Preparation And Performance Of Copper And Iron Based Metal Oxide Catalysts For Highly Effective Selective Catalytic Reduction?CSR? Of No With NH₃ At Low Temperature

Nitrogen oxides(NO,NO2,and N2O)are the major contributors to air pollution and are mainly emitted to the atmosphere through fixed resources such as thermal power plants and diesel engines.At present,the removal of nitrogen oxides from the atmosphere has become a challenging task worldwide.Recently,selective catalytic reduction with ammonia(NH3-SCR)has been considered as the most effective,most urgent,promising and commercialized technology for controlling NOx.Commercial V2O5-WO3(Mo O3)-Ti O2 catalysts are widely used in the large power plants.However,there are still some shortcomings,which constrain their usage for nonelectric plant such as the biological toxicity of V2O5 to human being and eco-environment,narrow NH3-SCR reaction temperature range of 300-400 °C,and unselective oxidation of NH3 to produce N2 O at high temperature.Furthermore,the temperature of exhaust smoke NOx emitted from stationary resources such as industrial boiler,coal-fired power plants,cooker heater,combustion furnaces,industrial boiler and glass melting stove,is below 300 °C in general.The conventional V2O5-WO3(Mo O3)-Ti O2 catalyst is not effective for above exhaust smoke NOx.Therefore,the development of a novel NH3-SCR catalyst with excellent low temperature NO conversion,high N2 selectivity and wide reaction temperature window is very important and has theoretical and practical significance.Transitional metal oxides such as copper and iron based oxides are considered to be promising NH3-SCR denitrification catalysts.In this thesis,copper and iron were selected as the main active components of the catalysts,and the different metals(Ce,Nb and Zr)were added to modify the catalytic performance.A series of Cux-Ce0.5-x-Zr0.5(x = 0.1-0.5),Cux-Nb1.1-x(x = 0.45,0.35,0.25,0.15)and Fex-Nb0.5-x-Ce0.5(x = 0.45,0.4,0.35)oxide catalysts were prepared by adjusting the ratio of metal oxides for NH3-SCR reaction at low temperature of NO.Various characterization methods such as Raman,XRD,TEM,H2-TPR,NO-TPD,NH3-TPD,XPS and in situ DRIFTS were used to explore the synergic effects of various metal oxides on the structure and activity of the catalysts.Moreover,the corresponding NH3-SCR denitrification reaction process was proposed based on the characterization results.The Cux-Ce0.5-x-Zr0.5 oxides catalysts with different Cu/Ce ratio(Cux-Ce0.5-x-Zr0.5(x = 0.1-0.5))were synthesized.The synergistic effects between copper and cerium on the catalytic performance of Cux-Ce0.5-x-Zr0.5 for selective catalytic reduction of NO with ammonia were investigated by various characterization methods.It was found that the Cu0.2-Ce0.3-Zr0.5 catalyst showed the excellent SCR activity,N2 selectivity and H2O/SO2 durability in the low temperature range of 150-270 oC even at high gas hourly space velocity of 84,000h-1.The strong interaction leads to the improvement of the acidity and the increase in the amount of active oxygen species(oxygen vacancy),which are responsible for the higher activity at low temperature.The DRIFTS results indicate that abundant ionic NH4+(Br?nsted acid sites),coordinated NH3 on the Lewis acid sites,as well as highly active monodentate nitrate and bridging nitrate species were the key intermediates in the SCR reaction.The Cux-Nb1.1-x(x = 0.45,0.35,0.25,0.15)bimetal oxides catalysts were prepared in order to increase the NH3-SCR activity window of the Cu based catalysts.The correlations among the catalytic performances,the acid/redox properties and the structures of the binary oxides systems were explored through different characterization techniques.The characterization results point out that the ratio of Cu to Nb has great influence on the activity of NH3-SCR reaction.Different catalytic activities of CuxNb1.1-x(x = 0.45,0.35,0.25,0.15)mixed oxides could be attributed mainly to surface area,acid amount,the adsorption and activation of NH3 and redox ability of the catalysts.Among these Cux-Nb1.1-x(x = 0.45,0.35,0.25,0.15)oxides catalysts,the Cu0.25-Nb0.85 catalyst exhibited the complete NO conversion in the reaction temperature range of 180-330 °C,together with near 100% N2 selectivity and remarkable SO2/H2 O resistance.Moreover,the Cu0.25-Nb0.85 catalyst still exhibited wide activity temperature window of 185-380 °C even in the presence of 5% H2 O under GHSV of 70,000 h-1.A series of Fex-Nb0.5-x-Ce0.5(x = 0.45,0.4,0.35)oxides catalysts were also prepared to obtain the catalyst with excellent NH3-SCR activity and selectivity at low and high temperature.The Fe0.4-Nb0.1-Ce0.5 exhibited above 90% NO conversion in the range of 180-400 oC,together with near 100% N2 selectivity.The characterization results point out that the excellent catalytic performance of Fe0.4-Nb0.1-Ce0.5 can be ascribed to the strong interaction among Nb,Fe and Ce oxides.The strong interaction not only increases the BET surface area and redox ability of the catalyst,but also significantly improves the acid amount leading to the enhancement of the adsorption and activation of NH3,which is advantage of the reactivity of adsorbed nitrate together with the adsorbed NH3 species.