The Preparation Of Denitration Catalysts For Coking Flue Gas And Performance Research

With the vigorous development of the domestic coking industry,the contribution of NO_x emissions from the coking flue gas is increasing to the total NO_x emissions.In the recent years,the importance of coking flue gas denitration has drawn great attention in China.But the traditional SCR?selective Catalytic Reduction?catalysts applied to coal-fired flue gas can't adapt to the denitration conditions demand of the coking flue gas because of the low temperature and reducing sulfide in coking flue gas.According to the actual situation of the coking flue gas,this study put forward the layered multiple effect SCR technology which is suitable for coking flue gas denitration,realizing the coordinated control of NO_x and H₂S pollutants.For the first layer of the catalyst,we use the strong oxidizing high vanadium catalyst for denitration as well as decomposition of hydrogen sulfide.Choosing nano titanium dioxide as the carrier,a series of V/Mo-Ti catalysts were made using the impregnation method.The results showed that when the temperature was higher than 250?,2V/4Mo-Ti showed the best denitration efficiency and high N₂ selectivity.The performance of the V/Mo-Ti catalyst for the catalytic oxidation of H₂S was investagited and the results showed that V had a strong ability to the catalytic oxidation of H₂S.The H₂S conversion rate reached 100%with V containing catalysts in higher than 150?,and the products were mainly composed of SO₂.The influence of H₂S and water was studied on different catalysts.Compared with 4Mo-Ti and 2V-Ti,the denitration efficiency and resistance of H₂S of2V/4Mo-Ti catalyst were improved significantly,so it could be used in the coking gas denitration process.The hydrogen sulphide was decomposed by the upper catalyst which can reduce the toxicity for the lower catalyst.However V was still one of the toxic elements,it was a high risk for environment using the high vanadium catalysts.So the V-Mo/Ti catalyst was doped and modified to prepare a kind of low vanadium,low toxic SCR catalyst through impregnation method.Influence of modified elements,Ce loadings,space velocity and flue gas composition on the denitration efficiency was investigated.The results showed that 0.3V10Ce/4Mo-Ti had the highest denitration activity,N₂ selectivity and NH₃ conversion.Sulfur resistance test showed that the H₂S,SO₂ and water in coking flue gas can cause adverse effects to denitration activity at 200?,the above mentioned components had less effect on the denitration activity,when the temperature was greater than 250?.100 mg/m³ H₂S,100 mg/m³SO₂ and4%water were added to the simulated flue gas and running 8 h,the denitration efficiency remained above 70%.The catalysts were characterized by XRD,BET,XPS,and H₂-TPR methods.The mid-low temperature SCR mechanism of modified V/Mo-Ti catalysts and the influence of experimental conditions were further discussed.The mechanism of the SCR reaction processes on the surface of the catalysts were studied using the in situ diffuse reflection Fourier transform infrared spectroscopy?in situ DRIFT?.The results showed that the number and intensity of B acid were obviously increased after Ce doping,the surface oxygen concentration and NO oxidation performance also increased.The adsorption species and SCR activity of ammonia were greatly increased.We speculated that the SCR reaction on the surface of the catalysts mainly obeyed the Eley-Rideal mechanism.