Abstract
Key factors controlling the thermal and redox-cycle stability of Ag/SnO2 catalyst were investigated to establish the design concept of “self-regenerative” soot oxidation catalysts. The effect of thermal aging (in air at 1000°C) on the soot oxidation activity was tested for Ag catalysts supported on SnO2, CeO2, ZrO2, TiO2, and MgO and SnO2-supported Cu, Pd, Rh, Ru, and Pt. Ag/SnO2 is found to be the most effective catalysts in terms of both activity and thermal stability. XRD and EXAFS results showed that particle growth of metal or metal oxide by the thermal aging was the main reason of the decreased soot oxidation activity, and the supported Ag species on Ag/SnO2 showed high sintering-resistance owing to the Ag–O–Sn bonds at metal–support interface. The effect of redox aging at 800°C on the soot oxidation activity and structure of Ag/SnO2 was also studied. H2-reduction of Ag/SnO2 lead to the formation of the large (20nm) particles of Ag3Sn, which were then redispersed by the reoxidation treatment to small Ag nanoparticles. This self-regenerative property lead to no catalyst deactivation of Ag/SnO2 after successive redox treatments. It is concluded that the strong chemical interaction between silver and tin species (metallic and oxidic Sn) under both reductive and oxidative environments at high-temperature enables the design of highly sintering resistant Ag-based oxidation catalysts.
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