| The catalytic abatement of NOx from flue gases,including selective catalytic reduction(SCR)and decomposition of NOx,is an important commercial process in environmental catalysis.Low hydrocarbon(≤C3)as redutant has attracted particular interest in SCR of NOx,since low hydrocarbon is the main component of natural gas. The catalytic decomposition of NOx represents the simplest and most attractive solution for NOx removal,since it does not involve the addition of reductants and only N2 and O2 are formed.However,the catalysts used in the HC-SCR and decomposition of NOx reaction are sensitive to the reaction conditions(such as SO2,H2O,GHSV and so on). Recently,extensive efforts have been made to improve the activity of these catalysts. For the above consideration,we investigated the effects of second additives on Ag/Al2O3,Co/H-beta,and Fe/H-beta catalysts respectively in this dissertation.The effect of MgO addition on SO2 and water tolerance of Ag/Al2O3 for CH4-SCR was investigated at low temperature(573～673 K);The influence of Zn addition on the activity of Co/H-beta for C3H8-SCR was studied at high GHSV;The catalytic performance and physico-chemical characteristics of Fe-Mn/H-beta in low-temperature decomposition of NOx in excess of oxygen were carried out.The main original conclusions of this work are drawn:1.MgO addition significantly promotes the SO2 and water resistance of Ag/Al2O3 for CH4-SCR at low temperature range of 573～673 K.Only five percent decrease of NOx conversion happened in the presence of 100ppmSO2 and 15%H2O.The slight decrease in catalytic activity over Ag/MgAl2O4 exposure to SO2 is attributed to the partially deactivation of alumina sites poisoned by SO2.MgO may effectively inhibit the competitive adsorption between NOx and SO2 in alumina sites,and enhances SO2 adsorption on the magnesia surface.The silver oxide particles were well dispersed and large silver crystals were present in Ag/MgAl2O4 catalysts.The apparent activation energy of CH4-SCR reaction over Ag/MgAl2O4 is equal to 94.6kJ/mol,which is lower than that of other catalysts. 2.The NOx conversion about 95%over 2%Co-2%Zn/H-beta is reached in C3H8-SCR at 723K and high GHSV of 20000 h-1.Co-Zn/H-beta catalyst exhibited high activity at high GHSV range of 10000～100000h-1,which 70%NOx conversion was obtained at GHSV of 100000h-1.When the concentration of SO2 is less than 200ppm,the activity of Co-Zn/H-beta catalyst was little inhibited by SO2,and NOx conversion decreases 5%. The competitive adsorption between NOx and SO2 in active sites was not serious. However,the activity of Co-Zn/H-beta catalyst was greatly inhibited in the presence of high concentration of SO2(≥400ppm),due to the obvious competitive adsorption between NOx and SO2 in active sites.The NOx conversion declines about 30%.There exists a cooperative effect among the Zn and Co in Co-Zn/H-beta.The oxidation of C3H8 is inhibited effectively by Zn,and NO oxidation to NO2 is enhanced by Co. Addition of Zn(less than 2%)could inhibit the formation of CoAl2O4,which results in more active site of Co.3.Fe-Mn/H-beta shows high activity for low-temperature decomposition of NOx in the presence of oxygen.The coexistence of manganese and iron enhances the dispersion and lowers the crystallinity of both metal oxides.5%Fe-5%Mn/H-beta exhibits the highest activity among Fe-Mn/H-beta catalysts with Mn/Fe=1.Neither O2 nor CO2 inhibition was observed in NOx decomposition over Fe-Mn/H-beta.
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