Three-way catalytic performance of a Pd/Ce0.67Zr0.33O2–Al2O3 catalyst for automotive emission control: the role of pretreatment gas

Abstract

The influence of oxidizing, reducing and reacting pretreatment gases on an automotive Pd/Ce_0.67Zr_0.33O₂–Al₂O₃ catalyst is examined and characterized using catalytic performance tests, in situ DRIFTS, CO chemisorption, HRTEM, XPS, H₂-TPR and OSC. The pretreatment gas impacts both the Pd particle size and chemical state, giving oxidized state and less growth of Pd in oxidizing gas. In contrast, Pd is mainly in the metallic state and exhibits more growth in reducing gas. In addition, reducing gas pretreatment also increases the concentration of oxygen vacancies. As a result, the catalyst pretreated with oxidizing gas shows good catalytic performance for HC oxidation. Pretreatment with reducing gas not only promotes the conversion of CO, NO and NO₂, but also broadens the operation window. However, for the Pd/CZA-RG catalyst pretreated with reacting gas, based on the analysis of in situ DRIFTS, some active sites in the catalyst surface are blocked by strongly adsorbed HC species, hindering NO conversion.