【作者】 姚林；

【导师】 张宁； 陈超；

【作者基本信息】 南昌大学 ， 工业催化， 2008， 硕士

【摘要】 甲基丙烯酸甲酯（MMA）是重要的丙烯酸树脂单体,市场应用前景十分广阔。MMA传统的合成方法是以丙酮、剧毒的氢氰酸和硫酸为原料,不仅是非环境友好工艺,且副产大量硫酸氢铵。因此,异丁烯选择氧化制备甲基丙烯醛（MAL）是作为异丁烯氧化法制备MMA清洁工艺的关键步骤得到人们的广泛关注,对该催化反应的催化剂及其反应规律进行研究具有重要的理论和实际意义。本文合成了V_x-UVM-7及用钼（Mo）改性后的系列催化剂,并用于异丁烯选择催化氧化研究。并以近年发展起来的研究催化剂表面反应作用机理的实验技术—原位漫反射红外光谱技术对此催化体系进行了机理探索,具体实验内容如下:从异丁烯氧化原理出发,在以具有高比表面及比孔容的双峰介孔材料UVM-7的基础上用钒（V）原子取代结构中的硅（Si）,探讨通过V杂原子取代制备而成V_x-UVM-7系列催化剂及用Mo进行改性以后在异丁烯氧化制取甲基丙烯醛反应中的催化性能。用杂氮三环络合物法（atrane法）制备了V_x-UVM-7介孔分子筛催化剂和用Mo、V同时取代Si元素之后的Mo-V-UVM-7催化剂。催化剂的评选在固定床反应器中进行,考察了反应温度、异丁烯浓度、原料气的流速、含V量的不同及同等含钒量情况下Mo不同掺杂方式对异丁烯转化率和生成MAL选择性的影响。筛选出活性及选择性较高的催化剂,并用XRD、FT-IR、SEM、ICP、N₂吸附-脱附、UV-vis、TG等表征技术对催化剂进行了表征。实验结果表明,在最佳工艺条件下,异丁烯转化率和MAL的选择性分别可达82.6%、35.6%。在确定自建的原位漫反射红外实验装置的分辨率、扫描次数、催化剂粒径和气速等参数的较佳操作值的基础上动态考察了异丁烯氧化的催化剂表面反应和气相反应行为。探索了异丁烯氧化制取甲基丙烯醛的反应机理,为改进催化剂提供了理论依据。结果表明:催化剂表面的选择氧化能够有效抑制深度产物CO₂,CO的生成量,选择氧化的活性中心是催化剂表面的晶格氧。催化剂表面的异丁烯氧化反应有多种反应路径,实验中检测到的中间产物主要有:（ⅰ）p-allylic络合物;（ⅱ）异丁烯与催化剂表面的Br（o|¨）nsted酸位作用形成的甲基烯丙醇物种;（ⅲ）叔丁醇中间物种。更多还原

【Abstract】 Methyl methacrylate （MMA） is an important precursor in the preparation of acrylic resins. Acetone, highly toxic hydrocyanic acid and sulphuric acid are used as raw materials in traditional method to produce MMA. The seriously poisonous substances and the strong acid not only results in the obvious environment pollution, but also results in the numerous ammonium bisulfate byproduct. Therefore, the selective oxidation of isobutene to methacrolein （MAL） which is a critical step for clean production of MMA from isobutene has been extensively studied for a long time worldwide. So the studies on catalysts and catalytic reaction process for selective oxidation of isobutene to methacrolein are important for both fundamental understanding and industrial application. In the paper, we synthesized series catalysts of V_x-UVM-7 and the V-UVM-7 modified with molybdenum （Mo） element and tested for the oxidation of isobutene. Then, we used in-situ DRIFTS technique to probe the mechanism of selective oxidation of isobutene. The technique is always applied to study surface reaction mechanism recently. Specific experiments as follows:Based on the main existing mechanism of selective oxidation of isobutene, we substituted the silicon （Si） with vanadium （V） in the bimodal mesoporous molecular sieve UVM-7 which possesse high specific surface and specific pore volume and explored the catalytical performance of the mesoporous system V_x-UVM-7 and the V-UVM-7 modified with molybdenum （Mo） element in the oxidation of isobutene to MAL. We have prepared V_x-UVM-7 series catalysts and Mo-V-UVM-7 catalysts in which the Mo element also substituted Si element or supported on the mesoporous materials with atrane route method and impregnation method. The oxidizing reactions were carried out in the fixed bed reactor. Simultaneously, we have studied some factors which can influence the conversion of isobutene and the selectivity of the methacrolein. These factors include the temperature of the reaction, the concentration of the isobutene, the flowing rate of raw material gas, the different content of V element and the different methods of incorporating Mo element into the mesoporous materials. We have synthesized many kinds of new catalysts and selected some of them with higher activity and selectivity. Furthermore, we have characterized these catalysts by means of XRD, FT-IR, TEM, ICP, N₂ adsorption/desorption, UV-vis and TG technologies. Results indicated that under the optimal reaction conditions, conversion of isobutene and selectivity of MAL reaches 82.6% and 35.6%, respectively.Some parameters such as the resolution, scanning time, catalyst particle size and gas velocity are fixed at best values of self-building in-situ DRIFTS experimental installation, and then it is systemically investigated for the isobutene selective oxidation over Mo-V-UVM-7 catalyst, including surface reaction and gas reaction behavior. Then the catalytic reaction mechanism, which can provide theoretical foundation for improving the catalyst, were discussed with the results of in-situ DRIFTS experiment. The selective oxidation of isobutene over catalyst surface effectively controls deep oxidation products of isobutene such as carbon dioxide and carbon monoxide. The centers of active sites of selective oxidation are surface lattice oxygens. The nature of adsorbed intermediates detected by in-situ DRIFTS are: （ i） a p-allylic intermediate; （ii） an enolic type compound formed in the presence of Bronsted acid sites; （iii） a p-bonedisobutene species interacting with Lewis acid site.更多还原