Redox behavior of active PdOx species on (Ce,Zr)xO2-Al2O3 mixed oxides and its influence on the three-way catalytic performance

Two kinds of (Ce,Zr)(x)O-2-Al2O3 mixed oxides (designated as CZA-m and CZA-c) were prepared through mechanically mixed and co-precipitation method, and the corresponding supported Pd-only three-way catalysts calcined at different temperatures were investigated by XRD, N-2 adsorption, in situ DRIFTS, HRTEM, H-2-TPR and O-2-TPSR. The results show that PdOx species are mainly dispersed on Al2O3-rich grains surface in fresh catalyst, after thermal aging treatment, some PdOx species would migrate to (Ce,Zr)(x)O-2-rich grains surface due to the strong interaction of PdOx-(Ce,Zr)(x)O-2 and the sintering of alumina with loss of surface area. When thermally treated at 900-1000 degrees C, the interaction of both Al2O3-(Ce,Zr)(x)O-2 and PdOx-(Ce,Zr)(x)O-2-rich grains would be promoted, which enhances the thermal stability of PdO species and the reoxidation ability of Pd-0 to PdO under high temperature reaction conditions, especially for Pd/CZA-c catalyst. Meanwhile, more stable PdOx species which have strong interaction with support are formed and their reducibility is improved. Therefore, Pd/CZA-c catalyst exhibits better thermal stability than that of Pd/CZA-m. (C) 2014 Elsevier B.V. All rights reserved.