Research On The Preparation And Sulfur-Poisoning Regeneration Of Sintering Gas Denox Catalysts For Low-Temperature SCR

Low-temperature selective catalytic reduction?SCR?of NOx with NH₃ is a new technology with the broad application prospects in reducing the NOx emission of sintering gas.As the key element of this technology,the low-temperature SCR catalysts still face some obstacles such as the unsatisfactory low-temperature activity and SO₂ resistance restricting its real application.In this paper,based on the modification of the traditional Mn/Ti catalysts,the denitrification performance of rare earths Ho and Nd modified Mn/Ti catalysts was tested.Simultaneously,the microstructure and physicochemical properties were studied using various characterization methods such as Brunauer-Emmett-Teller?BET?surface measurement,X-ray diffraction?XRD?,scanning electron microscope?SEM?,temperature-programmed reduction?TPR?,temperature-programmed desorption?TPD?,thermogravimetric analysisin?TPR?,in situ diffuse reflectance infrared Fourier transform spectroscopy?in situ DRIFTs?and X-ray photoelectron spectroscopy?XPS?.Then,the optimized catalyst was tested for sulfur and water resistance,and the sulfur-removing mechanism of the modified catalyst was proposed.Finally,the regeneration method of the deactivated catalyst was explored to determine an optimal regeneration method and the regeneration mechanism.Two series of Nd-modified Mn/Ti and Ho-modified Mn/Ti catalysts were prepared by impregnation method.Compined denitration activity tests with catalyst characterizations,it was found that doping of Ho₂O₃ and Nd₂O₃ could improve the low-temperature denitrification activity of Mn/Ti catalyst and widen the reaction temperature window.At 100°C,the denitration efficiency of the 0.2HoMn/Ti catalyst was about 94.46%,and the denitration efficiency was close to 100%in the temperature range of 140°C to 220°C.The modified catalyst had characteristics such as high specific surface area,strong redox ability,abundant surface acid sites and high concentration of Mn⁴⁺and surface adsorbed oxygen.The adsorption and activation ability of NH₃ and the ability of NO to oxidize NO₂ were enhanced,so that the denitration performance was improved.And,Ho modified catalysts follow the Langmuir–Hinshelwood?L-H?mechanism and the Eley–Rideal?E–R?mechanism.The SO₂ and H₂O tolerance of Ho modified catalyst was studied.It was found that Ho modification can effectively improve the sulfur resistance of the catalyst compared with Mn/Ti catalyst.In the presence of SO₂,both the L-H and E-R mechanisms of the Mn/Ti catalyst were significantly suppressed,but for the Ho-modified catalyst,SO₂ had a weaker effect on the adsorption and activation of NO on the catalyst surface,and the L-H reaction path was affected.SO₂ basically did not affect the adsorption and activation of NH₃ on the Ho modified catalyst surface.Ho-modified catalyst dominated the E-R reaction mechanism in the presence of SO₂.Therefore,the Ho-modified catalyst had good sulfur resistance.The deactivated catalyst was subjected to a water-wash regeneration experiment and a thermal regeneration experiment in a nitrogen,ammonia,and hydrogen atmosphere.The regeneration effects were as follows:water wash>N₂-350>NH₃-450>H₂-450.Ultrasonic water washing is the best for the regeneration of deactivated catalysts,and 92.4%of denitrification efficiency can be restored at 220°C.The principle of water regeneration is to remove the dissolved substances and some of the particulates on the surface of the catalyst by deionized water,thereby removing some of the substances that cause catalyst poisoning?ammonium sulfate,metal sulfates,etc.?to improve the surface morphology and microscopic properties of the catalyst.As a result,the catalyst recovers part of the denitrification activity.