Effect of Ni-aluminate support for enhancing activity of Pd based three-way catalyst

Three-way catalystic performances of Pd catalyst supported on Ni-aluminate was superior than those supported on other supports. Adsorption and reducti on properties of Ni-aluminate were investigated. The surface Ni2+ sites in Ni-aluminate were shown to act the adsorption sites of NO under both oxidat ive and reductive conditions. Under reductive conditions, in particular the Ni2+ sites cropped out abundantly resulting in a great increase in the qua ntity of NO adsorption. Ni-aluminate had higher resistance to the reduction with H-2, allowing to be reduced at 800 degreesC and, after the reduction, Ni-aluminate nearly recovered its previous state through a reverse process of re-oxidation. The reduction with H-2 was enhanced by the presence of su pported Pd; Partial reduction occurred at about 400 degreesC, and the reduc tion peaks on the high temperature region shifted by about 50 degreesC. As confirmed from the activity test by using a model gas mixture (C3H6-NO-O-2) , the Ni-aluminate supported Pd catalyst was more efficient in light-off ac tivity and NOx conversion activity under both stoichiometric and rich atmos phere than the Pd catalyst supported on gamma -Al2O3. Based on these result s, the excellent catalytic activity of the Ni-aluminate supported Pd cataly st is considered to show up through a mechanism in which the Ni-aluminate p rovides the adsorption sites for NO and transfer the adsorbed NO species to the catalytic reaction sites of Pd.