Studies On Low-temperature NH₃-SCR Performance Of Ni-Mn-O_x Catalysts

At present,industrial flue gas and automobile exhaust emissions of nitrogen oxides?NO_x?has become the main pollutants in the atmosphere and it has a great harm on the environment and the human body.Low temperature selective catalytic reduction?NH₃-SCR?has become the most widely used and most promising method for NO_x removal technology due to its high denitrification activity,low temperature window and non-pollution in the severe pollution situation.The development of highly efficient low temperature SCR catalysts has become the focus of research in the field of flue gas denitrification.Mn-based mixed metal oxide catalysts have good catalyst activity at low temperature,and the SCR performance of mixed oxides of Mn and various transition metals has been reported and showed good SCR activity.It has been reported that the addition of Ni improves the SCR activity of pure MnO_x.However,the catalysts reported previously are mostly prepared by coprecipitation method and have small specific surface area and pore volume.Therefore,the preparation of mesoporous Ni-Mn catalysts with high SCR activity,high specific surface area and pore volume has become the research content of this paper.The catalysts were synthesized via hard template by using KIT-6 or SBA-15 as the hard templates,Ni?NO₃?₂·6H₂O and Mn?AC?₂·4H₂O as the precursors and ethanol as the dispersing agent.A series of Ni-Mn-O_x oxides with different Ni/Mn molar ratios were prepared and their physical properties and structure were characterized by BET,XRD,TEM,SEM and XPS to investigate the effects of the structure on the NH₃-SCR performance.From the characterization results,large specific surface area,the presence of amorphous phase and the presence of Mn⁴⁺and chemisorbed oxygen which are favorable for catalytic reduction,are likely to be beneficial to the low temperature NH₃-SCR activity of the catalyst.In this paper,the NH₃-SCR performances of Ni-Mn-O_x catalysts with KIT-6 and SBA-15 as templates were studied.The results showed that the SCR activity of Ni-Mn-O_x catalyst with KIT-6 as template was higher than that of SBA-15.In these two catalysts,when the Ni/Mn molar ratio is 1:3,the SCR activity is higher than other catalysts.The effect of GHSV on the SCR activity of Ni?1:3?-MnO_x catalyst was also investigated.The results showed that the Ni?1:3?-MnO_x catalyst with KIT-6 as the template still had high NO conversion at higher gas flow rates,whereas the NO conversion of Ni?1:3?-MnO_x catalyst with SBA-15 as the template is much lower at high GHSVs.The effect of calcination temperature on the SCR performance of Ni?1:3?-MnO_x catalyst was also investigated.The results show that the calcination temperature could lead to the sintering of the catalyst and decrease the specific surface area of the catalyst.Consequently,the active sites on the catalyst surface were decreased.Moreover,the crystallinity of the catalyst increased and the amorphous phase disappeared,the NH₃-SCR activity of the catalyst was decreased.At the same time,the two catalysts have good stability and good H₂O resistance,the addition of nickel can improve the H₂O resistance of pure MnO_x catalyst.