| NOx and soot are the main pollutants in diesel emission. How to enhance soot combustion at low temperature and improve NOx reduction efficiency is crucial to the elimination of diesel emission. So, it is necessary to develop highly active catalysts with not only oxidation active sites but also reductive active sites used for the simultaneous removal of NOx and soot. In this dissertation, several series of Co- and Ni-based perovskite-type complex oxides are selected, synthesized and employed to the simultaneous NOx-soot removal. The A-site cations of perovskite were partially substituted by alkali metal ions, such as Li+, Na+, K+, Rb+; and the B-site cations were also partially replaced by transition metal elements, such as Fe, Ni and Cu. The substitution effects on the structures and catalytic performance of the catalysts were systematically investigated, and the substitution amounts were also optimized. On the basis of the characterization of in situ DRIFT, XPS, TPD/TPR, etc., the C-NO-O2 reaction pathway was proposed.Firstly, Fe-substituted La0.9K0.1Co1-xFexO3-δperovskite-type catalysts were successfully synthesized by citric acid complexation method. The effects of Fe-substitution amount on the catalytic activities of soot combustion, NOx storage and simultaneous NOx-soot removal were carefully investigated. The size of prepared catalysts is between 40 and 80 nm, falling in the same order of magnitude as soot particulates, making them possibly possess the highest specific number of contact points between the two counterparts. The introduction of Fe in B-site enhances the soot oxidation ability, NOx storage capacities and simultaneous NOx-soot removal efficiency, showing an optimal Fe-substitution amount of 10%. The improved catalytic activities of Fe-substituted catalysts originate from the relative higher content and better mobility of lattice oxygen, and the larger amount of generated oxygen vacancies. These oxygen vacancies can adsorb and activate NO and/or O2 molecules, providing active oxygen species for NO oxidation and soot combustion. In addition, the existence of some high valence Fe ions (Fe4+) is favorable to the transformation of NO to NO2, facilitating the reaction between NOx and soot.The K and Ni simultaneously substituted La1-xKxCo1-yNiyO3-δperovskite catalysts were also prepared by the same method. The influence of different substitution conditions on the structure and catalytic performance of the perovskites was studied. It is found that K and Ni simultaneously substituted catalysts can lower soot combustion temperature and the activation energy of soot oxidation reaction significantly, and largely improve NOx storage capacities and NOx-soot reduction efficiency, however, the Ni amount seems to have little effect on the activities. Simultaneous incorporation of K and Ni into LaCoO3 enhances the redox properties of the catalysts, and thus facilitating redox reaction. Weakly chemisorbed surface species is the active oxygen species for NOx-soot reaction, which can be increased by introduction of K, especially the simultaneous introduction of K and Ni. Moreover, a large amount of oxygen vacancies were generated after the simultaneous substitution. On one hand, the oxygen vacancies can adsorb/activate NO, enhancing the NOx storage ability of the catalysts; on the other hand, the oxygen vacancies can adsorb/dissociate gaseous O2, maintaining the adsorbed oxygen species continuous regeneration, facilitating the transferring of oxygen species during the NOx-soot reaction. At last, K and Ni simultaneous substituted catalysts possess the largest amount of Co4+, which shows better oxidation ability, and thus promoting the transformation of NO to NO2 and soot oxidation.By incorporation of K and Cu into LaCoO3 perovskite, La1-xKxCo1-yCuyO3-δcatalysts were thus obtained. After introduction of K and Cu, the reducibility of the catalysts was improved; the content of weakly chemisorbed surface active oxygen species (O2-, O-) was increased and the mobility of O2- and O- was also enhanced; some of the Co3+ were transformed into Co4+, which facilitated the formation of NO2, at the same time, a large amount of oxygen vacancies were also generated, the formed oxygen vacancies can adsorb and dissociate gaseous O2, maintaining the continuous regeneration of O2- and O- species, and also promoting the mobility of O2- and O- towards soot during NOx-soot reaction. These factors lowered soot oxidation temperature and the reaction activation energy, and also improved NOx storage ability and simultaneous NOx-soot reduction efficiency. According to the results of in situ DRIFT, NOx mainly adsorbed as monodentate and bidentate nitrates on the surface of catalysts at low temperature, and stored as ionic nitrates in the bulk structure of the catalysts at high temperature. Based on the above results and analysis, a potential reaction mechanism of simultaneous NOx-soot removal was proposed.Moreover, a series of LaNiO3 perovskites with A-site cations partially substituted by alkali metal ions, such as Li+, Na+, K+ and Rb+, were also prepared and investigated. With the atomic number of the doped alkali metals increasing, soot oxidation temperature and activation energy of the reaction was decreased gradually, and NOx storage capacities and NOx-soot reduction efficiency were enhanced gradually, too. The alkalinity of the substituted alkali metals increases with the atomic number increasing, which facilitates the NOx storage and reduction. The substitution makes the catalysts have better reducibility, which is favorable to redox reaction. After substitution, a large number of weakly chemisorbed surface active oxygen species (O2-, O-) were generated, O- species may have participated in the NOx-soot reaction; at the same time, lots of oxygen vacancies were also formed.The substitution effect of K on the catalytic performance of soot combustion, NOx storage and simultaneous removal of NOx and soot was further investigated. When La3+ was partially replaced by K+, the catalytic activity was enhanced further, and the activities exhibit a typical volcano tendency with the K-substitution amount increasing, the optimal substitution amount is 10%. Introduction of K into LaNiO3 catalyst improved the reducibility and the content of surface O2- and O- species, which is the active oxygen species for NOx-soot reaction. Meanwhile, large amounts of oxygen vacancies were also generated, which facilitate adsorption/activation of NO and oxygen species.Finally, the LaNiO3 perovskites with A-site ions partially substituted by Rb were also prepared. It is found that Rb-substitution lowered soot combustion temperature, and enhanced NOx storage capacities and NOx-soot reduction efficiency. With the Rb-substitution amount increasing, the catalytic activities displayed a typical volcano tendency. Through the investigation of reaction pathways, two kinds of reaction mechanisms are identified for soot combustion. The first one is oxygen spillover mechanism, namely, gaseous O2 adsorbs and dissociates on the oxygen vacancies of the perovskite catalysts, and forms weakly chemisorbed surface active oxygen species (O2-, O-), which can actively react with soot particulates, giving out CO2; the second one is the NOx-aided gas-phase mechanism, that is, NO is oxidized to NO2 on the catalyst at first, then soot reacts with as-formed NO2 in the presence of O2. The NOx storage and reduction by soot follow nitrates pathway.
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