Unraveling the nature of platinum group metal catalysts’ performance in NO reduction by CO: difference and relevance

Abstract

A CO-SCR reaction, capable of simultaneously removing NO and CO from vehicle exhaust gases, has garnered significant attention. PGM (platinum group metal) catalysts are still the preferred choice due to their exceptional catalytic efficiency. However, an in-depth understanding of these catalysts’ structure–performance relationship is still lacking. In this study, a series of PGM–CeO₂/Al₂O₃ catalysts were prepared with an identical metal loading. Employing operando infrared spectroscopy, we investigated the evolutions of intermediates and combined relevant characterization techniques with reaction kinetics analysis and DFT simulation calculations to elucidate the nature of the difference in activity. PGM–Al₂O₃ catalysts produced N₂O in the CO + NO reaction, while no significant N₂O generation was observed in PGM–CeO₂ catalysts. The activity of Pt-based catalysts was notably worse than that of other catalysts due to “CO poisoning”. Rh–CeO₂ catalysts exhibited optimal reactivity owing to the atomic dispersion of Rh, while some Rh atoms underwent sintering leading to decreased activity after aging. Although Pd nanoparticles suffered an increase in vertical height during aging, moderate adsorptions of CO and NO made the aged Pd–CeO₂ catalysts perform superior to others. It is evident that metal dispersion does not exclusively dictate catalytic performance; factors such as the local coordination environment of the metal and the adsorption properties of reactants on the metal play equally crucial roles.