Study On The Preparation Of Supported Co Modifying VPO Catalyst And Its Catalytic Performance For NO Oxidation

Nitrogen oxides?NO_x?emitted by coal combustion?NO>95%?is one of the major air pollutants in China.Selective catalytic reduction?SCR?technology is widely used at home and abroad to remove?NO_x?.However,NO_x is also a resource.If the water-insoluble NO is catalyzed and oxidized to the more soluble NO₂,the use of ammonia with higher chemical activity to remove NO₂ and SO₂ together enables the simultaneous recovery of sulfur and nitrogen resources.It will be a denitrification technology with great application prospects.For oxidation of NO to NO₂,the catalytic oxidation method?SCO?is currently widely applied.This method does not need to add oxidants and has no secondary pollution.Catalyst is the key to achieve denitration technology.However,the acid gas SO₂ present in the flue gas is easily adsorbed on the surface of the catalyst to cause catalyst poisoning.According to the enhancement of surface acidity of the catalyst,the adsorption of SO₂ and the sulfation of active components are inhibited,and the catalyst's anti-poisoning capacity is improved.In this paper,vanadium is used as an active precursor,and then phosphoric acid is added to prepare vanadium phosphorus oxide?VPO?.The VPO is then loaded on the support TiO₂to increase active site exposure.The doping of the transition metal promoter Co is to further regulate the Br?nsted,Lewis acid sites on the surface of the vanadium phosphorus oxide,and to enhance the activity and anti-poisoning ability of the catalyst.In this paper,the characteristics of VPO-Co/TiO₂ catalyst,the mechanism of NO oxidation and its anti-toxicity were studied by use characterizations.The activity test was used to screen out the optimal catalyst preparation conditions.The results showed that NO conversion could reach 71%when P/V?molar ratio?was0.33,Co/V was 0.07,VPO loading of the active component was 10%,the catalyst was calcined at 450?,and the reaction temperature was 350?.The characteristics of the catalyst 10VP?0.33?O-Co?0.07?/TiO₂ were studied by using characterization methods such as BET,H₂-TPR,SEM,XPS,and FTIR.The results show that the doped cobalt catalyst has the advantages of good crystallinity,large specific surface area,high mesopore ratio and strong redox property.The XPS test result shows that the surface of the catalyst contains more chemical adsorbed oxygen,which can promote the oxidation of NO.It is also shown that Co₃O₄ plays a major role in the catalyst.SEM result has a complete"rose petal"structure for the active component of the catalyst,which is beneficial to the improvement of the activity of the catalyst.FTIR shows that the active phase of the catalyst for the catalytic oxidation of NO is vanadyl pyrophosphate?VO?₂P₂O₇.According to the characterization and the structure of the catalyst,the mechanism of NO oxidation catalyzed by the catalyst is that V⁴⁺=O as the active site for NO adsorption generates synergy with V⁵⁺=O.The doped cobalt catalyst VPO-Co/TiO₂ and the undoped cobalt catalyst VPO/TiO₂were carried out the SO₂ and H₂O resistance activity tests.The results showed that when600 ppm SO₂ and 4vol.%H₂O were used in the flue gas,the NO oxidation rate of the catalyst VPO-Co/TiO₂ was up to 67%,while the NO oxidation rate of the catalyst VPO/TiO₂ was only 50%.The FTIR characterization of the cobalt-doped catalyst after the SO₂ and H₂O resistance test showed that there was no SO₄^2-formation on the catalyst surface.Further NH₃-IR characterization showed that doping of cobalt promoted the formation of more Br?nsted acid sites in the catalyst,increased the surface acidity of the catalyst and thus enhanced the resistance to poisoning.In addition,the effect of process conditions on the catalytic oxidation of NO by the catalyst was investigated.The results showed that the NO oxidation rate decreased with the increase of the reaction space velocity.When the space velocity is 5000h^-1,the NO oxidation rate reaches 92%,and when the space velocity is 15000 h^-1,the NO oxidation rate reaches 71%.The NO oxidation rate decreases as the NO import concentration increases.The NO oxidation rate increases gradually with the increase of oxygen content,and the change is not significant when the oxygen content is large.Kinetic studies showed that the reaction of NO oxidation with 10VP?0.33?O-Co?0.07?/TiO₂ catalyst was0.80 for NO and 1.52 for O₂.At the same time,the internal and external diffusion of NO and O₂ on the catalyst has a negligible effect on the catalytic oxidation of NO.