Study On Low Temperature SCR Denitrification Performance Of Ce Doped VPO Catalyst Supported On TiO₂

NO_x is one of the main pollutants causing photochemical smog,haze and acid rain in China.At present,the main method used for the treatment of NO_x is the selective catalytic reduction（SCR）.The coal-fired flue gas is a major source of NO_x and generally treated by commercial V₂O₅-WO₃/TiO₂ catalysts.Because of the limit of active temperature window（300⁴00℃）,the coal-fired flue gas denitration catalyst,which is directly disposed between the economizer and the air preheater,is easily deactivated due to clogging and poisoning.If the coal-fired flue gas denitration reactor is installed after the dust removal device,the service life of the catalyst will be greatly prolonged and the denitrification operation cost will be reduced,but the active temperature window of the catalyst needs to be reduced.In addition,the industrial flue gas is another an important NO_x pollution source.The temperature of industrial flue gas is often lower than that of coal-fired gas,so the V₂O₅-WO₃/TiO₂ catalyst is not suitable for NO_x treatment of industrial flue gas.Therefore,the research of low temperature denitration catalyst has important theoretical significance and engineering application value on the treatment of NO_x in industrial flue gas and prolonging the service life of coal-fired flue gas denitrification catalyst.Titanium dioxide supported Ce modified vanadium phosphate catalyst was prepared and its denitrification performance and structure characteristics were studied,which amied the problem that the activity of low temperature SCR denitration catalyst was susceptible to SO₂ and H2 O in flue gas.（1）The TiO₂ supported the transition metal elements M（Ce,Mo,Cr,Cu,Mn）modified VPO catalysts were prepared by impregnation method,and the denitrification activity was investigated.The research results showed that VPO-Ce/TiO₂ catalyst had the best low temperature denitrification activity.Then on this basis,the VPO-Ce/TiO₂ catalysts were prepared by changing the P/V（molar ratio）,Ce/V（molar ratio）,calcination temperature and VPO-Ce loading.The effects of these factors on the denitrification activity of the catalyst were investigated by the activity test.The experimental results showed that when the P/V（molar ratio）is 1:3,Ce/V（molar ratio）is 1:4,calcination temperature is 400 ℃and VPO-Ce loading is10%,the 10V（3）PO-Ce/TiO₂ catalyst show the best denitrification activity,and the NO_x conversion rate is 96.1% at 250℃.In addition,the physic-chemical properties of10V（3）PO-Ce/TiO₂ catalyst were characterized by XRD,BET,SEM,H2-TPR,XPS,NH₃-IR.The characterization analysis results showed that the addition of Ce reduced the catalyst diameter and agglomeration,enhanced the dispersion of the active components,promoted the formation of redox couple（Ce3+/Ce4+）,increased the specific surface area of the catalyst and the adsorption oxygen content,thereby enhancing the efficiency of the NO_x treatment of the catalyst.（2）The effects of process parameters（reaction temperature,reaction space velocity,ammonia-nitrogen ratio,oxygen content and inlet NO concentration）on the denitrification performance of 10V（3）PO-Ce/TiO₂ were studied.The experimental results showed that the NO_x conversion rate increased with the increase of reaction temperature and the maximum conversion rate was 98.7% at 300℃.The conversion efficiency of NO_x was basically the same when the NH₃/NO ratio was in the range of0.7¹.2.The removal efficiency of NO_x could be enhanced by increasing the oxygen content.However,when the O₂ content was more than 6vol.%,the NO_x conversion rate was hardly affected by the increase of oxygen content.The NO_x conversion rate was maintained in a relatively stable state when the NO concentration varied from200⁶00ppm.Moreover,the effect of SO₂ and H2 O on the catalytic reduction of NO_x in10V（3）PO-Ce/TiO₂ catalyst were investigated.The research results showed that when the SO₂ concentration was in the range of 200⁸00ppm,the conversion rate of NO_x was kept above 95%,and the catalyst exhibited better sulfur resistance.When200ppmSO₂ and 4vol.%H2O were simultaneously added,the conversion rate of NO_x was about 90% at 250℃,which was similar to that of SO₂ alone,reflecting the better anti-SO₂,H2 O poisoning capacity.The FT-IR test result showed that the characteristic peaks of the sulfate species were not observed on the catalyst surface.（3）The reaction kinetics of 10V（3）PO-Ce/TiO₂ catalyst was studied.The effects of inlet NO concentration,NH₃ concentration,oxygen content and reaction temperature were investigated.The results showed that the reaction order of inlet NO concentration,NH₃ concentration and O₂ concent were 0.812,0.568 and 0.091 respectively.The reaction activation energy of the catalyst was 30.67KJ/mol.