Effect of Ni-aluminate Support for Enhancing Activity of Pd Based Three-way Catalyst

Abstract

Three-way catalystic performances of Pd catalyst supported on Ni-aluminate was superior than those supported on other supports. Adsorption and reduction properties of Ni-aluminate were investigated. The surface Ni²⁺ sites in Ni-aluminate were shown to act the adsorption sites of NO under both oxidative and reductive conditions. Under reductive conditions, in particular the Ni²⁺ sites cropped out abundantly resulting in a great increase in the quantity of NO adsorption. Ni-aluminate had higher resistance to the reduction with H₂, allowing to be reduced at 800 °C and, after the reduction, Ni-aluminate nearly recovered its previous state through a reverse process of re-oxidation. The reduction with H₂ was enhanced by the presence of supported Pd; Partial reduction occurred at about 400 °C, and the reduction peaks on the high temperature region shifted by about 50 °C. As confirmed from the activity test by using a model gas mixture (C₃H₆–NO–O₂), the Ni-aluminate supported Pd catalyst was more efficient in light-off activity and NO_x conversion activity under both stoichiometric and rich atmosphere than the Pd catalyst supported on γ-Al₂O₃. Based on these results, the excellent catalytic activity of the Ni-aluminate supported Pd catalyst is considered to show up through a mechanism in which the Ni-aluminate provides the adsorption sites for NO and transfer the adsorbed NO species to the catalytic reaction sites of Pd.