Preparation Of SCR Catalyst Supported On Attapulgite And Its Performance Of Denitrification And Mercury Removal

The nitrogen oxides and elemental mercury in the atmosphere come mainly from coal-fired flue gas.In recent years,the control of nitrogen oxides and elemental mercury in coal-fired flue gas has become a hot research topic.The process of denitrification and mercury removal in industry is often carried out in different equipment,which increases the operation cost.Among many simultaneous denitrification and mercury removal technologies,selective catalytic reduction(SCR)technology is more studied.However,the commonly used SCR catalysts have some disadvantages such as high operating temperature and high cost.It is necessary to develop low-cost and high-activity SCR catalysts for denitrification and mercury removal.Attapulgite(ATP)has the advantages of large specific surface area,good adsorption performance and low price.Instead of titanium oxide and carbon-based carrier with relatively high price,it can effectively reduce the cost of the catalyst while ensuring its low-temperature activity.SnO2-Fe2O3/ATP catalysts were prepared,and their properties of denitrification and mercury removal were investigated.The results showed that the interaction between the active components of the catalyst was enhanced when SnO2 and Fe2O3 were loaded at the same time.The interaction resulted in the decrease of the active component particles and the increase of dispersion,which is beneficial to the improvement of the catalytic activity.The denitrification activity window of the catalyst was broadened with the addition of SnO2.The highest catalytic activity was observed when Sn:Fe is 1:2.The conversion of NO remained above 89.4%and the mercury removal efficiency kept above 78.1%at range from 160 to 240?.The results of sulfur resistance test showed that SO2 can obvious inhibit the denitration performance and slight promote the removal of mercury.CeO2 has strong ability of storing and releasing oxygen,CeO2/ATP was prepared by ultrasonic impregnation method and its performance of denitrification and mercury removal was investigated.The structural characterization of the catalyst showed that the specific surface area of 10%-CeO2/ATP was the largest,which improved its adsorption performance.When the space velocity is 40000 h-1 and the catalytic temperature is 200 ? the denitrification rate and mercury removal rate can reach 89.6%and 92.4%,respectively.However,the addition of SO2 has an inhibitory effect on the denitrification and mercury removal performance of the catalyst.In order to improve the denitrification rate of CeO2/ATP,CeO2-CeVO4/ATP with different CeO2 loadings were prepared by ultrasonic impregnation method and sol-gel method,and their activities of denitrification and mercury removal were investigated.The results of structural characterization showed that the catalysts prepared by sol-gel method have larger specific surface area,pore volume,Ce3+/Ce4+ and chemisorbed oxygen than the catalysts prepared by impregnation method.The catalysts prepared by sol-gel method has high activity of denitrification and mercury removal,and CeO2(0.1)-CeVO4/ATP has the best performance.The conversion of NO and the mercury removal rate were above 94.5%and 90.5%in the temperature range of 160 ? and 220 ? respectively.In addition,the catalyst has strong resistance to sulfur poisoning.Even with the presence of 1000ppm SO2,the denitrification rate and mercury removal rate of the catalyst can still reach78.7%and 90.4%at 180?.In order to further improve the sulfur resistance of the catalyst,the low temperature SCR catalysts CeO2/TiO2-ATP with different TiO2/ATP ratios were prepared by sol-gel method,considering that the titanium-based SCR catalysts have better sulfur-resistance properties.The catalyst was modified by low temperature plasma.The results showed that the modification of the catalyst by low temperature plasma not only alleviated the agglomeration of the catalyst surface,and improved the dispersion of CeO2on the surface of the catalyst,but also promoted the reduction of Ce4+ on the catalyst surface to Ce3+,and more chemisorbed oxygen was generated,which enhanced the performance of catalyst for denitrification and mercury removal.When TiO2/ATP was 1:3,the catalyst has a higher efficiency of denitrification and mercury removal under the conditions of 2%O2 and NH3/NO=1.The conversion of NO remained above 93.3%and the mercury removal efficiency remained above 86,7%at range from 180 to 240 ?.At the same time,the catalyst has a strong anti-sulfur ability,the denitrification efficiency of the catalyst reached 83.9%,and the efficiency of mercury removal reached86.8%at220?,even with the presence of 1000ppm SO2.