Influence of oxychlorination treatments on the redox and oxygen storage and release properties of thermally aged Pd-Rh/CexZr1−xO2/Al2O3 model three-way catalysts

Model Pd-Rh/Al2O3 three-way catalysts with and without CexZr1−xO2 as oxygen storage component have been compared in their fresh, thermally aged and oxychlorinated treated surface states to determine the potential regenerating effects of the latter thermo-chemical treatments. Special attention has been made on the characterisation of the metal dispersion, redox properties and the oxygen storage and release properties of the catalyst following each of the treatment stages. It was found that thermal aging under the conditions employed leads to a loss of metal dispersion, but with negligible sintering of the ceria-zirconia mixed metal oxide. Loss of oxygen storage capacity is a consequence of the loss in metal area that results in a loss of interfacial contact with the storage component. Oxychlorination of the aged samples leads to even greater than 100% recovery of metal dispersion and a significant recovery of the oxygen storage capacity. As a consequence of these effects, catalytic activity for the CO/O2 and NO/H2/O2 reactions was shown to improve significantly. The role of residual chloride following regenerating treatment is discussed in terms of ceria reducibility.