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

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 T-50 was 52, 119, or 55 degrees 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 Pd-0, 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.