A Study On N₂O Catalytic Decomposition Over Nickel-based Composite Oxides

In recent years, the emissions of nitrous oxide (N2O) from production processes of nitric acid and adipic acid increase year by year. N2O is not only a greenhouse gas which has a high global warming potential (GWP=310) but also largely contributes to the stratospheric ozone destruction. Therefore, it is urgent to eliminate the N2O. Catalytic decomposing N2O to N2 and O2 has been recognized as the most prospective method for elimination pollution derived from N2O. Since some interference gases (such as H2O and O2) are co-existed with N2O, all the factors including the cost, the activity at low temperature and the activity resisting to O2 and H2O under the reaction conditions should be taken into account for the catalyst screening.In the present thesis, series of BaxNi9, CeyNi9 and CeyBa1.5Ni9 catalysts were prepared by co-precipitation method and tested for the reaction with different feed gas composition. The results showed that both Ba and Ce could improve the catalytic activity of NiO. By optimizing the doping ratio of Ba or Ce to NiO, Ba1.5Ni9 and Ce1.0Ni9 as the most active catalyst samples for the reaction in the BaxNi9 and CeyNi9 samples, respectively, became noticeable. Moreover, NiO co-modified by Ba and Ce exhibited much higher activity than that modified by single one of them for the reaction. When Ba and Ce were co-existed with NiO in the mole ratio of Ce:Ba:Ni=1.0:1.5:9, catalytic activity of the catalyst was the best in the CeyBa1.5Ni9 samples. Meanwhile, the influence of preparation method on catalytic activity of catalysts was investigated. It was found that the catalytic activity of Ni-based catalysts prepared by co-precipitation method was much higher than that by citric acid method. Some techniques, such as BET, XRD, H2-TPR, O2-TPD and XPS, were applied to characterize the structure and chemical properties of these catalysts, with which the following conclusions was obtained:Appropriate amount of Ba exsting in the catalysts greatly weakened the Ni-O band, while that of Ce significantly restrained the crystal growth of NiO during the preparation and hence increased the surface area of catalysts. Moreover, the co-existence of Ba and Ce in Ni-based catalysts exhibited a remarkable synergic effect on the catalytic activity for the reaction. Due to the synergic effect that Ce primarily served a function of accelerating the dissociation of N2O, and Ba played a role of facilitating the O2 desorption from the active sites, the Ce1.0Ba1.5Ni9 catalyst had more active sites and a better O2-resistance ability than NiO, Ba1.5Ni9, and Cei.oNig catalysts. The influence of Co on the catalytic activity of NiO and Ba1.5Ni9 for N2O decomposition catalysts was also investigated in this thesis. Different series of CoxNi9 and CoxBa1.5Ni9 catalysts by co-precipitation method were prepared, and tested for the N2O catalytic decomposition. It was found that Co could improve the catalytic activity of NiO in the presence of BaCO3 while showed an opposite role in the absence of BaCO3. By a series of techniques characterizing the structure and chemical properties of these catalysts, it was found that Co strengthened the Ni-O bond and decreased the surface area when added into pure NiO without BaCO3, while in the presence of BaCO3, it dramatically increased the surface area and amount of active sites of NiO.