Mechanism of Epoxidation of Propylene with H2/O2 Mixtures

项目编号：0651238首席研究员：Oyama， S. ted机构：Virginia Polytechnic Institute and State UniversityScientific Merit。丙烯与气相氢和氧混合物的环氧化反应是相当重要的，可能取代目前使用过氧化氢或有机过氧化物的工艺。虽然该反应具有商业意义，但其作用机理尚未阐明，对其更深入的了解将有助于改进催化剂。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，然后迁移到钛中心形成氢过氧化物，这是导致环氧化反应的原因。我们计划使用多种原位技术，包括紫外-可见（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）来研究该催化体系，以研究工作催化剂的结构和功能，从而深入了解其运作机制。这些研究将由从头计算Hartree-Fock计算来描述活性位点和吸附物。在反应条件下使用紫外-可见和LRS对催化剂进行研究，将提供过氧化氢吸附中间体和速率决定步骤（rds）性质的信息。FTIR将探测吸附有机部分的性质。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，而原位XANES将用于探测反应条件下金的氧化态。报道的最佳催化剂是负载在微孔沸石TS-1上的金。研究人员将通过使用TS-1构建块创建介孔结构来改进催化剂。介孔可以使反应物更好地进入活性位点，而微孔可以通过吸附反应产物来保护活性位点不失活。将通过改变沉积的pH值来研究金粒度的影响。催化剂还将在膜反应器中进行研究，以确保氢和氧组分的安全混合。这些反应物的单独进料将允许在爆炸范围内使用浓度，而没有爆炸的危险。更高水平的氢和氧会导致更高的速率。更广泛的影响。拟议的项目对社会有广泛的好处。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，以研究催化剂的工作状态。其次，该项目具有很强的国际成分，因为研究的一部分将涉及使用日本国家研究所（先进工业科学技术研究所）的设施。学院已经批准了PI和学生的生活费。第三，该项目将重点培训和教育少数民族和妇女学生。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了成员，这将继续下去。第四，将与当地一所本科学校（雷德福大学）的一名教员开展实质性合作，以促进个人成长，并刺激该校学生参与高等教育。

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.