并流沉淀法制备活性氧化铝及其热稳定性的改性研究

发布时间：2018-03-08 07:46

本文选题：并流沉淀法　切入点：γ-Al2O3　出处：《沈阳工业大学》2015年硕士论文　论文类型：学位论文

【摘要】：γ-Al2O3因其拥有较高的比表面积、适宜的孔结构和良好的表面酸性等优异性能而被广泛用作催化剂及催化剂载体。但在汽车尾气催化过程中，由于体系温度可瞬间提升至1000℃以上，导致活活性氧化铝载体发生高温相变而失去活性，因此提高活性氧化铝的高温热稳定性能具有重要的现实意义。本论文主要针对制备高性能氧化铝和活性氧化铝改性两方面内容进行研究。第一部分系统地研究了采用并流法合成活性氧化铝的反应条件，通过XRD和N2吸附脱附测试确定最优合成条件，并结合TEM、FTIR等检测手段研究最适条件下的产品性能，其次通过添加正丁醇共沸蒸馏干燥及有机物PEG(2000)、非金属元素Si和稀土元素La对活性氧化铝热稳定性的改性研究。研究结果表明：采用并流沉淀法在终点pH值为9、反应温度为70℃、老化温度为90℃、先热水后酒精洗涤的条件下制备的活性氧化铝性能最优。500℃焙烧后样品的比表面积，孔容和孔径分别为418.93m2·g-1、1.60cm3·g-1和9.60nm；经1100℃焙烧后样品的比表面积为103.61m2·g-1，其晶型依然保持为θ-Al2O3；经1200℃焙烧后样品的比表面积降低为69.64m2·g-1，晶型由θ-Al2O3部分转变为α-Al2O3。通过透射电镜分析，γ-Al2O3为纳米纤维结构，尺寸大约在10nm，经高温煅烧后，转变为纳米颗粒状结构，尺寸约为20nm，显示出了高度的分散性和热稳定性能。通过添加不同介质进行共沸蒸馏干燥实验制备高比表面积大孔容孔径的活性氧化铝。实验表明，添加正丁醇制备的样品经500℃焙烧后其比表面积达到463.80m2g-1，孔体积1.92cm3·g-1和孔径11.61nm，且经1100℃的高温煅烧后，其比表面积和孔容，，依然有109.55m2·g-1和0.81cm2·g-1。而对于添加表面活性剂PEG的活性氧化铝，其热稳定性明显高于未添加PEG的活性氧化铝，PEG可有效抑制γ-Al2O3向α-Al2O3转晶。PEG最佳添加量为1%，改性后制备的样品经500℃活化后其表面积，孔容和孔径分别为530.19m2·g-1，2.16cm3·g-1和13.93nm，经1100℃的高温煅烧后，其比表面积和孔容，依然有115.04m2·g-1和0.91cm2·g-1。通过等体积浸渍法对活性氧化铝进行不同含量的Si掺杂。研究表明，Si掺杂能明显提高活性氧化铝的热稳定性能，经1100℃的高温煅烧后，Si掺杂量达到8%时，比表面积高达161.81m2·g-1，提高了近60m2·g-1的比表面积，改性效果最好。经1200℃的高温煅烧后，Si掺杂量达到6%时，比表面积依然能保持112.53m2·g-1，且晶型仍然为θ-Al2O3。另外，我们也对γ-Al2O3纳米纤维进行了La掺杂，研究表明，当La掺杂量达到6%时，其热稳定性能最佳，1200℃高温煅烧后，其比表面积依然能保持在93.07m2·g-1。通过以上研究，采用并流沉淀法并在最佳工艺条件下，可获得具有优良性能的纳米纤维状活性氧化铝。通过合理的掺杂，可进一步提高活性氧化铝的热稳定性能。可见，优异的γ-Al2O3热稳定性能主要是由于其纳米纤维结构的高热稳定性能和元素掺杂共同作用的结果所致。
[Abstract]:Gamma -Al2O3 because of the high specific surface area, proper pore structure and surface acidity of excellent properties such as good and is widely used as catalyst and catalyst carrier. But in the automotive exhaust catalytic process, the system can instantly upgrade to the temperature above 1000 degrees, resulting in the aluminium oxide carrier alive of high-temperature phase change and lose activity therefore, to improve the heat stability of activated alumina has important practical significance. This thesis focuses on the preparation of high performance alumina and activated alumina modified two aspects were studied in this paper. The first part of the system was studied and the reaction condition flow method for the synthesis of activated alumina, determined by XRD and N2 adsorption desorption test synthesis conditions the optimal, combined with TEM, the optimum conditions of product performance testing means such as FTIR, followed by adding n-butanol azeotropic distillation drying and organic matter (2000), non PEG The modification of the thermal stability of active alumina by the metal element Si and the rare earth element La showed that:
The flow and precipitation in the end point pH value is 9, the reaction temperature is 70 DEG C, the aging temperature is 90 DEG C, alcohol washing hot water first after activated alumina prepared under optimal performance of.500 DEG C after roasting the surface area and pore size were 418.93m2, Kong Rong g-1,1.60cm3 and g-1 9.60nm; 1100 after calcining at the specific surface area of the sample was 103.61m2 g-1, the crystal remains for theta -Al2O3 is 1200 DEG C after calcination; the specific surface area of the sample is reduced to 69.64m2, g-1, -Al2O3 crystal by part into theta alpha -Al2O3. by TEM, gamma -Al2O3 nano fiber structure, the size of about 10nm, after high temperature calcination, transformed into nano granular structure, size is about 20nm, shows the dispersion and thermal stability of height.
Experiment of distillation drying preparation of high specific surface activated alumina with large pore volume and pore area of the azeotrope by adding different medium. Experimental results show that the addition of n-butanol samples prepared by calcining at 500 the specific surface area of 463.80m2g-1, pore volume of 1.92cm3 - g-1 and 11.61nm in diameter, and calcined at high temperature of 1100 DEG C, the the specific surface area and Kong Rong, still have 109.55m2 - g-1 and 0.81cm2 - g-1. for activated alumina adding surfactant PEG, its thermal stability is obviously higher than that of activated alumina was added to PEG, PEG can effectively inhibit the gamma to alpha crystal -Al2O3 -Al2O3 1%.PEG is added, the modified sample prepared by 500 C after activation of the surface area and pore size were 530.19m2, Kong Rong g-1,2.16cm3 and g-1 13.93nm, 1100 DEG C after calcination at high temperature, the surface area and Kong Rong, still have 115.04m2 - g-1 and 0.91cm2 - g-1.
By impregnation method with different content of activated alumina doped with Si. The results show that Si doping can improve the thermal stability of activated alumina, calcined at high temperature of 1100 DEG C, the Si concentration reached 8%, the specific surface area as high as 161.81m2, g-1, 60m2 and g-1 increased the specific surface area and the best modification effect. After calcination at high temperature of 1200 DEG C, Si content of 6%, can still maintain the 112.53m2 g-1 surface area, and the crystal is still 9 -Al2O3. in addition, we have gamma -Al2O3 nanofibers were doped with La, studies show that when the La concentration reached 6%, the the best thermal stability, high temperature of 1200 DEG C after calcination, it can still keep in 93.07m2 g-1. surface area
Through the above research, flow precipitation method under the optimum conditions, and using available nano fibrous activated alumina has excellent performance. Through reasonable doping, which can further improve the thermal stability of activated alumina. Thus, the main gamma -Al2O3 has excellent thermal stability if due to the interactions of nano fiber structure stability the properties of high temperature and doping results.

【学位授予单位】：沈阳工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ133.1

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