The Research Of Deactivation Mechanism And Regeneration Technology For Used Denitration Catalysts

Recently,the researches on the deactivation mechanism and regeneration of used DeNO_x catalysts,have great value to promote the energy-saving and emission reduction in the power industry.In this dissertation,the arsenic and calcium deactivation of V₂O₅-WO₃/TiO₂ catalysts have been firstly reported based on the experimental analysis and theory calculation.Furthermore,novel regeneration technology and anti-poisoning cerium-based catalyst for As and Ca poisoning catalysts have been developed respectively.The main conclusions in this research are as follows:?1?The chemical deactivation mechanism on the arsenic poisoning V₂O₅/TiO₂catalysts are related to the interaction between arsenic and vanadium,which passivates the active sites on the catalysts.With the introduction of arsenic,the BET surface area,the reducibility,the amount of the Lewis acid sites and the stability of the Br?nsted acid sites of the catalysts have been destroyed.In addition,the new As-OH sites can hardly promote catalytic performance at high temperature.?2?The deactivation degree is in correlation with the calcium content;the influence of the existing forms of calcium on the catalyst surface on the catalytic activity is following the sequence:CaCO₃>CaO>CaSO₄.The introduction of calcium not only decreases the surface area,but also transforms the amorphous WO_x into calcium tungstate phase.The existing of CO₃^2-makes the content of CaWO₄ species increase,while SO₄^2-can inhibit the formation of CaWO₄ phase on the surface of catalyst.?3?The regeneration method of alkaline calcium nitrate combining weak acid cleaning for arsenic poisoning catalysts is effective:the As removal ratio reaches 91.2%,and the activity is restored up to 80%of the original level.High-temperature hydrogen reduction regeneration shows remarkably effect:after using this method,the NO transformation frequency can be recovered to 80%no matter at low or high temperature.The 1-Hydroxy Ethylidene-1,1-Diphosphonic Acid regeneration method for Ca poisoning not only removes the calcium species on the surface,but also makes the NOx conversion reach to above 90%.Meanwhile,the regenerated catalysts have meet the requirement without further treatment.?4?After comparing the two kinds of anti-poisoning catalysts?CeO₂-WO₃ and CeO₂-MoO₃?,it can be found that arsenic influences the chemical valence of surface cerium of the CeO₂-MoO₃ catalyst;while interacts with the tungsten species of the CeO₂-WO₃catalyst.With the same As content doping,the loss of Lewis acid sites on the CeO₂-MoO₃catalyst are less than that on the CeO₂-WO₃ catalyst.?5?The CeO₂-WO₃ catalyst shows high ability for calcium resistance.Although the introduction of calcium decreases the amount of Br?nsted acid sites and their thermostability,the more adsorbed NO₂ can participate the SCR reaction.This makes up the negative effect from CaWO₄ formation and the Ce³⁺species decrease,and thus shows Ca resistant performance.