Designed synthesis of nanostructured Al2O3 stabilized homogeneous CeO2-ZrO2 solid solution as highly active support for Pd-only three-way catalyst

Abstract

In this work, a highly active CeO2-ZrO2-Al2O3(CZA2) support material was successfully fabricated and the activity of its supported Pd-only three-way was also characterized. Pd/CZA2-a (aged catalyst) could maintain a superior activity and thermal stability, the T50 of CO, NO, C3H8 and C3H6 over which decrease by 34 °C, 32 °C, 29 °C and 28 °C than that over Pd/CZA1-a (reference catalyst). As characterized, the superior activity of Pd/CZA2 associates closely with the highly porous structure and advanced reducibility of the support material. By N2 adsorption–desorption analysis, TEM and SEM analysis, CZA2 displays large pore volume (0.66 mL/g) and wider pore radius (25.3 nm), which benefits the diffusion of reactant in emissions with high space velocity. And such larger pore volume and pore radius of CZA2, comparing to CZA1 (0.39 mL/g in pore volume, 8.6 nm in pore radius) with amorphous Al2O3 and those reported CZA materials, is associated with the morphology (nanorods and nanofibers) and stacking of primary particles. In addition, results of XRD and XPS manifest that the superior reducibility of CZA2 is associated with the homogenous CZ structure and the resulting increased surface oxygen vacancies. Then these vacancies maintain the smaller PdO crystal size and higher fraction of Pd2+ in the thermal treatment due to the increased metal-support interaction between CZA2 and Pd species. As a result, Pd/CZA2-a could keep a better three-way catalytic activity.