| In recent years, the emissions of nitrous oxide (N2O) from nitric acid and adipic acid production as well as motor vehicle exhaust are increasing year by year. N2O not only the main greenhouse gas, but also takes part in the depletion of stratospheric ozone. Therefore, it is urgently required to eliminate the N2O from industrial exhausts. Among the methods for N2O elimination, catalytic decomposition of N2O is the most promising method. The temperature for the exhausts coming from the vehicle engines and tail gases being resulted from nitric acid and adipic acid production are not high enough. In addition, several kinds of impurities such as CO2, H2O, O2, SO2, NO exist in them along with N2O and N2. Therefore, developing a catalyst with good resistance to the impurities and a better catalytic performance at low temperature is a significant challenge work in this field.In this thesis, a series of NxCo (N=Bi, Pb, Sn, Sb; x=N/Co) mixed oxide catalysts were prepared by co-precipitation method and tested for the N2O catalytic decomposition. It was found that Bi and Pb significantly improve the activity of Co3O4 catalyst. On this basis, the composition of the catalysts was optimized, which indicats the x to be 0.02 and 0.04 for the BixCo and PbxCo, respectively. Both of the Bi0.02Co and Pb0.04Co catalysts have performed good catalytic activity for the N2O decomposition in the presence of 10% CO2. Outstandingly, the activity of Bio.o2Co catalyst was almost not influenced by CO2, while that of Pb0.04Co influenced by the CO2 was quite limited. Under the reaction conditions of 2000 ppm N2O+ 10% CO2+Ar and GHSV=20000 h-1,N2O conversion reached 95% over the Bi0.02Co catalyst at 400℃, while that even reached 100% over the Pb0.04Co catalyst at 350℃.The structure and chemical properties of the catalysts were characterized by BET, XRD H2-TPR, O2-TPD. It was found that Bi and Pb being added to Co3O4 were highly dispersed in the samples, which made the Co3O4 crystal size decreased and hence the surface area of the catalysts increased. However, the structure of Co3O4 in the samples was not changed. The results imply that the Bi and Pb presents at the out side of the Co3O4 crystalites.It was found that oxygen vacancies that were widely accepted as the active site for the reaction to the transitional metal oxide as well as composite metal oxide catalysts, can be formed much more for Bi0.02Co catalyst than the pure Co3O4 catalyst. The mechanism for Bi promoting the reaction was further proved by our N2O pulse reaction experiments, which indicats that the oxygen vacancies on catalyst surface involved in the reaction, and the formation of them is the rate determing step. Bi in the catalyst significantly improving the reaction is just due to accelerating the vacancy formation by facilitating O2 desorption from the catalyst surface.In addition, K modified Bio.o2Co was also investigated for the N2O decomposition. Compared to K0.01Co that was reported to be the most active catalyst for the reaction, K0.01Bi0.02Co catalyst displayed better catalytic performance for the feed gas mixture 2000 ppm N2O+ Ar. However, when CO2 presents in the feed gas, the activity of both K0.01Co and K0.01Bi0.02Co instantly dropped due to the CO32- species formation on the catalyst surface, though the latter still exhibited better than the former. |
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