Cu-Mn改性分子筛催化剂制备及柴油车尾气SCR脱硝基础研究

发布时间：2018-05-20 05:10

本文选题：柴油车尾气 + Cu-Mn共负载　；参考：《浙江工商大学》2015年硕士论文

【摘要】：柴油车尾气排放的氮氧化物(NOx)己成为我国大气的主要污染源之一,是造成灰霾、酸雨和光化学烟雾污染的重要原因。目前对于柴油车排放NOx的控制仍基于选择性催化还原(SCR)技术。但柴油车尾气中含有高浓度的氧气、水蒸气及烃类物质,使得传统用于处理汽油车尾气的三效催化剂不能有效地应用于柴油车尾气脱硝。分子筛由于其独特的结构、较好的吸附性能和较高的稳定性日益受到人们的关注。以分子筛作为载体的NH3-SCR催化剂应用受到广泛的研究。本文利用Cu、Mn共负载于ZSM-5和SAPO-34分子筛,研究其在柴油车尾气脱硝中的SCR活性和稳定性。本文首先对Cu-Mn共负载ZSM-5的制备参数进行了研究,发现以Cu(CH3COO)2和Mn(CH3COO)2为金属前驱体、离子交换法为制备方法、Cu/Mn摩尔比为3：2时制备的Cu-Mn/ZSM-5在转化NOx时表现出最佳的NH3-SCR活性。Cu-Mn共负载提高了Cu/ZSM-5在低温下的活性,且能保持催化剂的高温活性。但Cu-Mn/ZSM-5的水热稳定性较差,750℃水热处理24小时会使催化剂在整个温度窗口的活性下降。水热处理后Cu-Mn/ZSM-5发生团聚现象,但没有发生脱铝和结构变化,催化剂中八面体配位Cu2+含量明显下降。Cu-Mn/ZSM-5的抗烃类性能也较差,当反应气体中加入2000 ppm的C3H6后,对NOx的转化率明显下降。反应后催化剂发生团聚,且催化剂的比表面积和孔容明显下降；反应后Cu+/Cu2+明显升高,表明反应后Cu离子向低价态转化,Cu2+减少。在水热处理和抗烃类反应中,Cu2+含量的减少是催化剂活性下降的重要原因。针对Cu-Mn/ZSM-5较差的水热稳定性和抗烃类性能,本文又选取了具有CHA微孔结构的SAPO-34做为载体,进行Cu-Mn共负载。发现以Cu(CH3COO)2和Mn(CH3COO)2为金属前驱体、离子交换法为制备方法、Cu/Mn摩尔比为3：2时制备的Cu-Mn/SAPO-34在转化NOx时表现出最佳的NH3-SCR活性。Cu-Mn共负载能明显提高催化剂低温活性,200℃时Cu-Mn/SAPO-34对NOx的转化率达到了90%,比Cu/SAPO-34提高约60%,并保留了较好的中高温段活性。Cu和Mn的负载并不会改变SAPO-34的形貌和晶体结构；Cu-Mn共负载能够提高Cu的负载量和反应活性位(Cu+和Cu2+),从而提高Cu/SAPO-34低温催化活性；Cu-Mn共负载还提高了催化剂的表面酸度,从而使Cu-Mn/SAPO-34吸附更多的NH3和NO,生成反应中间体。Cu-Mn/SAPO-34具有较好的温度耐受性和水热稳定性,水热处理不会使催化剂对NOx的转化率有明显下降,240℃以下对NOx的转化率反而有所提高。水热处理后Cu-Mn/SAPO-34的晶体结构和表面形貌基本保持不变,且未产生团聚和脱铝现象,催化剂表面与八面体配位的Cu2+含量升高,是催化剂低温活性升高的重要因素。Cu-Mn/SAPO-34具有较好的抗烃类性能,反应后催化剂表现出较好的分散性和结构稳定性,催化剂比表面积虽然有所下降,但孔容和平均孔径基本保持不变,说明CHA微孔结构有效的阻挡了C3H6进入到结构内部,保护了反应活性位,使Cu-Mn/SAPO-34具有较好的抗烃类性能。
[Abstract]:Nitrogen oxides (NOx) from diesel exhaust emissions have become one of the main sources of pollution in the atmosphere of our country. It is an important cause of haze, acid rain and photochemical smoke pollution. At present, the control of NOx for diesel vehicle emission is still based on the selective catalytic reduction (SCR) technology. But the exhaust of diesel vehicle contains high concentration of oxygen, water vapor and hydrocarbons. The three effect catalyst used in the treatment of gasoline vehicle exhaust can not be effectively applied to the exhaust gas denitrification of diesel vehicle. Molecular sieves are attracting more and more attention because of their unique structure, good adsorption performance and high stability. The application of NH3-SCR catalyst with molecular sieve as a carrier is widely studied. This paper uses Cu, Mn A total of ZSM-5 and SAPO-34 molecular sieves were loaded to study the SCR activity and stability of the diesel vehicle tail gas denitrification. Firstly, the preparation parameters of Cu-Mn co loaded ZSM-5 were studied. It was found that Cu (CH3COO) 2 and Mn (CH3COO) 2 were metal precursors, the ion exchange method was a preparation method, and Cu/Mn mole ratio was the Cu-Mn/ZSM-5 in 3:2 time. The best NH3-SCR activity.Cu-Mn co loaded with NOx increased the activity of Cu/ZSM-5 at low temperature and maintained the high temperature activity of the catalyst. But the thermal stability of Cu-Mn/ZSM-5 was poor. The activity of the catalyst at 750 C for 24 hours would decrease the activity of the catalyst at the whole temperature window. After hydrothermal treatment, the aggregation of Cu-Mn/ZSM-5 was not. There is dealuminum and structural change, the content of the eight complexing Cu2+ in the catalyst decreases obviously and the anti hydrocarbon property of.Cu-Mn/ZSM-5 is also poor. When the reaction gas is added to 2000 ppm, the conversion rate of NOx is obviously decreased. The catalyst will be reunited after the reaction, and the specific surface area and pore volume of the catalyst decrease obviously, and the Cu+/Cu2+ is obvious after the reaction. It is shown that the Cu ion conversion to low valence state and Cu2+ decrease after the reaction. In hydrothermal treatment and anti hydrocarbon reaction, the decrease of Cu2+ content is an important reason for the decrease of catalyst activity. In view of the poor hydrothermal stability and anti hydrocarbon properties of Cu-Mn/ZSM-5, this paper also selects SAPO-34 with CHA micropore structure as the carrier and carries out Cu-Mn co loading. It was found that Cu (CH3COO) 2 and Mn (CH3COO) 2 were metal precursors and ion exchange was used as a preparation method. The optimum NH3-SCR active.Cu-Mn co loading of Cu-Mn/SAPO-34 in NOx when Cu/Mn mole ratio was 3:2 could significantly increase the activity of the catalyst at low temperature. The conversion rate of Cu-Mn /SAPO-34 to 90% was reached at 200. High about 60%, and retained the better load of active.Cu and Mn in the middle high temperature segment, and will not change the morphology and crystal structure of SAPO-34; Cu-Mn co load can increase the load and reactive potential of Cu (Cu+ and Cu2+), thus improve the catalytic activity of Cu/SAPO-34 at low temperature; Cu-Mn Co load also improves the surface acidity of the catalyst, thus making Cu-Mn/SAPO so that Cu-Mn/SAPO is a catalyst. -34 adsorbs more NH3 and NO, and the reaction intermediate.Cu-Mn/SAPO-34 has better temperature tolerance and hydrothermal stability. Hydrothermal treatment will not reduce the conversion of NOx obviously, and the conversion rate of NOx below 240 C is improved. The crystal structure and surface morphology of Cu-Mn/ SAPO-34 are basically maintained after hydrothermal treatment. The Cu2+ content of the catalyst surface and the eight surface body is increased, which is an important factor for the increase of the catalyst's low temperature activity..Cu-Mn/SAPO-34 has better hydrocarbon resistance. The catalyst shows good dispersion and structural stability after the reaction. Although the surface area of the catalyst is decreased, the pore volume and the pore volume are the same. The average pore size remained the same basically, indicating that the CHA microporous structure effectively blocked the entry of C3H6 into the structure, protected the reactive active sites and made Cu-Mn/SAPO-34 have better hydrocarbon resistance.
【学位授予单位】：浙江工商大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：X734.2;O643.36

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