Chen Zhou,Yexin Zhang,Lingjun Hu,Hongfeng Yin,Wei Guo Wang
Mn-doped La 0.8 Sr 0.2 CoO 3 perovskite oxides (La 0.8 Sr 0.2 Co 1– x Mn x O 3 ; x = 0, 0.1, 0.3, 0.5) were synthesized by a modified sol-gel method. The phase-pure oxides were obtained. CoO and carbonates were formed on the surface of La 0.8 Sr 0.2 CoO 3 . With increasing doping content, these impurities were reduced while the stability of the perovskite structure was improved. The valence state of B-site ions and the amount of absorbed oxygen were influenced by Mn doping. The catalytic activity of the perovskite catalysts was investigated for CO oxidation and simultaneous removal of CO, C 3 H 8 , and NO. For CO and NO removal, La 0.8 Sr 0.2 Co 0.9 Mn 0.1 O 3 exhibited the best performance. For C 3 H 8 removal, the reactivity was promoted linearly with the doping content. The structure-activity relationship is also discussed.
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.
Three-way catalysis represents a pivotal technology for converting automobile exhaust pollutants into non-toxic gases. Substituting some noble metals with transition metals is considered a promising way to reduce catalyst costs. Herein, we have investigated the catalytic potential of different configurations of Pd-Cu catalysts prepared by impregnation (PdCu/MA), sol-gel (PdCu-MA), impregnation with physical mixing (Pd/Cu/MA) and sol-gel with physical mixing (Pd/Cu-MA) to modify the interaction of Pd/Cu and MgAl1.82Ce0.18O4 (MA) spinel in this comparative study. The different structures in these catalysts lead to different catalytic performances. PdCu/MA exhibits the best three-way catalytic performance, which owe to the small-sized PdCu particles with high Pd2+ content (45.3%) and optimal interaction of Pd/Cu particles and MgAl1.82Ce0.18O4 support. Furthermore, comprehensive CO-DRIFTS, H2-TPR, and O2-TPD analyses discover that the metal-support interaction is beneficial to enhance the catalytic performance in three-way catalysis. Overall, we demonstrated that the interaction between PdCu bimetals and support can regulate the electronic state of Pd, thereby enhancing the use and efficiency of noble metals.
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