Pt/Zeolite Catalysts for Soot Oxidation: Influence of Hydrothermal Aging

Abstract

Developments in diesel engines and gasoline direct injection (GDI) engines have spawned the requirement of soot oxidation catalysts that work well in both NO + O₂ and O₂. In this study, we found that supporting Pt on zeolites such as H-ZSM5 and USY may receive better soot oxidizers than commercial Pt/Al₂O₃ catalyst. Durability tests indicate that, even after the hydrothermal aging at 800 °C, the aged Pt/H-ZSM5 is still a better soot oxidizer than Pt/Al₂O₃ in NO + O₂, and the aged Pt/USY exhibits the best activity in O₂. Further explorations reveal that the NO₂ preferential adsorption on soot is dependent on acid sites both inside and outside micropores of zeolites, while the decomposition of surface oxygenated complexes (SOCs) can be promoted by strong acid sites on the external surface. These two factors contribute mainly to the high activity of the Pt/zeolite catalysts in NO + O₂ and O₂, respectively. Considering a relatively high external surface area is always essential to inhibiting the severe sintering of Pt, it is important to choose a zeolite support with a relatively large external surface area and a certain amount of acid sites after the hydrothermal aging