Moderating the interaction among Pd, CeO2, and Al2O3 for improved three-way catalysts.

Abstract

The Pd distribution and the CeO2-Al2O3 combination are among the decisive factors for the performance of commercial three-way catalysts. Generally, the sufficient doping of Pd into ceria-based oxides and the intimate interaction between CeO2 and Al2O3 could both benefit the three-way catalytic reactions. However, in the present work, the moderate doping of Pd into CeO2 and less intimate CeO2-Al2O3 interaction were found to be responsible for the much higher catalytic activity (the decrease in T50 was 52, 119, or 55 °C for C3H6, CO, or NO) in PdCe/Al2O3-CP than PdCe/Al2O3-Imp, for which the Pd and Ce species were co-loaded onto Al2O3 through the co-precipitation or impregnation method, respectively. It was intriguing to find that the co-precipitated PdCeOx in PdCe/Al2O3-CP showed less sufficient doping of Pd into CeO2 than the co-impregnated PdCeOx in PdCe/Al2O3-Imp; as a result, both a higher fraction of highly active metallic Pd and a higher Pd dispersion were realized in PdCe/Al2O3-CP. Moreover, due to the less intimate CeO2-Al2O3 interaction, specifically the less severe penetration of the Pd and Ce species into Al2O3, PdCe/Al2O3-CP showed higher Pd dispersion, specific surface area, pore volume and size than PdCe/Al2O3-Imp. The presence of more abundant reactive Pd0, and the higher accessibility of the active Pd and CeO2 sites, together with improved redox properties and enriched oxygen vacancies contributed much to the enhanced three-way catalytic activity of PdCe/Al2O3-CP. Additionally, simultaneously optimizing the Pd distribution and the CeO2-Al2O3 combination in a single step, as reported in this work, is also highly desirable in industry.