Study On Preparation,Process And Performance Of Non-toxic De-NO_x Catalyst

Nitrogen oxides（NO_x）are a series of major atmosphere pollutants and harmful to ecological environment and human health.Selective catalytic reduction（SCR）is one of the most effective methods to remove nitrogen oxides.NH₃-SCR has been applied in denitrification field for several years.De-NO_x catalyst is a main component of NH₃-SCR.Because V₂O₅ used in V-W-Ti catalyst is highly toxic,V₂O₅ would lead to hazards and secondary pollution.Therefore,the study of non-toxic SCR catalyst is an important part in denitrification field.In this paper,a series of Nb-W-Ti non-toxic catalysts were prepared by integral extrusion process,including the catalysts modified by rare earth elements Ce,Y,Pr,Nd and transition element Cr.Activities of the obtained catalysts were measured by simulated de-NO_x apparatus,and properties were characterized by BET,XRD,SEM,XPS and H₂-TPR.The results are as follows:（1）In the experiment,optimum reaction temperature is 350℃.Denitrification efficiencies of Nb-W-Ti non-toxic catalysts at 330℃-390℃are more than 90%.（2）The optimum loadings of all active components are different.Optimum loading of Nb is 2.8%and denitrification efficiency is 95%.Lowering the loading of Nb to 1.1%,optimum doping amounts of Ce,Y,Pr and Nd are 1.5%,1.0%,1.5%and 2.0%,and their best denitrification efficiencies are more than 95%,which are higher than the best denitrification efficiency of 2.8%Nb.Optimum doping amount of Cr on 1.1%Nb-W-Ti catalyst is 1.0%,and denitrification efficiency is up to 97%.（3）Catalysts are sorted by abilities to sulfur poisoning resistance in descending order:1.0%Ce-1.1%Nb,1.0%Cr-1.1%Nb,2.8%Nb,1.0%Y-1.1%Nb,1.5%Pr-1.1%Nb,2.0%Nd-1.1%Nb.Ce oxides may interact with Nb oxides,inhibiting the production and deposition of ammonium sulfate or metal sulfate.（4）SO₂ poisoning mechanism of Nb-W-Ti non-toxic catalysts:SO₂ reacts with the reductant NH₃ and the obtained substances ammonium sulfates deposit on the surface of catalysts,cover the active site,and reduce the amount of active center.Ammonium sulfate would gradually decompose if the amount of SO₂ is reduced.Micro-pores and active sites would be restored and denitrification activity could be restored.SO₂ poisoning in this case is reversible.SO₂ can also react with the active components to form inactive metal sulfate.In this case,the content of active component decreased,and denitration efficiency decreased.The catalysts are difficult to regenerate and SO₂ poisoning is irreversible.Nd oxides can react with SO₂.The products neodymium sulfate is inactive and micro-pores in the catalyst could be plugged,which is a typical irreversible poisoning.