Influence of sulfation and regeneration on Pt/Al2O3 for NO oxidation

Abstract

Because of the potential crisis of Pt/Al₂O₃ catalysts being poisoned by S-containing impurities in diesel exhausts, it is important to better understand the deactivation of SO₂ and its regeneration effects on Pt/Al₂O₃ catalysts. In this study, these effects induced by SO₂ on Pt/Al₂O₃ were studied as a function of SO₂ exposure time, and NO oxidation activity was investigated for different treated Pt/Al₂O₃ catalysts. The results show that the SO₂ exposure period seriously affects the catalytic ability, especially after a long period of the sulfation process. TEM, CO-DRIFTS, TGA, and STEM-EDS elemental mapping results show that Pt physical and chemical states, and SO_x species are considered to be essential parameters in the SO_x effects on the catalysts. It is found that partial regeneration in the samples with different SO₂ exposure times is primarily caused by an un-recoverable deactivation of edge and kinked Pt atoms during the sulfation process. Moreover, the mechanism of SO_x loading and its elimination through the NO oxidation process, investigated by in situ DRIFTS, provides further cognizance on SO_x species and their removal. The mechanism reveals a special intermediate SO_x species, and thus a possible way in which gaseous SO₂ and O₂ transform to sulfate on catalysts is expected.