Catalytic soot oxidation over dried colloidal sols consisting of CeO
2 and CeO
2-ZrO
2 solid solution was studied before and after loading Ag catalyst. Ag-unloaded CeO
2 exhibited a higher activity than CeO
2-ZrO
2, but their activities after Ag-loading were comparable possibly because Ag activated oxygen responsible for soot oxidation. The CeO
2-ZrO
2 sol exhibited higher thermal stability against sintering than CeO
2 sols and thus retained a higher soot oxidation activity after thermal ageing above 800°C.
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