Sulphation and ammonia regeneration of a Pt/MnOx–CeO2/Al2O3 catalyst for NOx-assisted soot oxidation†
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/MnOx–CeO2/Al2O3, Pt/Al2O3 and MnOx–CeO2/Al2O3 catalysts were sulphated and regenerated with ammonia. The soot oxidation activity of poisoned Pt/MnOx–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.