Study On CO-SO₂ Reaction And Synergistic Reduction Of Sulphur And Nitrate Based On Fe-Zr Catalyst

SO2 and NOx are common air pollutants,without treatment,it will not only bring serious environmental problems,but also endanger human health,so it is urgent to explore efficient methods of desulfurization and denitrification.At present,flue gas desulfurization and denitrification are generally handled separately,and the process is complicated.Compared with desulfurization and denitrification products such as gypsum and strong acid,catalytic reduction method for desulfurization and denitrification is popular because its reduction products are China’s scarce resource elemental sulfur and harmless gas N2.At the same time,CO generally coexists with SO2 and NOx in flue gas,and has a wide range of sources,so it is very promising to reduce SO2 and NOx with CO.At present,however,there is little research on the synergistic reduction of sulfur and nitrate at high SO2 concentration.Zirconia is the only metal oxide with both acidity,basicity,oxidation and reducibility.It is easy to generate holes,can have strong interaction with active components,and will lower the activation temperature;Fe-based metals catalyst have lower activation temperature and higher catalytic performance for CO reduction of SO2 and NO.Therefore,in this paper,the Fe-Zr catalyst was prepared by citric acid combustion method,which was used for CO catalytic reduction of SO2,and the synergistic catalytic reduction of SO2 and NO with high SO2/NO ratiowas explored.Its double-effect desulfurization and denitrification performance and mechanism were explored by means of activity experiments and XRD,XPS,SEM,in-situ DRIFTS and other characterization methods.In this paper,firstly,the preparation and evaluation optimization of catalyst are carried out.According to the activity evaluation experiment of the catalyst,when the molar ratio of Fe/(Fe+Zr)is 0.4 and the calcination temperature is 500℃,the prepared catalyst has the highest activity.Under the experimental conditions of temperature reaction at 400℃ CO/SO2 molar ratio of 3.5:1 and space velocity of 6000h-1,the SO2 conversion rate can reach 98%and the average sulfur yield can reach 82%within 2 hours.XRD characterization shows that the active component of the catalyst is FeS2,which will be transformed into Fe1-xS at high temperature.The S element in Fe1-xS is inactive,and the activity of the catalyst will be weakened.Compared with pure ZrOx and pure FeOx,Fe(y)has larger specific surface area,more developed pores,and more weak acid sites and strong acid sites.The acid sites can promote the reduction of SO2 by CO.Then,the experiment and mechanism of sulfur-nitrate synergistic reduction based on the optimized catalyst were carried out.Studies have shown that the addition of NO will reduce the conversion rate of SO2,and the higher of the NO concentration,the more obvious of the effect.But at the same time,the average denitration rate is over 95%,which shows that the catalyst has good denitration performance.Temperature has little influence on desulfurization and denitrification activity of catalyst.The mechanism study shows that both CO catalytic reduction of SO2 and sulfur-nitrate synergistic reduction are carried out according to the mixing mechanism of Redox-COS intermediates.At the initial stage of the reaction,the conditions for the formation of COS intermediate mechanism were not met,so Redox mechanism was followed.With the gradual vulcanization of Fe2O3 into FeS2,COS intermediate mechanism dominated,and the overall reaction was carried out according to Redox-COS intermediate mixing mechanism.Finally,the water resistance and oxidation resistance of the catalyst were tested,and the pretreatment solution and system design for flue gas containing complex components such as water and oxygen are put forward.The addition of water vapor will occupy the active sites,but will not inactivate the active components.O2 will rapidly oxidize the active component FeS2 to Fe2O3,and then lose its catalytic activity.To solve the problem that O2 easily lead to catalyst deactivation,the O2 in the flue gas was removed in advance by the reaction of the fungus bran semi-coke with the flue gas,and the flue gas after deoxidization and conditioning passed through the catalyst.From the activity test results,it can be seen that the SO2 conversion rate can reach 97%.In order to solve the problems of O2,H2O and other catalyst failures,reduce catalytic efficiency,and CO sources of reducing agents in flue gas,combined with the results of catalyst resistance experiment and semi-coke deoxidization,the system design of sulfur-containing flue gas quenching and co-disposing of carbon-containing solid waste is carried out,which not only solves the above problems but also realizes the collaborative utilization of matter-energy,which not only disposes of carbon-containing solid waste,but also realizes the recycling of waste heat.