No abstract

This study reports surface characterizations of Pd/LaFeO 3 catalysts after aging in diesel engine simulated conditions. Thermal aging and support-induced effects on the nature of Pd species were investigated. LaFeO 3 was prepared via a sol-gel method to promote relatively high specific surface area (19 m 2 g −1 ). Subsequent impregnation from solutions using Pd(NO 3 ) 2 , Pd(acac) 2 or Pd(NH 3 ) 4 (NO 3 ) 2 precursor salts was examined by means of XPS and infrared spectroscopy on pre-activated catalysts under reductive atmosphere and aged ones under reactive conditions overnight at 500• C. Both techniques reveal that the degree of Pd dispersion and the reducibility of oxidic palladium species are correlated to the oxidation state of oxidic palladium species and depend on the nature of the precursor salt. Hence, impregnated samples using Pd(NH 3 ) 4 (NO 3 ) 2 and Pd(acac) 2 precursor salts, after calcination, lead to highly dispersed Pd 4+ species strongly interacting with the support. On the other hand, it was found that both the catalysts suffer from stronger deactivation phenomena than those affecting the catalysts prepared via Pd(NO 3 ) 2 .