A Study On The Denitrification Characteristics Of Cu Ion Exchange Zeolite Supported Nb Metal Oxides At Low-temperature

There is a large quantity of NOx in the flue gas in coal-fired power plants,and the commonly used denitrification technology is SCR technology.As for traditional high-temperature SCR denitrification technology,it is prone to catalyst poisoning during the operation process,because the catalyst is placed before the dust remover and desulfurization device.For this reason,it is imperative to develop a low-temperature denitration catalyst with high denitrification performance.First of all,orthogonal experiments were used in the study to obtain the optimal optimization conditions for the preparation of catalysts.The experimental results show that among all optimization conditions of preparation,the calcination time exerts the greatest effect on the denitrification performance of the catalyst studied.Under the optimum conditions(with the calcination temperature of 550?,the calcination time of 3h,the n(Nb)/n(Cu)ratio of 0.25,and the impregnation temperature of 75?),Cu-ZSM-5 catalyst was prepared through H-ZSM-5 liquid-phase ion exchange method.Subsequently,the Nb/Cu-ZSM-5 zeolite catalyst was prepared by the equal volume impregnation method loaded with niobium metal oxide.The effects of experimental conditions on the denitrification performance of the two catalysts were investigated from single factors such as reaction temperature,the concentration of O2,the inlet concentration of NO,the air speed and the ratio of ammonia to nitrogen:n[NH3]/n[NO].Besides,the sulfur resistance of Nb/Cu-ZSM-5 was studied by adding SO2 during the experiment.The results show that for the effects of single factors in working conditions on the denitrification efficiency of Cu-ZSM-5 and Nb/Cu-ZSM-5,two kinds of zeolite catalysts,the experimental conditions that enable the conversion rate of NO reaches the maximum of 64.7%and 83.3%respectively are as follows:the oxygen concentration shall be 30ml/min,the inlet concentration of NO shall be 1000ppm,the air speed is 3000h-1 and the n[NH3]/n[NO]shall be 1.1.Finally,the sulfur resistance of Nb/Cu-ZSM-5 zeolite catalyst was tested to be dissatisfactory,by adding SO2 to the catalyst evaluation bench.At the low-temperature point of 180?,the conversion rate of NO was increased from 64.7%to about 83.3%,after the Cu-ZSM-5 zeolite catalyst is loaded with niobium metal oxide.Afterwards,the mechanism of the internal structure and catalytic activity improvement of Nb/Cu-ZSM-5 zeolite catalyst samples were studied by characterization tests like BET,SEM,XRD,NH3-TPD,XPS and FI-TR.Several factors can exert effects on the increase of the catalytic activity of Nb/Cu-ZSM-5,such as the increase of the specific surface area and micropore volume of the catalyst,the increase of the number of active sites required for the reaction between NH3 and NO,the move of the peak value of the niobium oxide peak toward the low bond energy direction,the existence of a certain amount of chemical adsorption oxygen(Ob)and the adsorption capacity of ammonia on the surface of the catalyst.