Experimental Study Of Catalytic Reduction Of Nitrogen Oxides Over The Catalyst Prepared By Iron Ore Tailing

Nitrogen oxides?NO_x?are recognized as a major pollutant in the atmosphere which can cause acid rain and photochemical smog,ozone depletion and other environmental pollution problems,and people pay more attention to the pollutant in recent years.At present,for the removal of nitrogen oxides,the most widely used and most proven technology is the method of selective catalytic reduction?SCR?using transition metal or noble metal as catalyst mostly.The iron ore tailing is a major solid waste of metallurgical industries,which still contains a large number of unused metal elements,such as iron.It can not only realize the comprehensive utilization of metallurgical waste,but also have important significance for the reduction of nitrogen oxides if we can use iron ore tailing to prepare the catalyst for the catalytic reduction of nitrogen oxides.The experiment of catalytic reduction of NO was carried out by using the iron ore tailing as the main raw material of catalyst and NH₃ as the reductant.The electric heating fixed bed reactor was established and the effect of catalyst particle size,reaction temperature,calcination temperature,initial concentration of NO and O₂,space velocity,iron content,addition of MnO₂ were considered.At the same time,characterization analyses,such as LDPSA,XRF,BET,XRD,SEM,TGA of the catalyst were carried out,inactivation test and kinetic analysis of catalytic reduction of NO were also conducted.The results show that the catalyst prepared by iron ore tailing has the good performance of catalytic reduction of NO.Under the working condition that inlet gas flow rate is 600mL/min,the initial concentration of NO is 600ppm?NH₃/NO = 1?,without the presence of oxygen,the performance of catalytic reduction of NO is not very ideal when the temperature is below 300?.When the temperature continues to rise,the catalytic efficiency also increases,i.e.,54.8% at 500?,85.4% at 550? and 97.5% at 600?.The particulate diameter of the catalyst has a great effect on the catalytic efficiency.The catalytic efficiency of the catalyst with an average particle size of 10?m is about 20% higher than that with an average particle size of 300?m.It is found that calcination treatment of iron ore tailing cannot effectively improve the specific surface area.The diffraction peaks of Fe₂O₃ in the catalyst become flat or disappear when the calcination temperature is above 450 ? which leads to the decrease of the catalytic efficiency.Both the initial NO concentration and space velocity have a certain effect on the efficiency of catalytic reduction.With the increase of initial NO concentration,the catalytic efficiency decreased gradually.But this effect decreases with the increase of the reaction temperature.The catalytic efficiency decreases about 5% when the total gas flow rate increases from 600mL/min to 800mL/min.The concentration of oxygen also has great influence on the catalytic efficiency.The feeding oxygen can effectively promote the catalytic efficiency when the temperature is low?350??.The catalytic efficiency can reach about 10% when oxygen was entered,while the catalytic efficiency is only 3% without oxygen.However,it cannot continue to promote the catalytic efficiency when the concentration of O₂ is over 4%.The feeding oxygen can also inhibit the catalytic reductive reaction when the temperature is high?500??.The catalytic efficiency reduces to below 40% when oxygen was entered,while the catalytic efficiency is 55% without oxygen.It is found that the catalytic efficiency increased with the increase of iron content.But it is difficult for the catalyst to disperse onto the surface of quartz sand if the iron content is too high.It can also lead to the agglomeration of catalyst at high temperature and it causes the decrease of the catalytic efficiency.The mixture of iron ore tailing and MnO₂ powder can effectively improve the catalytic efficiency of NO.Finally,inactivation test of the catalyst was conducted.At 600?,the catalytic efficiency of iron ore tailing?2.0g?can reach 98% at first,95% after 3h,60% after 8h and over 50% after 13.5h.Chemical reaction kinetics of catalytic reduction of NO was studied.The results showed that the reaction order of NO concentration and O₂ concentration were 0.876 and 0.248,respectively and the reaction order of NH₃ was 0,the activation energy of catalytic reaction is 87.76kJ/mol.