Cerium phosphate in automotive exhaust catalyst poisoning

摘要

Conditions leading to cerium phosphate poisoning of both model and fully formulated automotive exhaust catalysts have been investigated.Temperatures above 700 deg C favor the formation of cerium orthophosphate (CePO_4) as do rich engine operating conditions (i.e.excess fuel).No apparent differences were observed in the type or amount of cerium phosphate produced by impregnating ceria with Pt,Pd,or Rh.Cerium phosphate is produced both by reaction of ceria with gaseous H_3PO_4 (P_2O_5),and by reaction of ceria with other phosphorus compounds deposited on the catalyst (e.g.aluminum and zinc phosphates).These results provide the first direct evidence of a decrease in oxygen storage capacity associated with the irreversible conversion of CeO_2 to CePO_4,thus identifying CePO_4 formation as a high-temperature mode of catalyst deactivation.