Study On Modification And Mechanism Of Mn-based Low Temperature SCR Catalyst

Selective catalytic reduction?SCR?technology is a key technology in flue gas denitrification process.The V₂O₅/TiO₂ catalyst requires a high reaction temperature,which requires the SCR device to be placed before desulphurization to avoid the repeated heating of the flue gas,which will greatly increase the cost of stripping.Therefore,it is necessary to develop low temperature??423K?SCR catalyst and process.MnOx-based catalyst displayed the best low-temperature SCR performance,which is a suitable catalyst for SCR technology.However,the activity and temperature range window of MnOx-based catalyst need to be further enhanced.At the same time,SO₂ in the flue gas can cause the catalyst deactivation.Therefore,it is necessary to study a low temperature SCR catalyst with high activity and the resistance to SO₂ on the basis of MnOx catalyst.In the paper,the transition metal elements and rare earth metal elements as additives to modified MnOx catalysts and test SCR activity and the resistance to SO₂.Moreover,a series of characterization methods were used to analyze the reaction mechanism.Firstly,the utilization of Nd as the modifier to enhance the performance of Mn-based SCR catalyst.The introduction of Nd into MnOx catalyst could greatly improve its SCR activity and its operation temperature window was also distinctly widened.Moreover,MnNdOx catalyst exhibited much higher SO₂ and H₂O resistance than MnOx catalyst.Characterization results indicated that the introduction of Nd into MnOx catalyst could enhance its reducibility and generate new active sites for NH₃ and NOx adsorption.Furthermore,the presence of Nd in Mn NdOx-0.1 catalyst had a notable activation effect on the adsorbed NH₃ and NOx species,especially at low temperature.Secondly,Sb was used as the additive to enhance the NH₃-SCR performance of MnTiOx catalyst.Experimental results revealed that MnSbTiOx demonstrated outstanding NH₃-SCR activity in a wide temperature window?100-400??and high resistance to SO₂.Characterization results proved the formation of more reducible species and the generation of more Mn⁴⁺and surface adsorbed oxygen species after the introduction of Sb into MnTiOx catalyst,which could remarkably enhance NO oxidation.Moreover,more adsorbed NH₃ and adsorbed NOx species with high reactivity could be found on the surface of MnSb TiOx catalyst.Following as an effect,the NH₃-SCR reaction over MnSbTiOx could be accelerated through the the L-H route.Thirdly,Eu was successfully used as the additive to improve its resistance to SO₂ under SCR conditions.Characterization results indicated that the addition of Eu on Mn/TiO₂ catalyst could inhibit the formation of sulfate species over it under SCR conditions,and the NH₃-SCR reaction over MnEu/Ti O₂ catalyst in the presence of SO₂ could take place through L-H pathway.Finally,Nb was used as the additive to improve the SCR activity and SO₂tolerance of Mn/TiO₂ catalyst in this study.Experimental results indicated that the MnNb/TiO₂ catalyst exhibited excellent SCR activity and SO₂-poisoning resistance compared with Mn/TiO₂ catalyst.Characterization results revealed that the presence of proper amount Nb could enhance the reducibility and surface acidity of Mn/Ti O₂ catalyst,as well as the generation of more Mn⁴⁺and chemisorbed oxygen species.The results of in situ DRIFT study demonstrated that Eley-Rideal mechanism was the chief pathway for the NH3-SCR reactions over MnNb/TiO₂ catalyst samples.When SO₂ was present in the simulated flue gas,the NH₃-SCR reactions over MnNb/TiO₂-0.12 mainly took place between adsorbed NO₂ and gaseous NH₃,which still obeyed the Eley-Rideal mechanism.