Sulfation of Pt/Al2O3 catalyst for soot oxidation: High utilization of NO2 and oxidation of surface oxygenated complexes

▶ Modification of sulfates enhances the soot oxidation activity of Pt/Al2O3 in NO + O2. ▶ The sulfated Pt/Al2O3 promotes the preferential adsorption of NO2 on soot. ▶ The accelerated decomposition of SOCs by sulfates is observed by in situ FTIR. ▶ Highly reactive NO2+ species exits on the sulfated catalyst at high temperatures.

The sulfated Pt/Al2O3 catalyst was synthesized by impregnating H2SO4 on the Pt/Al2O3 catalyst. It exhibits higher catalytic activity than Pt/Al2O3 for soot oxidation under loose contact conditions in a feed flow containing NO and O2. Further studies ascribe its good activity to a synergistic effect between sulfate species and platinum. Firstly, the electronegative sulfate species may improve the oxidation-resistance of metallic platinum in the oxidizing atmosphere, which is important for achieving high NO ↔ NO2 ↔ soot recycling efficiency; Secondly, the sulfate species inhibit the NOx adsorption on the alumina support, leading to a preferential adsorption of NOx on the surface of soot rather than on the catalyst, and thus provide more chances for NO2-soot reaction to generate the surface oxygenated complexes (SOCs); Finally, the sulfate species can promote the further decomposition of these SOCs species, resulting in a high catalytic efficiency for soot oxidation.

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