Preparation Of Cu-Mn Oxides And Its Performance On The Selective Catalytic Oxidation Of Ammonia

Ammonia (NH3) is one of typical toxic waste gas and does serious harm to toecological environmentand human health. Therefore, controlling and eliminatingammonia pollutionarouse widespread attention.Selective catalytic oxidation of ammonia (NH3-SCO) is an efficient and no secondary pollution method. And the key of SCO technology is catalyst. At present, noble mental catalysts have a superior low-temperature catalytic performance but withpoor N2 selectivity. Transition mental catalysts due to their low price and good performance of catalytic oxidation are remarkable. Among them, manganese oxides show a favourable low-temperature catalytic performance, but the N2 selectivity is too low. However, copper oxides exhibit good N2 selectivity. So in this thesis, Cu-Mn oxides prepared by various methodsand the effect of different Cu loadings were measured. Furthermore, the relationship between the structure and the activities was built through investigating the performance of catalysts. The main contents of the work are as follows:(1) The MnO2 catalyst was prepared by urea-assisted hydrothermal method and its ammonia catalytic activity was measured. The results showed thatwhen the ratio was n(Urea)/n(Mn)=10:1, the MnO2 catalyst calcined with 400? for 6 hshowed an excellent catalytic activity for ammonia oxidation with complete conversion temperature of 170?. However, the N2 selectivity was only 60%. To enhance the N2 selectivity of the catalytst, the Cu-Mn oxides catalysts were prepared by impregnation, precipitation and hydrothermalmethod and their ammonia catalytic activity was measured. The results showed that the Cu-Mn oxides synthesized by hydrothermal method exhibited the best ammonia catalytic activity with 100% NH3 conversion at 170?. Moreover, the N2 selectivity was increased to 80%.(2) The effect of Cu loading on the activity was investigated. When the Cu loading was 1 wt%, the Cu-Mn oxides showed the best activity. The NH3 conversion was enhanced 17% in the range from 80? to 140? contrast to the other catalysts. Moreover, the catalyst showed the highest N2 selectivityof above 80%. Meanwhile, the catalyst with the 1 wt% Cu loadingmaintained NH3 conversion above 98% during 25 hours(T=170?). The catalyst still had the complete conversion temperature of 170? after cycle test forthree times. When the Cu loading was less than 3 w%, Cu species were highly dispersed on the surface of MnO2. While the loadingwas increased to 5 wt%, the diffraction peak of MnO2 got narrow, which reduced the catalytic activity.(3) The results of temperature programmed desorption of ammonia and temperature-programmed surface reaction techniqueshowed thatthe Cu-Mn oxides loaded with 1 wt% Cu had the strongest adsorption ability. With the increase of Cu, the desorption temperature of catalyst became higher. H2 was detected with the desorption of NH3, which explained that the ammonia was activated toform the intermediates NHx. N2O species was also detected. Therefore, N2 selectivity could be related to the production of N2P.