煅烧气氛对柠檬酸溶胶凝胶铁氧化物催化剂低温SCR脱硝性能的影响

Effect of calcination atmosphere on low-temperature denitrification of citric acid sol-gel iron oxide catalyst

煅烧气氛对催化剂的活性有重要影响,为了优化柠檬酸溶胶凝胶铁氧化物(Fe2O3/LA)低温烟气脱硝催化剂的制备工艺,明确煅烧气氛对Fe2O3/LA催化剂低温脱硝性能的影响规律,通过柠檬酸(LA)溶胶-凝胶法制备了Fe2O3/LA-Air和Fe2O3/LA-Ar低温脱硝催化剂,并采用N2吸附-脱附(BET)、X射线粉末衍射(XRD)、氢气升温还原(H2-TPR)、氨气升温脱附(NH3-TPD)、X光电子能谱(XPS)等对催化剂进行了表征。结果表明:Fe2O3/LA-Air催化剂与Fe2O3/LA-Ar催化剂相比高温脱硝活性较差,但具有更好的低温脱硝活性,尤其在120~200℃,其脱硝效率达80%~100%;且其N2吸附-脱附曲线呈H3型滞后环Ⅱ型等温线,具有更大的孔径;在270℃具有典型的中低温H2还原峰,中低温还原能力强;2种气氛下煅烧的Fe2O3/LA催化剂主要活性成分皆为γ-Fe2O3,且Fe2O3/LA-Air催化剂中Fe3+含量比Fe2O3/LA-Ar催化剂Fe3+含量高3.24%,表面吸附氧Oβ含量高48.24%;Fe2O3/LA-Ar催化剂中温和高温氨脱附峰均向高温方向移动,其中高温氨脱附峰面积比Fe2O3/LA-Air催化剂脱附峰面积大,Lewis酸位点数量多,但Fe2O3/LA-Air催化剂Bronsted酸位点比Fe2O3/LA-Ar催化剂多,这些因素使得空气气氛下煅烧的Fe2O3/LA催化剂低温段的脱硝活性优于氩气气氛下煅烧的Fe2O3/LA催化剂的脱硝活性。

Calcination atmosphere has an important influence on the activity of catalyst.To optimize the preparation process of citric acid sol-gel iron oxide(Fe2O3/LA)low-temperature denitrification catalyst and clarify the effects of calcination atmosphere on the low-temperature denitrification performance of Fe2O3/LA catalyst,the Fe2O3/LA-Air and Fe2O3/LA-Ar catalysts were prepared by a citric acid(LA)sol-gel method and the catalysts were characterized by N 2 adsorption desorption(BET),X-ray powder diffraction(XRD),H2 reduction by heating(H2-TPR),NH3-temperature desorption(NH3-TPD)and X-ray photoelectron spectroscopy(XPS).The results show that Fe2O3/LA-Air catalyst has poorer denitrification activity at high temperature compared with Fe2O3/LA-Ar catalyst,while it has better denitrification performance at low temperature,especially at 120-240 o C,of which the NOxconversions can reach 80-100%.And its nitrogen adsorption-desorption curve is H3 type hysteresis loopⅡtype isotherm with larger pores.The Fe2O3/LA-Air catalyst has a typical H2 reduction peak of medium and low temperatures at 270 o C,which has strong reduction capacity.The main active ingredients of the catalysts calcined at two atmospheres areγ-Fe2O3.The contents of Fe 3+and surface adsorption oxygen Oβin Fe2O3/LA-Air catalyst are 3.24%and 48.24%higher than those of the Fe2O3/LA-Ar,repectively.For the Fe2O3/LA-Ar catalyst,its peaks of ammonia desorption at moderate and high temperatures all move towards high temperature,and the peak area of ammonia desorption at high temperature is larger than that of Fe2O3/LA-Air catalyst,so there are more Lewis acid sites.However,the Bronsted acid sites of Fe2O3/LA-Air catalyst are more than those of Fe2O3/LA-Ar catalyst.These factors are responsible for that the denitrification activity of Fe2O3/LA catalyst calcined in air atmosphere at low temperature is better than that of Fe2O3/LA catalyst calcined in argon atmosphere.