Effect of the ageing atmosphere on catalytic activity and textural properties of Pd/Rh exhaust gas catalysts studied by XRD

Effect of thermal, engine bench, and vehicle ageings on catalytic activity and support properties was evaluated mainly by XRD on a real catalytic system. The solid–solid phase transitions in the bulk material are of particular importance to catalyst behaviour after ageings. It was observed that the ageing atmosphere either accelerated or inhibited the phase transitions. The formation of aluminates was observed after ageings in inert and reducing atmospheres as well as after engine and vehicle ageings. The formation of aluminates is associated with the loss of specific surface areas that remained higher after reducing and inert ageings. The formation of cerium and lanthanum aluminates prevents the formation of low surface area α-Al2O3 that is responsible for the decrease in the total surface area. Catalytic activities also remained higher after reducing and inert ageings than after oxidizing ageing. Furthermore, laboratory ageing in reducing atmosphere seems to correlate best with the real vehicle ageing from the textural point of view.