【作者】 冯英；

【导师】 宋永吉；

【作者基本信息】 北京化工大学 ， 化学工程与技术， 2011， 硕士

【摘要】 氮氧化物(NOx)是大气的主要污染物之一,对生态环境、经济发展及人体健康具有很大的危害。氮氧化物的种类较多,造成大气污染的主要有NO.N02和少量的N20。目前,N20的有效消除方法为催化分解；而NO的脱除常用选择性催化还原法(SCR)。六铝酸盐型催化剂在高温下稳定性较好,且催化活性较高,近年来得到广泛性研究。本文采用共沉淀法制备了一系列不同金属掺杂的六铝酸盐型脱硝催化剂；同时,制备了以六铝酸盐作为载体,采用等体积浸渍法制备的铁负载型催化剂。通过XRD.H2-TPR、BET.TG-DSC等手段,对所制备的催化剂进行了结构、物性表征,采用微型反应装置研究了该系列催化剂脱除NOx的反应活性。(1)实验研究了六铝酸盐催化剂催化分解N20的性能。掺杂Cu、Co的Ba系六铝酸盐BaMxAl12-xO19-δ(x=1,2,3,4)的晶体结构较复杂,生成了较多的尖晶石晶相,且催化分解N20的活性较差。实验发现BaCoxAl12-xO19-δ催化分解N20的过程中产生了较大浓度的NO,高达1000ppm。La系六铝酸盐具有较好的N20催化分解性能。LaCuAl11O19-δ具有较单一的六铝酸盐晶体结构,且催化分解N20的活性较高。以LaCuAl11O19-δ为基础,复合掺杂第二金属元素Mn.Fe后,形成的LaCuxM1-xAl11O19-δ(X=0.2,0.4,0.6,0.8)催化剂,催化分解N20的活性较高,且在一定程度上降低了尾气中NO的浓度。尝试在LaCu0.4Fe0.6Al11O19-δ催化分解N20的过程中加入还原气CH4,发现其加入不仅提高了N20的转化率,还降低了NO的生成浓度。(2)实验研究六铝酸盐催化剂在CH4气氛下催化还原NO的性能。采用共沉淀法制备LaMAl11O19-δ催化剂,以碳酸铵为沉淀剂,样品在60℃下老化3h,1200℃下焙烧4h后制得催化剂样品。表征结果表明,不同离子掺杂型六铝酸盐LaMAl11O19-δ催化剂中,M为Mn、Cu、Fe时,催化剂形成了较完整的六铝酸盐晶相,比表面积较大,催化活性表现较佳。实验结果表明Mn、Cu的最佳掺杂量为1,Fe的最佳掺杂量为2。双金属掺杂型六铝酸盐经1200℃焙烧4h后,仍具有明显的六铝酸盐结构。与单金属Mn、Fe掺杂的催化剂相比,LaMnCuAl10O19-δ和LaFeCOAl10O19-δ的催化活性有了明显提高。LaCuxFe1-xAl11O19-δ系列催化剂中,x=0.8时催化剂的活性最好,且活化能较低(为90.52kJ·mol-1)。(3)实验研究六铝酸盐负载铁氧化物催化剂在CH4气氛下催化还原NO的反应活性。采用等体积浸渍法制备的3wt%Fe2O3/LaAl12O19-δ催化剂,在600℃下焙烧4h后,硝酸铁氧化分解形成了高分散型Fe2O3,并附着在载体的表面上。该催化剂的比表面积较大,催化活性较高(T10%为490℃,T90%为589℃)。连续100h的高温稳定性实验表明,六铝酸盐负载铁的催化剂具有较好的抗热性。更多还原

【Abstract】 Nitrogen oxides (NOX) are very important pollutants in the atmosphere, which have great harmful effect on ecological environment, economic development and human health. There are many types of NOX, but air pollution mainly caused by NO, NO2, and N2O. Currently, catalytic decomposition is an effective way to remove N2O, which usually is a by-product in petrochemical industry. Selective catalytic reduction (SCR) method is often used to remove NO in the flue gas of coal combustion power plant. Hexaaluminate catalyst has been extensively researched in recent years because it is a kind of high thermal stability catalyst materials with higher catalytic activities under high temperature environment.In this paper, a series of transit metal-doped hexaaluminate catalysts were prepared by co-precipitation. And hexaaluminate-supported Fe2O3 catalyst has been prepared by incipient wetness impregnation method. The catalysts were characterized by XRD, H2-TPR, BET, TG-DSC and other means. The catalytic denitrification activities of the samples were examined in a miniature reaction rig. (1) The performances of hexaaluminate catalysts for N2O direct decomposition were studied.Ba series hexaaluminates BaMxAl12-xO19-δ(M=Cu, Co; x=1,2,3,4), were prepared. These compound crystal structure was much complex and their catalytic activity was poor. At the same time, experimental results showed that there was a great amount of NO in the decomposition products when N2O decomposition over BaCoxAl12-xO19-δcatalyst, which concentration was up to 1000ppm.La series of hexaaluminate catalysts expressed advanced N2O direct decomposition activity. Perfect hexaaluminate phase was found in LaCuAl11O19-δcatalyst, which also had better activity for N2O decomposition. LaCuxM1-xAl11O19-δ(x=0.2,0.4,0.6,0.8) was prepared by doping metal elements Mn and Fe in Cu-doped hexaaluminate. Their activities of N2O decomposition were higher than single Cu doped hexaaluminate and NO concentration in the exhaust gas decreased at some extent. When CH4 was added in the process of N2O decomposition over LaCu0.4Fe0.6Al11O19-δ, conversion rate of N2O was increased and the concentration of by-product NO was decreased ulteriorly.(2) NO catalytic reduction activities were studied over hexaaluminate under CH4 atmosphere.LaFeAl11O19-δwas prepared by co-precipitation with ammonium carbonate as precipitant. The precursor was precipitated at 60℃for 3h and then was calcinated at 1200℃for 4h. The characterized results showed that LaMAl11O19-δ(M was Mn, Cu and Fe) expressed perfect hexaaluminate phase and the catalyst samples had higher catalytic activity. The results showed that the optimal doping amount of Mn, Cu and Fe is 1,1 and 2, respectively.Bi-metal doped catalysts LaMMAl10O19-δwere also formed complete hexaaluminate phase under calcinated at 1200℃for 4h. They showed high specific surface area and good catalytic activity. Comparison with single Mn or Fe-doped catalysts, catalytic activities of LaMnCuAl10O19-δand LaFeCoAl10O19-δhad significantly improved. In the series of LaCuxFe1-xAl11O19-δsamples, the catalyst with x=0.8 had a better activity for N2O decomposition and its activation energy was about 90.52 kJ·mol-1.(3) Investigation on NO catalytic reduction over hexaaluminate supported iron catalysts.Incipient wetness impregnation method was employed to prepared 3wt% load Fe2O3 on LaAl12O19-δcatalyst. The precursor was calcinated at 600℃for 4h to form a high dispersed Fe2O3 on the hexaaluminate carrier surface with a higher specific surface area. Experiment of NO reduced reaction with CH4 as reductant showed that the catalyst catalytic activity was excellent, which temperature of T10% and T90% were 490℃and 589℃, respectively.100 hours continuous lifetime experiment indicated that no obvious activity decline was observed.更多还原