Study On NO_x And SO₂ Removal Process By CO Based On Carbon-based Catalyst And Adsorption Reduction Decoupling

CO is cheap and easily available,and its deNOx products are environmentally friendly.It has gradually been used as a reducing agent to replace NH3 for catalytic NOx removal.However,the selectivity of CO catalytic deNOx is poor,which is easily inhibited by oxygen in the flue gas.H2O and SO2 in the flue gas will also poison and inactivate the catalyst.Therefore,in order to avoid the inhibition of O2 and SO2 in flue gas on deNOx process by CO,the NOx and SO2 removal process based on carbon-based catalyst and adsorption-reduction decoupling was proposed.This removal process realizes that the catalyst adsorbs NOx under high oxygen and no SO2 conditions and reduces NOx under low oxygen and no SO2 conditions.In this paper,semi coke was used as the raw material of catalyst.FeCo/ASC catalyst with binary active components was prepared experimentally,and its adsorption-reduction dynamic NOx removal performance under different reaction conditions was explored.In order to further improve the deNOx efficiency of the catalyst in the rotary reactor,based on the above research,the FeCo/ASC catalyst was modified by nitrogen doping.The deNOx performance of the Ndoped catalysts were tested by experiments,and the surface key species promoting NOx removal were determined.The influence mechanism of nitrogen doping process on catalyst deNOx was clarified.Based on the catalyst adsorption-reduction dynamic deNOx process,the SO2 removal process in the rotary reactor was preliminarily explored.Semi coke was used as raw material of adsorbent,SO2 adsorbent with excellent adsorption and desorption characteristics was prepared.And the reaction conditions which can improve the SO2 removal efficiency were explored.The mechanism of sorbent adsorption and desorption of SO2 in the rotary reactor was clarified by characterization.Through quantum chemical theoretical calculation,the optimal adsorption configuration and energy barrier changes of NO and CO on the catalyst surface were explored,and the main path of NO reduction by CO on the catalyst surface was explored.In addition,the trapezoidal structure of seven six membered carbon rings was established to explore the adsorption and evolution of SO2 on the surface of activated semi coke,so as to provide theoretical support for practical application.The results showed that in the adsorption stage,the oxygen in the flue gas promoted the oxidation and adsorption process of NO,and different reaction conditions had different effects on the deNOx process of the rotary reactor.The reduction time of the rotary reactor increased from 30s to 60s,and the NOx adsorption efficiency and reduction efficiency increased from 49.2%and 8.9%to 72.9%and 15.3%,respectively.However,too long reduction time will inhibit the NOX adsorption process and reduce the NOx removal efficiency.The increase of reactor volume space velocity(GHSV)would significantly reduce the NOx adsorption efficiency in the adsorption stage.In the reduction stage,the influence of GHSV on the reactor was multifaceted.The gas flow rate of reducing gas affected the physical desorption process of NOx and the process of NO+CO at the same time.These two processes jointly promoted the removal of NOx.When GHSV was 12000h-1,the adsorption efficiency and reduction efficiency of NOx could reach 84.7%and 21.4%,respectively.The characterization study showed that the nitrogen oxide species on the catalyst surface were mainly free nitrate ions.Higher oxygen concentration could make more NOx stored on the catalyst surface in the form of nitrate ions,which was helpful to improve the adsorption efficiency of NOx.By exploring the effects of CO2,H2O and SO2 on the deNOx process of the rotary reactor,it was found that these three gases in the flue gas will inhibit the adsorption and reduction process of NOx,but heating up can greatly alleviate the effects of CO2 and H2O on the deNOx of the reactor.The nitrogen doping process can improve the specific surface area,metal relative content and surface nitrogen content of the catalyst,especially the contents of pyridine nitrogen(N-6)and pyrrolic nitrogen(N-5).On the catalyst surface,nitrogen doping can promote the conversion of Fe2+and Co2+ions to high priced Fe3+and Co3+ions,which is conducive to the adsorption and reduction of NOx.The deNOx activity test of N-doped catalyst found that the NOx adsorption capacity and catalytic activity of N-doped catalyst were improved.At 300℃,the NOx conversion rate can reach 99.1%.At the same time,the dynamic deNOx efficiency of N-doped catalyst in rotary reactor has also been significantly improved,among which Fe-Co/NASC-3 catalyst has the best NOx removal ability.Fe-Co/N-ASC-3 catalyst has the most developed microporous structure,high content of nitrogen species and rich active centers of metal oxides.At the same time,Fe-Co/N-ASC-3 catalyst has efficient adsorption and reduction of NOx at high temperature.In addition,two deNOx paths on the surface of N-doped catalyst in the process of dynamic NOx adsorption and reduction are summarized.The acid activated semi coke adsorbent(ASC-1)has better SO2 adsorption capacity,and the adsorption capacity can reach 25.59 mg/g.And the SO2 removal capacity of ASC-1 adsorbent is also better in the dynamic SO2 adsorption-desorption process in rotary reactor.Prolonging desorption time and increasing the desorption temperature can significantly improve the SO2 removal efficiency.However,excessively prolonging the desorption time has less and less impact on improving the SO2 adsorption efficiency.Therefore,for the rotary reactor,increasing the SO2 desorption temperature is an important way to improve the SO2 removal efficiency.When the desorption temperature was increased from 100℃ to 300℃,the SO2 adsorption efficiency could be increased from 52.5%to 80.7%.Under the purging of desorption gas,SO2 species on the adsorbent surface have two desorption paths,one of which is the weak adsorption of SO2 and some SO3 species directly desorb from the ASC adsorbent surface,which is also the main desorption path of SO2 species.The other way is that sulfate and some sulfite first combine with CO in the desorption gas,and then desorb from the adsorbent surface in the form of SO2 at a temperature lower than 300℃.At this temperature,no elemental sulfur is generated,while the combined CO is released in the form of CO2.When the reaction temperature is higher than 200℃,the second desorption path will be activated.DFT calculation shows that CoFe2O4(311)crystal surface is a suitable crystal surface for NO adsorption and CO reduction,and infers the most likely site for NO adsorption,that is,the N atom of NO tends to be adsorbed at the Co site,the maximum adsorption energy is-1.64eV,and NO molecule can be activated.The C-terminal adsorption energy of CO on Fe is the largest,which is-1.57eV,and the CO molecule is also activated,which is conducive to the next reaction with nitrate species.After NO+O2 is adsorbed on the catalyst surface,the O-O bond of O2 is stretched and O2 molecules are activated in an active state,which can form nitrate(NO3-),bidentate nitrate and bridged nitrate on the catalyst surface and release a lot of heat.However,the energy barrier of the reaction of these three nitrates with adsorbed CO is high.Among them,the energy barrier of CO combined with*ONO to produce*N2O2 and release CO2 is 0.84eV,which is difficult to carry out the reaction at low temperature.And the energy barrier for the subsequent generation of N2 is 0.75ev.Therefore,only at higher temperatures can the nitrate species be completely reduced to N2.At lower temperatures,due to the inability to overcome the energy barrier,the intermediate product*N2O2 will release N2O after reacting with CO.In addition,the trapezoidal structure of seven six membered carbon rings was established to explore the adsorption and evolution of SO2 on the surface of activated semi coke.The unsaturated carbon atoms at the edge of the activated semi coke are the main adsorption active site.SO2 and O2 molecules are easy to adsorb on the unsaturated carbon,and O2 molecules are easier to adsorb on the surface of the activated semi coke than SO2.The oxygen in flue gas adsorbed on the active semi coke surface will form OSO-or-SO3-structure,and the adsorption process will form carbonyl structure on the active semi coke surface,which has little impact on the subsequent evolution of SO2 species.When activated semi coke is regenerated in CO atmosphere,the orbitals of SO2 species will hybridize with those of CO molecules,and CO tends to adsorb on the S side to form a five membered ring.After adsorbing CO molecules,the energy required for SO2 desorption on the surface of activated semi coke is lower than that of SO2 direct desorption,that is,CO can promote the desorption process of SO2 on the surface of activated semi coke.Through the above research,fast and efficient adsorption-reduction decoupling deNOx catalyst and adsorption-desorption decoupling deSO2 adsorbent were developed.And this research establishes the decoupling removal path of SO2 and NOx,realizes the rapid and deep regeneration promoted by CO,and establishes the surface SO2 and NOx desorption and reaction process mechanism participated by CO,which provides sufficient theoretical support for the application of adsorption desorption cycle desulfurization and denitrification technology.