Advanced TWC Technologies Using CeO2/ZrO2 Solid Solutions

The beneficial effects of CeO₂/ZrO₂ solid solutions on the performance of fully formulated Pt, Rh TWC (three-way-conversion) catalysts were measured using both stand dynamometer and FTP testing after severe engine aging. The performance advantages were consistent with an enhancement of the chemical promotional effects of CeO₂. These included increased effectiveness for CO and NOx conversion and to a lesser extent for HC compared to catalysts prepared with the same loading of Ce and Zr but no solid solution formation. Higher performance could be achieved with the CeO₂/ZrO₂ solid solution catalysts having half the Ce loading of conventional catalysts prepared with pure CeO₂.

The physico-chemical properties of the catalysts were characterized using both XRD and TPR. XRD was used to determine the degree of solid solution formation between CeO₂ and ZrO₂ and TPR was used to characterize the redox properties/oxygen storage of the catalysts before and after aging. Measurable promotional effects were only observed for Zr levels in excess of 18 mole% after severe engine aging. TPR analysis showed that fresh catalysts had strong coupling between the precious metals (PMs) and the CeO₂ reduction. However, after severe aging the pure CeO₂ containing catalysts lost their oxygen storage properties, but measurable redox activity was observed for the CeO₂/ZrO₂ solid solution-containing catalysts.