The Dynamics of Oxygen Storage in Ceria-Zirconia Model Catalysts Measured by CO Oxidation Under Stationary and Cycling Feedstream Composition

CeO2-ZrO2 is one of the main components of the new generation of three-way catalysts for the treatment of noxious pollutants from car exhaust. The dynamics of CO oxidation over a series of fresh and aged CeO2-ZrO2 catalysts of different composition were measured. The reaction under transient ″anaerobic environment″ (in both pulse and cycling mode) and steady-state conditions was performed to evaluate the varying contributions to oxygen storage/release capacity. Under stationary conditions, the presence of ZrO2 was of little or no benefit to stoichiometric CO oxidation, and the catalytic activity was strongly dependent on surface area and on the number of exposed Ce atoms. The highest performance level was achieved with pure CeO2. The beneficial effect of CeO2-ZrO2 mixed oxides on catalytic performance was seen when CO oxidation was performed in transient pulse mode or under cycling feedstream composition. In this case, catalysts having the composition CexZr1-xO2 with 0.5 < x < 0.8 indicated an increased catalytic effectiveness correlated to their oxygen storage capacity and redox activity. The promotional effect of ZrO2 was much more evident after severe aging.