稀土复合氧化物的合成、表征及其对甲硫醇催化分解性能的研究

发布时间：2018-05-24 05:59

本文选题：甲硫醇 + 催化分解　；参考：《昆明理工大学》2017年博士论文

【摘要】：甲硫醇(CH3SH)是一种典型的含硫挥发性有机污染物(SVOC),其来源广泛,具有较强的毒性和挥发性,直接排放到大气中,会对自然环境和人体健康造成一定危害,因而开展甲硫醇尾气的治理和减排研究工作具有重要的现实意义。本论文主要合成系列铈基稀土复合型氧化物及稀土氧化物改性复合型分子筛催化剂,进行甲硫醇气体催化分解的研究。通过对合成的催化剂进行相关表征,详细探究甲硫醇催化分解反应过程及反应机理。主要结果归纳如下:(1)利用微波辅助溶胶-凝胶法快速合成纳米颗粒Ce02催化剂,将其应用于甲硫醇的催化分解反应研究。研究表明,相比于传统溶胶-凝胶法,该方法合成的催化剂具有较多的氧空位和较小的晶体粒径,可为催化转化甲硫醇反应提供较多的反应活性位点,因而表现出良好的甲硫醇催化转化反应活性。通过对合成条件(焙烧温度、焙烧时间、铈盐与柠檬酸的配比以及微波处理时间等)进行优化,获得高性能的催化剂材料。通过对比分析反应前后催化剂的变化情况,探究氧化铈催化剂催化分解甲硫醇过程中的失活原因。其中氧化铈催化剂催化分解甲硫醇反应过程中,易消耗催化剂上的表面晶格氧,导致低价态铈硫物种(如Ce2S3)的累积,引起催化剂失活。在此基础上,对失活的催化剂进行再生处理,结果表明,失活的催化剂在450℃反应条件下通过空气处理,可在较短的时间内(10 min)恢复其原来性能,论文研究中还分析了该催化剂的再生反应过程。(2)在氧化铈催化剂研究基础上,通过向氧化铈中添加系列稀土(Y,Gd,Sm,Nd和La),合成铈基稀土复合氧化物。不同稀土的添加对合成的催化剂碱性强度及氧空位含量等性能有着不同的影响作用,并最终影响其催化分解甲硫醇的性能。其中,氧化铈中掺杂较小离子半径的稀土元素(Y和Gd等)时,合成的催化剂碱性强度得到适度的增强,氧空位浓度显著增加,晶格氧迁移能力增强,因而其催化分解甲硫醇的反应稳定性能得到改善:而氧化铈中掺杂较大离子半径的稀土元素(Nd和La等)时,一方面由于合成的复合氧化物晶胞参数增大,导致催化剂晶格的过度扭曲,使得其氧空位含量降低,另一方面较大离子半径的金属元素结合更多的阴离子氧,使得催化剂上含有更多的碱性位点,从而导致催化剂上吸附累积更多的酸性含硫物种,引起催化剂的失活。(3)为了进一步分析稀土的掺杂对氧化铈基催化剂性能的影响。论文中详细分析了铈-钇(Ce-Y)稀土氧化物的氧空位浓度及其晶格氧迁移转化过程,并将该性质与甲硫醇催化分解反应的活性进行关联。结果表明,随着稀土 Y添加量的增加,合成的催化剂的表面晶格氧含量降低,其催化分解甲硫醇活性下降,说明晶格氧含量对其催化分解甲硫醇的活性有着重要的影响作用。而Ce0.75Y0.25O和Ce0.5Y0.5O催化剂催化分解甲硫醇的稳定性能优于Ce02,主要是由于Y添加的稀土复合氧化物中含有较多的氧空位,有利于催化剂中晶格氧的迁移转化,反应过程中,更多的体相晶格氧迁移补充反应过程中消耗的表面晶格氧,继续为反应提高活性氧位点,铈基催化剂的氧迁移转化过程(体相晶格氧向表面晶格氧的迁移)对维持催化剂的表面活性氧位点、提高催化剂的稳定性能有着重要的作用。(4)探究稀土的添加对HZSM-5沸石分子筛的酸碱性的调控作用及其对催化剂催化性能的改善作用。Ce、Pr、Nd和Sm改性的HZSM-5沸石分子筛催化剂催化分解甲硫醇时,反应活性均有一定程度提高,其中Sm改性的HZSM-5分子筛表现出最佳的反应活性。一方面,稀土 Sm添加后,HZSM-5中的碱性增强,有利于酸性甲硫醇气体分子的吸附和活化,从而提高了催化剂的反应活性;另一方面,HZSM-5中添加稀土 Sm,可部分取代沸石分子筛中的骨架铝物种,使催化剂上的B酸量降低,强酸性活性位点数量减少,反应过程中有利于减少积碳的产生,进而显著提高了催化剂催化分解甲硫醇的反应稳定性能。开展稀土改性HZSM-5沸石分子筛催化剂的失活原因及再生过程研究,结果表明,积碳的累积是导致HZSM-5沸石分子筛催化剂失活的主要原因,失活的催化剂在550℃的空气中可以较容易实现多次再生。
[Abstract]:Methyl mercaptan (CH3SH) is a typical sulfur containing volatile organic pollutant (SVOC). It has a wide range of sources and has strong toxicity and volatility. It is directly discharged into the atmosphere and will cause certain harm to the natural environment and human health. Therefore, it is of great practical significance to carry out the research on the treatment and emission reduction of methyl thiol tail gas. Synthesis of a series of cerium based rare earth complex oxides and rare earth oxide modified composite zeolite catalysts for catalytic decomposition of methyl mercaptan is carried out. The catalytic decomposition process and reaction mechanism of methyl mercaptan are investigated in detail through the related characterization of the synthesized catalysts. The main results are as follows: (1) the use of microwave assisted sol - The rapid synthesis of nano particle Ce02 catalyst by gel method is applied to the catalytic decomposition of methyl mercaptan. The study shows that the catalyst has more oxygen vacancy and smaller crystal size than the traditional sol-gel method, which can provide more reactive sites for catalytic conversion of methyl thiol reaction. A high performance catalyst was obtained by optimizing the synthesis conditions (roasting temperature, calcination time, the ratio of cerium salt with citric acid and microwave treatment time) to obtain high performance catalyst materials. By comparing and analyzing the change of the catalyst before and after the reaction, the catalytic decomposition of methyl mercaptan over the cerium oxide catalyst was studied. In the process of catalytic decomposition of methyl mercaptan, cerium oxide catalyzes the breakdown of the surface lattice oxygen on the catalyst, resulting in the accumulation of low valence cerium and sulphur species (such as Ce2S3) and the deactivation of the catalyst. On this basis, the reactivation of the deactivated catalyst is regenerated. The results show that the deactivated catalyst is at 450 centigrade reaction strip. The original performance of the catalyst can be recovered in a short time (10 min) by air treatment. In the paper, the regeneration process of the catalyst is also analyzed. (2) on the basis of the cerium oxide catalyst, a series of rare earth compounds (Y, Gd, Sm, Nd and La) are added to the cerium oxide to synthesize the cerium based rare earth compound oxide. The properties of the catalyst, such as the alkaline strength and the oxygen vacancy content, have different effects and ultimately affect the catalytic decomposition of methyl mercaptan. In the case of rare earth elements (Y and Gd) doped with smaller ionic radius in cerium oxide, the alkaline strength of the synthesized catalyst is enhanced, the oxygen vacancy concentration is significantly increased, and the lattice oxygen migration is increased. As a result, the stability of the catalytic decomposition of methyl mercaptan is improved. While the rare earth elements (Nd and La) doped with the larger ionic radius of the cerium oxide, on the one hand, the crystal lattice of the catalyst is excessively twisted because of the increase of the composite oxide cell parameters, which makes the oxygen vacancy content reduced and the other is the larger ion. The metal element of the radius combined with more anionic oxygen makes the catalyst contain more basic loci, which leads to the accumulation of more acidic sulfur species on the catalyst and the deactivation of the catalyst. (3) in order to further analyze the effect of rare earth doping on the performance of the cerium oxide based catalyst. The paper detailed analysis of the cerium yttrium (Ce-Y The oxygen vacancy concentration and the lattice oxygen migration and transformation process of the rare earth oxides are associated with the activity of the catalytic decomposition reaction of methyl mercaptan. The results show that the surface lattice oxygen content of the synthesized catalyst decreases with the increase of the addition of rare earth Y, and the catalytic decomposition of methyl mercaptan decreases. The decomposition of methyl mercaptan has an important effect. The catalytic decomposition of methyl mercaptan by Ce0.75Y0.25O and Ce0.5Y0.5O catalysts is better than that of Ce02. It is mainly due to the presence of more oxygen vacancies in the rare earth compound oxides added by Y, which is beneficial to the migration and transformation of the MICROTEK lattice oxygen in the catalyst, and more bulk phase lattice oxygen in the reaction process. The surface lattice oxygen consumed in the supplementary reaction process continues to increase the reactive oxygen site, and the oxygen migration and transformation process of the cerium based catalyst (the migration of the lattice oxygen to the surface lattice oxygen of the body phase) plays an important role in maintaining the surface active oxygen site of the catalyst and improving the stability of the catalyst. (4) to explore the addition of rare earth to HZSM- The effects of the acidity and alkalinity of 5 zeolite molecular sieves and the improvement of the catalytic performance of the catalyst.Ce, Pr, Nd and Sm modified HZSM-5 zeolite catalysts for the catalytic decomposition of methyl mercaptan to a certain extent, of which the Sm modified HZSM-5 molecular sieves show the best reaction activity. On the one hand, the addition of rare earth Sm, HZSM The alkaline enhancement in -5 is beneficial to the adsorption and activation of acid methyl mercaptan molecules, thus improving the activity of the catalyst. On the other hand, the addition of rare earth Sm in HZSM-5 can partly replace the skeleton species in the zeolite molecular sieve, reducing the B acid content on the catalyst, reducing the number of strong acid active sites and reducing the number of the strong acid active sites. The production of less carbon has significantly increased the stability of catalytic catalytic decomposition of Methanthiol. The cause of deactivation and regeneration process of the rare earth modified HZSM-5 zeolite catalyst has been studied. The results show that the accumulation of carbon is the main cause of the deactivation of the zeolite catalyst for HZSM-5 zeolite, and the deactivated catalyst is at 550 centigrade. It can be easily regenerated many times in the gas.
【学位授予单位】：昆明理工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：X701;O647.3

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