NITRIC-OXIDE REDUCTION PERFORMANCE OF AUTOMOTIVE PALLADIUM CATALYSTS

Activity of three-way palladium catalyst was examined by means of a pulse-flam-microreactor. The effects of cerium on the catalytic properties of gamma-alumina-supported palladium for the reduction of nitric oxide were studied with X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (TPR). The reduction of nitric oxide on palladium catalysts is inhibited significantly by hydrocarbon. However, the reduction of nitric oxide was improved by the addition of cerium to the catalysts. The XPS and TPR studies showed that the presence of cerium provided, palladium oxide in a hard-reduced state and suppressed the chemisorption of hydrocarbons on the palladium oxide. Additionally,cerium could increase surface specific oxygen storage capacity and decrease the apparent activation energy for the rea;ltion CO+NO-->CO2-+-1/2 N-2. So a high conversion of NOx reduction could shift to higher A/F ratio.