The Synthesis Of Transition Metal Modified SAPO-34 And Its NH₃ Selective Catalytic Reduction Of NO_x Performance

With the rapid development of the national economy,the number of vehicles has been increased year by year.Although they bring convenience to human beings,the emission of its tail gas NOx has also brought tremendous environmental problems to people.Especially,the emission of NOx from diesel vehicles is the main pollutant to the environment.Selective catalytic reduction with NH₃ is considered to be the most effective technologies to remove NOx.At present,the commercial catalysts（V2O5-WO3（MoO3）/TiO2）for large electric field has the disadvantages of high NOx conversion temperature,narrow operation temperature window and V species with biological toxicity,the catalyst is not applicatable to the elimination of NOx.Therefore,it is a hot spot of research to design an effective NH₃-SCR catalyst.Recently,metal modified molecular sieves with small pore CHA structures have received extensive attention due to their high NOx conversion,N₂ selectivity and excellent resistance of H₂O and SO₂ in the NH₃-SCR reaction.MnNi-SAPO-34,Cu/SAPO-34 and hierarchical pore Cu/SAPO-34（Cu/SAPO-34-H）are prepared by different method,in the same time,the catalytic properties of MnNi-SAPO-34,Cu/SAPO-34 and Cu/SAPO-34-H are studiedin this paper.XRD,XRF,SEM,TEM-EDX,UV-Vis-DRS,NH₃-TPD,XPS,NMR and in situ DRIFTS analyses were revealed to study the impact of different metal modification and different pore structure of SAPO-34 on NH₃-SCR of NOx.MnNi-SAPO-34 catalyst was synthesized by one step hydrothermal method,and the catalytic activity shows that the NOx conversion can achieve 95%in the range of320-470 ^oC at the GHSV of 40,000 h^-1.Then,the MnNi-SAPO-34 catalyst was aged by600 ^oC,it is found that the activity of hydrothermal aging catalysts has a little impact.It is due to the synergistic effect of Mn and Ni(Ni³⁺+Mn³⁺→Ni²⁺+Mn⁴⁺).The hierarchical pore SAPO-34 was synthesized by hard template method,and subsequently synthesized Cu/SAPO-34-H series catalysts by impregnation and ion exchange method.The activity test showed that theCu/SAPO-34-HI catalyst prepared by impregnation and ion exchange method all exhibited excellent SCR de-NOx activity and N₂ selectivity,and the activity of Cu/SAPO-34-HE is better than traditional Cu/SAPO-34 catalyst.The6.3wt.%Cu/SAPO-34-HI catalyst by impregnation method shows the NOx（>90%）conversion from 180 ^oC to 400 ^oC at the GHSV of 40000 h^-1.However,2.7wt.%Cu/SAPO-34-HE catalyst shows NOx（100%）in the range of 150-450 ^oC.And compared to the Cu-SAPO-34-H synthesized by the impregnation method,Cu-SAPO-34-H synthesized by the ion exchange method shows the excellent hydrothermal stability and resistance to H2O and SO2.The results shows that the hierarchical structure of SAPO-34 can well dispersed the Cu species,in the same time,the more isolated Cu species were generated.It is beneficial to the adsorption and activation of the reactant gas molecules,and also increases the diffusion rate of the reaction gas,thus improving the de-NOx activity of NH₃-SCR.