Mechanism of Epoxidation of Propylene with H2/O2 Mixtures

提案编号：0651238主要制造商：Oyama，S. TedInstitution：Virginia Polytechnic Institute and State University.丙烯与气相氢气和氧气混合物的环氧化反应作为使用过氧化氢或有机过氧化物的现有方法的可能替代物是相当重要的。虽然该反应具有商业意义，但其运行机制尚未阐明，更深入的了解将导致改进催化剂。现有的催化剂由分散在钛硅酸盐载体上的纳米级金颗粒组成。氧和氢的氧化剂混合物被认为在金颗粒上形成过氧化氢，其然后迁移到钛中心以形成氢过氧化物，其负责环氧化反应。我们计划使用几种原位技术，包括紫外-可见光（UV-vis）吸收光谱，激光拉曼光谱（LRS），傅里叶变换红外光谱（FTIR），和扩展和近边X射线吸收光谱（EXAFS，XANES）来研究工作催化剂的结构和功能，以获得洞察它们的运作机制。这些研究将得到从头算Hartree-Fock计算的支持，以描述活性位点和吸附物。在反应条件下使用原位UV-vis和LRS的催化剂的研究将提供有关氢过氧化物吸附的中间体和速率决定步骤（rds）的性质的信息。FTIR将探测吸附的有机部分的性质。将使用瞬态技术研究吸附的中间体，以确定它们是否以与反应的总体速率一致的速率对扰动作出反应，从而确定它们是反应性参与者还是仅仅是旁观者。原位EXAFS将用于研究钛中心的配位，原位XANES将探测反应条件下金的氧化态。报道最好的催化剂是载于微孔沸石TS-1上的金。将开展工作，以改善催化剂，创造与TS-1积木介孔结构。中孔性将使反应物更好地接近活性位点，而微孔性将保护活性位点免于因反应产物的吸附而失活。将通过改变沉积的pH来研究金的颗粒尺寸的影响。还将在膜反应器中研究催化剂，以使氢和氧组分安全混合。这些反应物的单独进料将允许使用爆炸范围内的浓度，而没有爆炸的危险。氢和氧的含量越高，反应速率就越高。拟议的项目具有广泛的社会效益。首先，这项研究不仅将促进对环氧化反应的理解，而且还将开发用于其他系统的通用技术，以研究处于工作状态的催化剂。第二，该项目具有很强的国际组成部分，因为研究的一部分将涉及使用日本国家研究所的设施（先进工业科学和技术）。PI和学生的生活费资金已经得到研究所的批准。第三，该项目将强调少数民族和妇女学生的培训和教育。在过去，我们的实验室已经成功地从代表性不足的群体中招募成员，这将继续下去。第四，将与当地一所本科学校（拉德福大学）的一名教员开展实质性合作。促进个人的个人成长，并鼓励该校学生参加高等教育。

PROPOSAL NUMBER: 0651238PRINCIPAL INVESTIGATOR: Oyama, S. TedINSTITUTION: Virginia Polytechnic Institute and State UniversityScientific Merit. The epoxidation reaction of propylene with gas-phase hydrogen and oxygen mixtures is of considerable importance as a possible replacement for current processes employing hydrogen peroxide or organic peroxides. Although the reaction is of commercial significance, the mechanism by which it operates has not been clarified, and a deeper understanding will lead to improved catalysts. Existing catalysts consists of nano-sized gold particles dispersed on a titanosilicate support. The oxidant mixture of oxygen and hydrogen is believed to form hydrogen peroxide on the gold particles, which then migrates to titanium centers to form hydroperoxides, which are responsible for the epoxidation reaction. We plan to study this catalytic system using several in situ techniques, including ultraviolet-visible (UV-vis) absorption spectroscopy, laser Raman spectroscopy (LRS), Fourier transform infrared spectroscopy (FTIR), and extended and near-edge x-ray absorption spectroscopy (EXAFS, XANES) to study the structure and function of working catalysts so as to obtain insight on the mechanism by which they operate. The studies will be supported by ab initio Hartree-Fock calculations to describe active sites and adsorbates. Study of the catalysts at reaction conditions using in situ UV-vis and LRS will give information about the hydroperoxide adsorbed intermediate and the nature of the ratedetermining step (rds). FTIR will probe the nature of adsorbed organic moieties. The adsorbed intermediates will be studied using transient techniques to determine whether they respond to perturbations at a rate consistent with the overall rate of reaction, and thus, to establish whether they are reactive participants or merely spectators. In situ EXAFS will be used to study the coordination of the Ti centers, and in situ XANES will probe the oxidation state of the gold at reaction conditions. The best reported catalyst is gold supported on the microporous zeolite TS-1. Work will be carried out to improve the catalyst by creating mesoporous structures with TS-1 building blocks. The mesoporosity will give the reactants better access to the active sites, while the microporosity will protect the sites from deactivation by adsorption of products of reaction. The effect of the particle size of the gold will be studied by varying the pH of deposition. The catalysts will also be studied in a membrane reactor to allow the safe mixing of the hydrogen and oxygen components. The separate feed of these reactants will allow the use of concentrations within the explosive regime, without the danger of detonation. The higher levels of hydrogen and oxygen should lead to higher rates.Broader Impact. The proposed project has broad aspects of benefit to society. First, the research will not only advance understanding of the epoxidation reaction, but will also develop general techniques for use in other systems to study catalysts in their working state. Second, the project has a strong international component, as part of the research will involve use of facilities at a National Institute in Japan (Advanced Industrial Science and Technology-AIST). Funds for living costs for the PI and students have already been approved from the Institute. Third, the project will have an emphasis in the training and education of minority and women students. In the past our laboratory has successfully recruited members from underrepresented groups and this will be continued. Fourth, a substantive collaboration will be initiated with a faculty member from a local undergraduate school (Radford Univ.) to promote personal growth of the individual, as well as to stimulate the participation of students from that school in higher education.