Study On Low-Temperature Denitrification Properties Of Modified Activated Carbon-Load Copper-Based Catalyst

Nitrogen oxide(NOx),one of the components of air pollution,is mainly produced by human activities in production and living,which harms the environment and human health.Selective catalytic reduction(SCR)is mostly used for denitration in industry.However,commercial catalysts commonly used have high operating temperature and narrow activity window,so flue gas temperature fluctuation can easily make catalysts ineffective.Therefore,in recent years,low temperature SCR catalyst is the focus of research,in addition,its sulfur and water resistance performance is the key of SCRcatalyst.In this paper,the activated carbon was modified to be the best carrier.Secondly,a series of Cu/AC catalysts were prepared using Cu as active component and modified activated carbon as support.The denitration performance,resistance and reaction mechanism of Cu/AC catalysts at low temperature were systematically studied.Finally,Cu/AC catalyst was loaded Ce.The effects of Ce doping of the catalyst were investigated.The physicochemical properties of the catalyst and the poisoning reason of the catalyst were analyzed by different test methods,reaction mechanism was speculated.The main conclusions are as follows:(1)The selected activated carbon was first modified by 20%nitric acid and then roasted by microwave.The BET,FTIR and Boehm titration characterization showed that the specific surface area of AC increased by 51.7%and the total amount of oxygen-containing functional groups increased by 89.6%after nitric acid modification,which was the best modification method.The modified activated carbon could further expand the pore volume and increase the surface functional groups containing oxygen and nitrogen when roasted at 300℃ in a microwave tube furnace.(2)The optimal parameters of Cu/AC catalyst are as follows:Cu loading amount of 16%,130℃,space velocity 6000 h-1,urea loading 10%.At this point,the initial NO conversion rate was 100%,and the penetration time was 190 min when the denitration efficiency drops to 75%.The results of sulfur and water resistance experiments showed that SO2 caused the formation of sulfate on the surface of the catalyst,which resulted in serious deactivation,and the denitration efficiency and penetration time decreased sharply.The presence of water vapor decreased the denitration efficiency,but did not deactivate the catalyst.(3)The results of SEM and EDS showed that when the weight fraction of copper was 16%,the distribution of copper oxide in the pore of activated carbon was relatively uniform,but there is agglomeration phenomenon exiists.H2-TPR characterization results showed that the oxygen and nitrogen functional groups in copper oxide and activated carbon were reductive.XPS results showed that CuO and Cu2O characteristic peaks were observed at 932.7 eV and 933.2 eV,respectively.The reaction mechanism analysis showed that NO was first adsorbed into adsorbed state,and then oxidized to NO+ads by Cu2+,and then reduced to N2 by reaction with urea or ammonia.The ammonia was produced by hydrolysis of urea,and the whole process was a cycle of Cu+ and Cu2+,which continuously provided electrons to reduce NO.(4)The penetration time of 16%Cu/AC catalyst supported by 8%Ce increased from 190 min to 490 min;The denitration efficiency of single component cerium loading was low,and the penetration time was only 16 min,so Ce was used as catalyst assistant.In the resistance experiment,the activity of 8%Ce/16%Cu/AC catalyst decreased,but the decline rate was significantly less than that of 16%Cu/AC catalyst,indicating that the doping of Ce could inhibit the reaction of SO2 between urea and CuOx to generate sulfate substances.(5)H2-TPR results showed that the reduction peak of Ce doped copper oxide moved to the low temperature region,indicating that the low temperature catalytic activity of the active component copper was enhanced.XPS characterization results showed that the oxides of cerium were CeO2 and Ce2O3.The presence of lattice oxygen and adsorbed oxygen in O peak was helpful to improve the catalytic performance.(6)The reaction mechanism of Ce doping is speculated that:Ce3+and Ce4+constantly gain around copper oxide,which helped Cu+ and Cu2+ fast conversion,copper oxide active components in the transformation accelerate reaction rate of NO and urea,and thus progress decreased reaction activation energy,improved the activity of catalyst,and increased ability to resist water and sulfur.