Effect of Aging Conditions on Model Pd Three-Way Catalysts

Palladium plays a critical role in automotive three-way catalysts (TWC). Three-way catalysts deactivate with time, and this paper explores the effect of different aging environments on the properties and performance of model Pd catalysts supported on alumina or ceria-zirconia (CZO). A systematic study is carried out to determine how different aging environments affect the oxidation state and dispersion of Pd. In addition, the influence of the support and the Pd particle size are discussed with special emphasis on its relationship to the activity in various oxidation reactions. The catalysts are extensively characterized by hydrogen and carbon monoxide chemisorption, temperature programmed reduction and oxidation, ex-situ and in-situ XRD, and XPS.  As probe reactions, the oxidation of CO, methane, and propylene are used, along with the water shift reaction.  The effect of aging high temperatures, either lean or rich, can have differing effects on metal particle size in this family of catalysts.