Study On The Low Temperature NH₃-SCR Performance And Denitration Mechanism Based On Density Functional Theory Over Cu-HPMo/TiO₂ Heteropolyacid Catalyst

Low-temperature industrial flue gas represented by the iron and steel industry is an important source of nitrogen oxide(NO_x)emissions,and ammonia selective catalytic reduction(NH₃-SCR)is the most mature technology for controlling stationary source NO_x emissions.In view of the biological toxicity of commercial vanadium-tungsten-titanium catalysts,low catalytic activity and poor SO₂&H₂O resistance when used in the iron and steel industry flue gas.This paper studied the preparation of a Ti O₂-supported copper-phosphomolybdic acid low-temperature denitrification catalyst(Cu-HPMo/Ti O₂),tested the effect of preparation and process parameters on the NH₃-SCR performance,and analyzed its sulfur and water resistance and physical and chemical properties.In addition,in-situ diffuse reflectance infrared fourier transform spectroscopy(In-situ DRIFTs)and density functional theory(DFT)methods were used to investigate the adsorption and transformation process mechanism of reactants on the catalyst surface sites,which provided a theoretical reference for improving the NH₃-SCR performance of low-temperature denitration catalysts.The NH₃-SCR performance results showed that Cu-HPMo/Ti O₂ catalyst had the best denitrification efficiency when the molar ratio of Cu/Mo was 3,the amount of CTAB was 20%,the loading amount of active component was 10%,the calcination temperature was 350?,the O₂ content was 6-12 vol.%,the NH₃/NO ratio was 1 and the space velocity was 15000 h^-1,and the NO_x conversion rate could be maintained above 99%in the range of 200-350?.The Cu-HPMo/Ti O₂ catalyst showed good sulfur resistance due to the strong surface acidity of HPMo could inhibit the SO₂adsorption.But the catalytic activity was inhibited to a certain extent when the SO₂concentration was 600 ppm.The characterization results showed that HPMo and CuO were the active crystal phases of the catalyst.CTAB addition increased the specific surface area of the active component,improved the dispersion of the active component,and optimized the morphology of the active component CuO.Cu and CTAB addition also improved the redox performance and NO treatment capacity of the catalyst at low temperature.The DFT calculation results showed that SO₂ was only physically adsorbed on the surface of HPMo cluster,NO,NH₃ and H₂O formed chemical adsorption on the acidic sites on the surface of HPMo cluster and CuO(1 1 1)supercell.The adsorption capacities of SO₂ and H₂O were generally weaker than that of NH₃ and NO.The NH₃-SCR reaction of NO and NH₃ on the surface of HPMo clusters and CuO(1 1 1)supercells follows this process:*-NH₃?*-NH₂(or*-NH₄⁺)?*-NH₂+NO(or*-NH₄⁺+NO)?*-NH₂NO?*-HNNOH?*-N₂+H₂O?*-H(*represents the surface site of the active component).Four transition states were required during the reaction:NH₃dissociation,amide formation,internal hydrogen transfer and atom isomerization.Integrating the results of In-situ DRIFTs and the energy barrier value corresponding to each transition state,the NH₃-SCR reaction of Cu-HPMo/Ti O₂ catalyst has both E-R and L-H mechanisms.Among them,the reaction on HPMo tends to follow the L-H mechanism,while the reaction on CuO is more likely to follow E-R mechanism.