| The emission of NOx is closely related to environmental issues such as acid rain,photochemical smog and haze.NO is the main form of NOx.The low-temperature removal of NO(<120?)is a difficult and hot point of current research.It is a promising method to remove NO by low temperature adsorption of modified activated carbon.In this paper,commercial coconut shell activated carbon was used as raw material to improve its adsorption performance of NO through chemical modification.The preparation,NO adsorption and regeneration of modified activated carbon(MAC)were systematically studied.Firstly,the low-temperature NO adsorption performance of the MAC was comprehensively compared and evaluated in two aspects:preparation condition(including types of loaded metal oxides,material particle size and different pre-oxidation methods)and NO adsorption condition(adsorption temperature,water vapor and SO2 concentration in simulated flue gas).The commercial coconut shell activated carbon was modified by preoxidition with 300? air,hydrogen peroxide,KMnO4 and HNO3 respectively,then the MAC supported by Mn-Ce-Fe was prepared by co-precipitation method that ammonia hydroxide as the precipitant and Ce(NO3)3·6H2O,Mn(NO3)2·4H2O,Fe(NO)3·9H2O as the precursor.The fixed bed NO adsorption experiment was used to investigate the low temperature adsorption performance of NO.The results show that the load of Mn-Ce-Fe metal oxide significantly improved the NO adsorption capacity of coconut shell activated carbon at low temperature,and the sample with Mn-Ce composite load modification had the best effect.If the particle size of the activated carbon is too large(>0.5mm),it will hinder the internal diffusion of NO in the activated carbon and the load will enter the material.resulting in poor NO adsorption performance of the material.At 55?,different preoxidation treatments further promoted the NO adsorption capacity of Mn-Ce loaded modified activated carbon to different degrees,and the promotion effect is from high to low:HNO3>KMnO4>H2O2?300? air.At 25?,the NO capture rate of sample preoxidized jointly by air and HNO3 was higher than 60%within 13h and the adsorption capacity was 54.4 mg/g.In terms of NO adsorption conditions,as the adsorption temperature increases(55-130?)and the concentration of H2O and SO2 in the simulated flue gas increased,the NO adsorption performance of the MAC was reduced.Compared to the original activated carbon,the NO adsorption performance was still greatly improved.The metal oxide and surface functional groups introduced by the modification process improved the practical performance of the material to a certain extent.Secondly,the adsorption mechanism and the influence of preoxidation treatment:the samples were characterised by N2 adsorption at-196?,XRD,SEM,BET,ICP,FTIR,XPS and Ion chromatography analyses.The adsorption mechanism of NO by MAC and the effect of different pre-oxidation treatments on the properties of the material and its NO adsorption property were investigated.The MnxCeyOz loaded in the form of nano rod or nano foam structure on the surface and pores of MAC.The active lattice oxygen in MnxCeyOz was beneficial to the storage and transfer of oxygen,and Mn4+ was the most active reaction site of NO catalytic oxidation.There appeared to exist a strong synergistic effects between the MnOx and CeOy that was mediated by the surface oxygen-containing functional groups,leading to enhanced stable NOx adsorption toward the formation of nitrites and nitrates.The preoxidation treatment played an important role in creating mesoporous or macroporous structures and introducing surface chemical functional groups.It promoted the uniform distribution and loading of metal oxides on the surface and pores of the material,optimized the occurrence state of metal oxides,promoted the mobility of oxygen and electrons,improved the surface chemical activity of MAC and then improved the denitration performance of the material.Air treatment created the maximum total specific surface area and total pore volume of the material.KMnO4 treatment introduced the most Mn and O on surface,and the lattice oxygen in surface oxygen accounted for the most.The NO adsorption effect of the sample prepared by HNO3 preoxidation was the best,which due to the introduction of oxygen and nitrogen-containing functional groups such as O-H,C=O,C-O,?-?bonds,pyridine and pyrrole,etc.Finally,the process and mechanism of regeneration.The thermal regeneration and water washing regeneration treatments were carried out on the nitrogen-loaded Mn-Ce modified activated carbon.Combined with various characterization methods,the physical and chemical properties of the materials during the regeneration process and the regeneration mechanism were researched.In the thermal regeneration process of nitrogen-loaded activated carbon,the adsorption products were mainly resolved in the temperature range of 120-300? and the highest resolution peak was generated at 173?.The evolved gas was mainly NO,which was also accompanied by the generation of CO2 and CO due to the reduction of adsorbed product C-NO2 by C.With the release of NO,the Mn-Ce metal oxide on the MAC obtained lattice oxygen and the catalytic activity was restored.In the regeneration process of water washing,the adsorbate existed in the water washing liquid in the form of NO3-.Both regeneration methods restored the physical and chemical properties of the material,but the active oxygen and surface functional groups on the material had been partially irreversible. |
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