Reduction And Regeneration Of Fe(Ⅱ) EDTA Denitrification Solution By Fe/Ni Bimetallic Composite Supported On Activated Carbon

Nitrogen oxide（NO_x） is one of the main air pollutants,is an important precursor of fine particulate matter(PM_2.5),ozone and other air pollution,effective control of NOx emission is crucial to the improvement of the atmospheric environment.With the basic completion of NO_x control in thermal power industry,the efficient removal of NO_x under low temperature and complex flue gas conditions such as small and medium-sized boilers and furnaces has become the key field of NO_xcontrol.Complexation absorption denitration-zero valent iron reduction technology has become one of the best feasible technologies for low temperature complex flue gas denitration because of its mild reaction conditions,fast absorption rate,high absorption efficiency,and free from the influence of impurities such as tar and heavy metals.However,there are still some problems in this technology,such as low iron reduction rate,poor selectivity of iron reduction of nitrosyl compound N₂,and the need for subsequent treatment,which greatly restrict the application of this method.In this paper,we designed and prepared iron-supported bimetallic materials AC-Fe/Ni and Na Y-Fe/Ni,aiming at the bottleneck of low reduction rate and poor selectivity of absorption solution for reduction and denitration of elelic iron,and systematically studied the reduction performance of Fe（Ⅲ）EDTA and Fe（Ⅱ）EDTA-NO of these materials.The reaction mechanism of the reduction of denitration solution and the product regulation mechanism of selective reduction of Fe（Ⅱ）EDTA-NO were investigated by means of theoretical calculation and electrochemical analysis.The effects of carrier characteristics,p H value,oxygen concentration and other factors on reduction performance and their mechanisms were investigated.Fe-based bimetallic materials with high reducing activity and selectivity were obtained,which laid a theoretical and technical foundation for industrial application of complexation absorption denitration technology with high efficiency and high N₂ selectivity.First,the reduction of Fe（Ⅲ） EDTA by AC-Fe/Ni under near-neutral conditions was investigated,and compared with AC-n ZVI and AC-Ni.The results show that:The reduction rate constant of AC-Fe/Ni is 2.1118m M/min,which is 3 times and 2 times that of AC-nZVI and AC-Ni,respectively.The reduction efficiency of AC-Fe/Ni reaches 93% in 15min.Kinetic study and theoretical calculation show that the relative size of redox potential of elemental iron and nickel changes due to the presence of EDTA ligand in the system.In the process of Fe（Ⅲ）EDTA reduction by AC-Fe/Ni,the main electron donor is not Fe⁰,but Ni⁰.The kinetics of Fe（Ⅲ）EDTA reduction is similar to that of AC-Ni.The reduction rate of the bimetallic materials is significantly improved,which is mainly attributed to the multi-component micro-electrolysis system constructed by the bimetallic materials and activated carbon.A variety of galvanic cells,such as Fe-C,Ni-C and Fe-Ni,have greatly enriched the electron acquisition pathway of Fe（Ⅲ）EDTA,greatly promoted the electron transfer,and weakened the competition of iron oxide on the surface active site,thus improving the reductive activity of the material.The experimental results show that the reduction of Fe（Ⅲ）EDTA by AC-Fe/Ni is affected by the p H value of the solution,the initial concentration of Fe（Ⅲ）EDTA and the concentration of O₂.When the oxygen content is 10%,AC-Fe/Ni can still effectively reduce Fe（Ⅲ）EDTA,which is expected to be applied in industrial practice.Then,the reduction of Fe（Ⅱ） EDTA-NO by bimetallic nanomaterials AC-Fe/Ni supported on activated carbon under near-neutral conditions was investigated,and compared with the reduction of Fe（Ⅱ）EDTA-NO by AC-nZVI and AC-Ni,the results show that:The reduction efficiency of AC-Fe/Ni was 96.02%,and the reaction rate constant was 0.11213 min^-1,which was 1.5 times and 3 times of that of AC-n ZVI and AC-Ni.The performance advantage of bimetallic materials is mainly due to its multi-microelectrolytic system,which provides more active sites for the adsorption and enrichment of Fe（Ⅱ）EDTA-NO,enriches the reaction pathway,and improves the reduction effect very highly.Moreover,a large number of strong reducing agent--active hydrogen can be generated to further promote the reduction of Fe（Ⅱ）EDTA-NO.By comparing the selectivity of Fe（Ⅱ）EDTA-NO reduction products,the highest N₂ selectivity was obtained by AC-Fe/Ni with 74.87%.Crucially,the addition of a second metal,Ni,gives it a stronger microelectrolysis and produces more adsorbed hydrogen.However,hydrogen adsorption can strongly capture the oxygen atom on Fe（Ⅱ）EDTA-NO,thus changing the reduction path of Fe（Ⅱ）EDTA-NO,promoting N-N recombination to generate N₂ and obtaining high N₂selectivity.The multiple microelectrolysis of AC-Fe/Ni provides various potentials for Fe（Ⅱ）EDTA-NO reduction reaction,and provides more possibilities for the high N₂selectivity of the reaction products.At low pH,the larger electrode potential difference makes Fe（Ⅱ）EDTA-NO gain more electrons at a faster rate,which leads to higher reduction efficiency and faster reduction rate.The initial pH value affects the selectivity of the product,because the increase of p H weakened the micro-electrolysis effect and reduced the generation of H_ad,but at the same time,the increase of Fe（Ⅱ）EDTA-NO/H ratio in the solution also promoted the N-N binding and promoted the product to produce more N₂.Finally,in order to investigate the effect of the carrier on the reduction activity of bimetallic materials,the reduction of Fe（Ⅱ）EDTA-NO and Fe（Ⅲ）EDTA by Na Y-Fe/Ni and AC-Fe/Ni were investigated under near-neutral conditions.The reduction rate of Fe（Ⅱ）EDTA-NO by AC-Fe/Ni(0.11213min^-1)was 10 times higher than that of Na Y-Fe/Ni,but the N₂ selectivity of both was approximately the same.For Fe（Ⅲ）EDTA,the reduction efficiency of AC-Fe/Ni was higher（93%）than that of NaY-Fe/Ni（74.17%）.The reduction rate of NaY-Fe/Ni was 0.4493m M/min,while the reduction rate of Fe（Ⅲ）EDTA（2.112 m M/min）by AC-Fe/Ni was about 5 times higher than that of Na Y-Fe/Ni.The faster reduction rate of AC-Fe/Ni can achieve higher reduction efficiency.Due to the similar specific surface area of Na Y-nZVI and AC-Fe/Ni,the metal nanoparticles on NaY-nZVI and AC had similar particle sizes,showing uniform distribution and high dispersion morphology.This indicates that the significant difference in the reduction activity of the two kinds of bimetallic materials supported by the carriers is not reflected in the influence of the carriers on the particle size and forming of the materials,but due to the participation and promotion of the carriers themselves in the reduction reaction.Through cyclic voltammetry experiments,it is shown that activated carbon has larger charge capacitance,which makes it have higher charge transport efficiency and faster electron transport speed.Compared with NaY-Fe/Ni,the electron transfer rate of AC-Fe/Ni in galvanic cells is faster,which makes the micro-electrolysis reaction proceed at a faster rate,thus promoting the reduction and regeneration of Fe（Ⅱ）EDTA denitration solution.