Study On The Influence Mechanism Of Sulfur And Water On Pt-based Catalysts In Iron And Steel Sintering Flue Gas CO Oxidation

With the completion of the transformation and upgrading of ultra-low emission of thermal power industry,the emission of air pollutants from iron and steel industry has become the largest emission source of China's industrial sector.In April 2019,five ministries and commissions led by the ministry of ecology and environment jointly issued the opinions on promoting the implementation of ultra-low emission in the iron and steel industry,which promotes the upgrading of ultra-low emission in the non-electric industry.In the process of iron and steel production,sintering process accounts for the largest proportion of air pollutant emission.At present,among many purification technologies of iron and steel sintering flue gas,medium and low temperature SCR denitrification combined with semi-dry absorption technology has gradually become the mainstream technology because of its high purification efficiency of SO₂ and NO_x,good system stability,collaborative removal of dioxins and other advantages.However,there are some shortcomings that a large amount of blast furnace gas is needed to be consumed for heat supplement,while the high concentration of CO(about 1%)in the sintering flue gas is not effectively controlled.In the CO purification technology,catalytic oxidation is the most efficient,energy-saving and no secondary pollution purification method.In addition,CO oxidation exothermic can supply heat for SCR denitrification at medium and low temperature.Even after desulfurization of sintering flue gas,there is still 10%H₂O and 10-35 mg/m³ SO₂,so it is necessary to overcome the water and sulfur resistance of the catalyst.In the atmosphere containing SO₂,the noble metal Pt as the active center is not easy to be sulfated,which showed a better ability to resist SO₂ poisoning.In the atmosphere containing H₂O,on the Pt-based catalyst,H₂O can change the reaction path of CO,thus promoting its oxidative removal.Therefore,Pt was selected as the active component to investigate the effects of six typical supports on the CO oxidation activity,so as to optimize the supports.Furthermore,the effects of preparation conditions and Pt loading on the catalytic performance were studied.The effects of H₂O,SO₂,H₂O and SO₂ coexisting atmosphere on the catalytic activity of CO oxidation and its mechanism were systematically studied.On this basis,the acid promoter WO₃ was used to improve the anti SO₂ ability of the catalyst,broaden the CO oxidation temperature window of the catalyst,and explain the reason for the improvement of the anti SO₂ ability of the catalyst through the corresponding characterization.The main contents and conclusions are as follows:(1)The results show that the Pt catalyst supported on anatase TiO₂-A has the best CO oxidation activity,and the optimal calcination temperature and time of0.1Pt/TiO₂-A catalyst are 500°C and 2 h,respectively.Considering the cost of catalyst in engineering application,the optimal Pt load is 0.1%.On the 0.1Pt/TiO₂-A catalyst,H₂O greatly promoted the CO oxidation,and 10%H₂O had the greatest effect,while SO₂ inhibited the catalytic oxidation of CO,which was positively correlated with the concentration.The 24 h stability evaluation in the coexistence atmosphere of10%H₂O and 50 ppm SO₂ showed that the promotion effect of H₂O was significantly greater than the inhibition effect of SO₂,and the CO oxidation activity was maintained at about 85%.(2)Pt species were uniformly dispersed on the surface of the TiO₂-A carrier in the form of nanoparticles.The amount of sulfate species deposited on the0.1Pt/TiO₂-A catalyst treated with H₂O and SO₂ atmospheres for 6,12,and 24 h was consistent,indicating that no significant sulfur deposition occurred on the surface of the Pt-based catalyst.The introduction of H₂O into the reaction atmosphere would cause the oxidation of Pt species to be reduced to Pt⁰,thereby weakening the strength of CO adsorption.H₂O continuously dissociated into*OH on the catalyst surface,providing oxygen species for CO oxidation.The H₂¹⁸O isotope labeling experiment proved that H₂O changed the CO oxidation pathway,and 88.9%of the O atoms in the product CO₂were derived from H₂O.Based on these results,the reaction mechanism of H₂O promoting CO oxidation at the interface of Pt-TiO₂ was proposed.(3)The optimal doping amount of acidic additives WO₃ was 5%,and accordingly,the complete conversion temperature of CO decreases by 20°C.WO₃ existed in an amorphous state and is evenly dispersed on the surface of the catalyst.On the0.1Pt-5WO₃/TiO₂-A catalyst,H₂O promoted O₂ activation to react with CO to form carbonate species.The decomposition of carbonate species to form CO₂ is the main pathway of CO oxidation.In addition,H₂O also participated in the CO oxidation reaction,contributing 44.2%of the oxygen atoms in the product CO₂.The intermediate product of H₂O involved in CO oxidation is HCOO*species.In the temperature range of 198?290°C,WO₃ species inhibited the adsorption of SO₂ on the catalyst surface,so that the 0.1Pt-5WO₃/TiO₂-A catalyst gave better CO oxidation activity.