Sulphation and ammonia regeneration of a Pt/MnOx–CeO2/Al2O3 catalyst for NOx-assisted soot oxidation

Abstract

The sulphur resistance and regeneration strategy of soot oxidation catalysts are critical to the application of catalytic diesel particulate filters (CDPFs). In the present work, Pt/MnO_x–CeO₂/Al₂O₃, Pt/Al₂O₃ and MnO_x–CeO₂/Al₂O₃ catalysts were sulphated and regenerated with ammonia. The soot oxidation activity of poisoned Pt/MnO_x–CeO₂/Al₂O₃ was recovered completely after 30 min reduction in 500 ppm NH₃ at 550 °C. The amount, distribution and structure of sulphates were studied comprehensively for the sulphated and regenerated samples by thermogravimetric analysis (TGA), infrared (IR) spectroscopy, CO chemisorption and transmission electron microscopy (TEM). The NO oxidation of Pt catalysts was found to depend strongly on the particle size distribution, surface exposure and oxidation state of the precious metal. This, as well as the effect of the remaining surface sulphates, helped the regenerated catalysts achieve even higher catalytic activity for soot oxidation.