Preparation Of Blast Furnace Slag-based Supported Catalyst And Study On The CO-SO₂ Catalytic Reduction Performance

Coal is used as the main energy source in China,and the SO2 produced by the power and metallurgical industries seriously endangers the residents' health and ecological environment.Therefore,SO2 emissions are strictly restricted in industrial production.At present,the limestone-gypsum method is the most widely used for flue gas desulfurization,and its product is desulfurized gypsum with low utilization value.In contrast,suifur is the most ideal desulfurization product because China has a large demand for sulfur and it is easy to store and transport.At the same time,CO,as a reducing gas coexisting with SO2 in the flue gas,has strong reaction operability,which can eliminate high-purity sulfur while eliminating CO and SO2 pollution.Therefore,CO catalytic reduction of SO2 to produce sulfur is a promising desulfurization method.The reduction of flue gas desulfurization requires the assistance of catalysts,and thecurrently studied catalysts generally suffer from high costs and incomplete mechanisms.Low-titanium blast furnace slag is a by-product in the steelmaking industry and is generally used to produce cement or rough utilization as the building materials additive.It has excellent stability and strength,and its main components are CaO,MgO,Al2O3,and SiO2,so it can be regarded as an inexpensive composite support material.In this paper,the ground blast furnace water slag fine powder is used as a carrier,and inexpensive transition metals are used as active components.The metal oxide supported catalyst is prepared by the impregnation method.A systematic study of its reduction and desulfurization performance was conducted to explore the optimal reaction conditions and preparation conditions of the catalyst.In addition,XRD,XRF,XPS,and in-situ DRIFTs were used to characterize the catalyst before and after the reaction to investigate the phase change and gas adsorption of the catalyst surface during the reaction.Combined with the catalyst life test,the poisoning mechanism and complete reaction path of the catalyst were revealed.First,blast furnace slag was selected as the catalyst support and Fe was used as the supported active component.An environmentally friendly and efficient desulfurization catalyst was successfully prepared.The effects of temperature,loading capacity and space velocity on desulfurization performance were studied.Through comparative analysis,the optimal reaction conditions are 15%loading,500? reaction temperature,and 6000h-1 space velocity.At this time,the SO2 conversion rate is stable above 90%,and the average sulfur yield is also can reach more than 80%within 2h of the reaction.The surface of the blast furnace slag catalyst is rich in strong acidic sites,which can produce a strong adsorption of acid gas SO2.On the one hand,this strong adsorption improves the reaction efficiency,so that the catalyst does not need to be sulfided in advance to reach nearly 100%SO2 conversion in the early stage of the reaction;on the other hand,it can sulfide metal oxides to produce catalytically active phase FeSx to complete the sulfur resource recycling.Characterization of in-situ DRIFTs shows that the adsorption of SO2 on the catalyst is irreversible,and an unstable state of sulfate will be generated.The gas phases CO will not be adsorbed on the catalyst surface,but directly react with the adsorbed SO2.At the same time,the reaction of hydroxyl groups on the catalyst surface with SO2 will generate H2O,which provides a reasonable explanation for the occurrence of H2S in the tail gas.Based on this research,the catalyst carrier and supported metal components were optimized to reduce the reaction temperature and improve the desulfurization performance of the catalyst.With the increase of the content of Al2O3 and TiO2,the specific surface area of the blast furnace slag will increase,which will be more conducive to metal loading and gas circulation.The finely ground slag powder will further optimize the catalytic performance due to the enhancement of specific surface area and activity.The focus is on the introduction of transition metal Co.Adding 4%Co3O4 on the basis of 15%Fe2O3 will reduce the reaction temperature to 400?.At this time,the SO2 conversion rate is maintained above 90%,and the average sulfur yield exceeds 80%.The addition of Co3O4 enhances the intensity of the reduction peak of the catalyst,making the temperature range corresponding to the reduction peak position wider and the reduction reaction easier to occur.Adding an appropriate amount of Co will also increase the intermediate acidic sites while maintaining strong adsorption active sites on the catalyst surface,making the catalyst's adsorption temperature range wider and more conducive to SO2 adsorption.Similar to single metal catalysts,Fe3+and Co3+will be reduced to Fe2+and Co2+ under the CO atmosphere,and then the active phases FeSx and CoSx of the metal sulfide will be formed.Finally,a 15%Fe2O3-slag catalyst was subjected to a life test.After about 4 hours of reaction,a stable sulfate appeared on the catalyst surface occupying a large number of active oxygen vacancies,and metal sulfides and COS could not be successfully formed,resulting in irreversible sulfur poisoning.The SO2 conversion continued to decrease,and the catalyst was completely deactivated after 12h.Flue gas reduction desulfurization is subject to the sulfurization of metal oxides,the generation of COS,and the recovery of elemental sulfur.At the beginning of the reaction,because metal sulfides have not yet formed,the Redox mechanism occupies a dominant position to sulfide metal oxides,and the SO2 conversion rate remains high under strong adsorption.With the progress of the reaction,a large amount of metal sulfides and COS are formed,and COS reduces SO2 to complete sulfur recovery.At this time,the reaction follows both the Redox reaction path and the COS intermediate product path,the latter occupying a dominant position.The water vapor generated by the reaction will produce H2S through a complex reaction process,but it does not damage the surface structure of the catalyst and and affect the catalytic performance as a whole,which indicates that the catalyst has certain water resistance.