Optimized synthesis of highly thermal stable CeO2-ZrO2/Al2O3 composite for improved Pd-only three-way catalyst

Abstract

As is well known, impregnation of precursors of Ce and Zr onto as-prepared Al2O3 powders is a commonly used approach to prepare CeO2-ZrO2/Al2O3 composite. In this work, a highly thermal stable CeO2-ZrO2/Al2O3 composite was synthesized by modifying the conventional preparation procedure, i.e., the precursor of Al2O3 thermal treated at comparatively lower temperature (200°C) was applied to conduct the impregnation process. The characterization results of the supported Pd-only three-way catalysts reveal that in the modified sample, stronger interaction between CeO2-ZrO2 and Al2O3 is achieved, which consequently gives rise to higher thermal stability of the catalyst. Upon hydrothermal aging treatment, only slight aggregation of the CeO2-ZrO2 and Al2O3 particles takes place, meanwhile phase transformation of γ-Al2O3 and phase separation of CeO2-ZrO2 component are successfully suppressed. As a consequence, Pd species supported on the modified CeO2-ZrO2/Al2O3 composite remain finely dispersed, and more oxidative PdO species are maintained owing to the intimate interaction between Pd and CeO2-ZrO2. Therefore, improved reduction capability and superior three-way catalytic performance are achieved for the modified Pd/CeO2-ZrO2/Al2O3 catalyst after aging treatment.