion of soot, a major pollutant emitted by diesel engines. The activity order for soot combustion was found to be LaCrO3>LaFeO3>LaMnO3, which is just the reverse of the intrinsic activity toward methane combustion, another major application field for perovskites. On the grounds of a characterization based on XRD, SEM, TEM, TPD, and TPR analyses as well as on reactive runs, the prevalent activity of the chromite catalyst could be explained by its higher concentration of suprafacial, weakly chemisorbed oxygen, which contributes actively to soot combustion by spillover in the temperature range 300–500 °C, but negligibly to methane combustion. The best catalyst prepared (La0.9K0.1Cr0.9O3−δ) could ignite soot combustion well below 400 °C, which is inside the range of temperatures reached at the exhaust line of a diesel engine. Maximization of the concentration of suprafacial oxygen is pointed out as the main pathway to follow for the development of new, more active catalysts.