Experimental Study And Simulation Analysis Of The Effect Of Ce Doping On The Water And Sulfur Resistance Of Mn-based Denitration Catalysts

Nitrogen oxides are one kind of air pollutants that destroy the atmosphere and cause great harm to human health and the ecological environment.Selective catalytic reduction?SCR?technology is currently the most widely used technology for removing NOx from combustion flue gas,which is highly efficient,stable operation,and is relatively mature.However,low-temperature catalysts are subjected to poisoning by water vapor and sulfur vapor in the flue gas,which reduces the efficiency and even causes the catalyst to be deactivated,and it is of practical significance to improve the water and sulfur resistance of the low-temperature catalysts.Therefore,aiming to solve the above problems,this article took Mn-Ce-based catalyst as the research object,and explored the effect of water vapor and sulfur vapor in flue gas on the denitration performance of Mn-Ce-based catalyst through a combination of experimental research and theoretical simulation,the main research contents were as follows:Firstly,a series of Mn-Fe-Ce/ZSM-5,Mn-Fe/?-Al2O3,Mn-Fe/ZSM-5,Mn-Fe-Ce/?-Al2O3 and Mn-Fe-Ce/Silicalite catalysts were prepared by impregnation,denitration experiments and resistance experiments were carried out in turn.The experimental conditions are that the mass concentration of NOx in the simulated flue gas was 500mg/m³,the volume concentration of NH₃ was 3%,the carrier gas was nitrogen and oxygen,the oxygen content was 9%,and the space velocity was 7500h-1.When Ce loading was 0.075mmol/g,the catalyst had the highest denitrification activity.Repeatable experiments proved that the Mn-Fe-Ce/ZSM-5 catalyst had relatively stable denitration performance,and the denitration efficiency reached 93.8%at 150°C.Secondly,when different volume fractions of H2O were introduced into the simulated flue gas,the denitration activity of the catalyst was reduced due to the poisoning effect of H2O.Experiments had found that the catalyst had the most superior water resistance when using ZSM-5 molecular sieve as its support.According to the molecular dynamics simulation analysis,it was found that the adsorption of H2O molecules on the active component?-MnO2 was physical adsorption,and Ce doping can inhibit the physical adsorption of H2O molecules on the active component and improved the water resistance of the catalyst.Compared to the support?-Al₂O₃ and TiO₂,ZSM-5 molecular sieve as a support can inhibit the physical adsorption of H2O molecules on its surface,making it more difficult for H₂O molecules to adsorb on its surface.In addition,when different mass concentrations of SO₂ were introduced into the simulated flue gas,the catalyst was significantly poisoned by SO₂.The experiments found that the doping of the metal element Ce in the catalyst can effectively improve the sulfur resistance of the catalyst.XRD,SEM,BET,and TG-DTG characterization of the catalyst before and after the reaction revealed that when Ce was doped in the catalyst,the reaction between SO₂ and NH₃,?-MnO₂ could be effectively inhibited,the production of ammonium sulfate and manganese sulfate was significantly reduced,the poisoning effect on the active components was reduced,and the sulfur resistance of the catalyst was effectively improved.Molecular dynamics simulation studies had found that doping Ce in the catalyst can increase the activation energy of the reaction between SO2 and?-MnO2,and inhibited the poisoning effect of SO₂ on the active components.What's more,when H₂O and SO₂ were simultaneously introduced into the simulated flue gas,the reduction rate of the denitration efficiency of the catalyst was lower than that of the H₂O and SO₂ added separately.Molecular dynamics simulations found that when SO2 and H2O molecules were present at the same time,due to the high adsorption energy of SO2 molecules,they would first be adsorbed on the surface of the active component?-MnO2,which inhibited the adsorption of H2O molecules.That was,the interaction of H2O and SO2 reduced the amount of H2O molecules adsorbed on the surface of?-MnO2,thereby reducing the poisoning effect of H2O on the catalyst.Finally,a series of honeycomb monolithic catalysts were prepared using TiO2 and ZSM-5 molecular sieves as carriers,Mn,Ce,Fe,and V as active components,and their activity tests and characterization analysis were performed.Under the experimental conditions of 500mg/m³ NO,108mg/m³ SO₂,8%O₂,10%H₂O,and space velocity4000h-1,the denitration activity of the honeycomb catalyst relative to the granular catalyst decreased.After the honeycomb catalyst was modified,the denitration efficiency of No.4honeycomb catalyst reached about 70%at 180°C.Through XRF and XRD characterization analysis,it was found that different preparation processes would have a impact on the catalyst's denitration activity.The honeycomb catalyst is oriented to practical applications.The effect of the preparation process on the performance of Ce-doped Mn-Fe catalyst for low-temperature denitrification and its improvement have yet to be systematically studied.