Aggregation and redispersion of silver species on alumina and sulphated alumina supports for soot oxidation

Abstract

Soot oxidation was conducted over Ag/Al₂O₃ and Ag/SO₄²⁻/Al₂O₃ catalysts. Spent catalysts were found to exhibit higher activities than fresh ones for soot oxidation in oxygen. Environmental transmission electron microscopy (ETEM) was performed for the catalytic oxidation of soot over fresh and spent catalysts. Aggregation of silver nanoparticles occurred significantly on the alumina support under very low oxygen pressure. On increasing the oxygen pressure, redispersion of large Ag particles was observed on both supports, which explains the superior activities of the spent catalysts. Sulphated alumina was found to anchor the silver species effectively and deter the migration of silver to soot particles. Hence, the aggregation of silver was alleviated over Ag/SO₄²⁻/Al₂O₃, leading to higher activity than the Ag/Al₂O₃ catalyst.