Regeneration of thermally aged Pt-Rh/CexZr1−xO2-Al2O3 model three-way catalysts by oxychlorination treatments

Pt-Rh/CexZr1−xO2-Al2O3 with 0.6 and 1.0 wt.% noble metal loadings were prepared and characterized for their metal dispersion with respect to CexZr1−xO2-free Pt-Rh/Al2O3 in fresh, thermally aged and oxychlorinated states. Thermal ageing at 973 K led to loss of metal dispersion in all cases but to negligible effect on the dispersion of the CexZr1−xO2 component where present. Oxychlorination was able to fully recover metal dispersion in all cases but led to different effects on the redox properties of CexZr1−xO2 which appeared to be related to the metal loadings. Despite showing improved dispersion following regeneration, higher loaded catalyst showed no improvement in light-off performance for either NO reduction or CO oxidation and showed poorer oxygen storage (OSC) ability, particularly at higher temperatures. Lower loaded catalyst showed improved dispersion, improved OSC and reduced light-off temperatures for NO reduction and CO oxidation after oxychlorination compared to that in the thermally aged state.