Study Of Ru-Based Supported Catalysts For Selective Catalytic Reduction Of NO_x By CO At Oxygen-rich Conditions

Nitrogen oxides(NOx),sulfur oxides(SOx)and carbon dioxides(CO2)are three major pollutants being dangerous to air environment.Among them,CO2 emission control is mainly achieved by energy conservation and developing new energy,meanwhile desulfurization technologies become more and more readily in practical application and nowadays attain superior removal effects.Denitration technologies have attracted much attention and still been investigated extensively,among which selective catalytic reduction(SCR)technology is considered to be the mainly efficient method,whilst NH3-SCR exists many defects,such as ammonia leakage and equipment corrision.So,in the present thesis,CO existed in the flue gas is selected as the reductant and is used to selective cataltic reduction of NOx under oxygen-rich condition,to simultaneously removal CO and NO.The research goal of the thesis is therefore to design a catalyst with high activity for CO-SCR of NOx in oxygen-rich atmosphere.A series of supported Ru-based bimetallic or multi-metallic catalysts were designed in the thesis,and its activity,characteristics and active center were investigated under enriched oxygen condition.The main contents are displayed as follows:Firstly,the Ru/Al2O3,Ag/Al2O3 and bimetallic Ru-Ag/Al2O3 catalysts were prepared by the incipient-wetness impregnation method,and the denitrification activity was studied under the condition of excess oxygen.It was found that the activity of bimetallic Ru-Ag/Al2O3 catalysts was greatly improved compared to single metal catalysts,and the conversion of NOx could reach 65.7%in the range of 300 to 400 °C.Secondly,the preparation conditions and reaction conditions of Ru-Ag/Al2O3 catalyst were further optimized,and the optimum activity conditions were determined:two-step impregnation method,impregnation of Ru first followed by impregnation of Ag,Ru loading 0.5 wt.%,Ag loading 5 wt.%,calcination temperature 600°C,O2 content 0.5 vol.%,space velocity 37,500 h-1.At the same time,the catalyst has good regeneration performance,stability and water resistance.Thirdly,the microstructure and physico-chemical properties of the catalyst were characterized by N2 adsorption and desorption,SEM,XRD,UV-vis,NO-TPD and XPS.It was found that the active components of the catalyst were mainly Ru0 and Ag0,when Ru and Ag at the optimum loading,Ag0 and Ag+,Ru0 and Ru4+ may reach the optimum ratio after reduction treatment,reaching the best activity.Finally,in order to further modify the Ru-Ag/Al2O3 catalyst,another non-precious metal was substituted for Ag in terms of cost,and it was found that the NOx conversion of 0.5Ru5Ba/Al2O3 at the space velocity of 18750 h-1 was 78.5%.In terms of activity,adding the third component as additive,compared with Ce,La,Mg,and Ba,the highest NOx conversion of 74.90%was found for the 0.5Ru-5Ag5Ba/Al2O3 catalyst at the space velocity of 37,500 h-1,which greatly widened the temperature range of catalyst.