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Characterizing Bond Activation in Alkanes and Alkyl Halides by Metal and Metal Cluster Cations using Spectroscopy and Photofragment Imaging

使用光谱学和光碎片成像表征金属和金属簇阳离子在烷烃和烷基卤化物中的键活化

基本信息

批准号：
1856490
负责人：
Ricardo Metz
金额：
$ 50万
依托单位：
University of Massachusetts Amherst
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2019
资助国家：
美国
起止时间：
2019-07-01 至 2022-06-30
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1856490&HistoricalAwards=false
关键词：
Characterizing Bond Activation Alkanes Alkyl

项目摘要

In this project, funded by the Chemical Structure, Dynamics, and Mechanisms-A program of the Chemistry Division, Professor Ricardo Metz and his students at the University of Massachusetts Amherst are studying how alkanes and alkyl halides can be converted to more industrially useful chemicals. Although natural gas is mostly methane (CH4), it also has up to 6% ethane and 4% propane. Ethane and propane are extremely useful, as they can be converted into ethylene and propylene, which are then used to produce plastics like polyethylene and polypropylene, or other higher value chemicals. Industrially, the production of ethylene and propylene require a great deal of energy and they produce over a pound of carbon dioxide for every pound of ethylene produced. The Metz group uses specialized instruments in which streams of molecules under high vacuum interact with laser light to produce products like ethylene or propylene. Both graduate and undergraduate students are involved in this research project. In addition to gaining and disseminating knowledge about the chemistry of molecular systems, the students are receiving training in advanced laser techniques and vacuum technologies, as well as computational chemistry, which is used to help interpret the experimental results. Professor Metz is also helping to introduce eighth-grade girls to research in STEM fields through the Eureka! program.Complexes of metal ions and metal cluster ions with ethane and propane are produced in a laser ablation/flow reactor source, cooled via supersonic expansion, mass selected in a mass spectrometer and their structure and bonding is characterized using vibrational and electronic spectroscopy. Interaction with the metal weakens the carbon-hydrogen (C-H bonds) in the ethane or propane ligand; this weakening is key to the subsequent catalytic activation of the bond. The experiments measure the extent of C-H bond weakening and polarization by the metal, as they lead to lower frequencies for the corresponding C-H stretch vibrations. These experiments also reveal the identity of reaction intermediates and products in cases where several isomers could be involved, as in competitive C-H and C-C bond insertion. These studies are being carried out for several metals and for clusters with differing numbers of metal atoms to determine the electronic and structural factors that lead to size-dependent reactivity. Complementary velocity map imaging studies of metal halide, sulfide and carbene cation photodissociation measure kinetic energy release and fragment anisotropy, determining accurate bond strengths and probing the couplings between excited electronic states. Photodissociation of a metal halide are also being used to initiate a bimolecular reaction between a metal cation and an alkane, allowing the team to study reaction dynamics with controlled impact parameter and orientation, as a function of translational energy. The broader impacts of this work include potential benefits from improved catalysts as well as training undergraduate and graduate students in mass spectrometry and laser spectroscopy and in broader skills such as problem solving, experimental design, data acquisition and analysis and communication of their results.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

在这个由化学部化学结构、动力学和机理项目资助的项目中，里卡多·梅茨教授和他在马萨诸塞大学阿默斯特分校的学生正在研究如何将烷烃和烷基卤转化为工业上更有用的化学品。虽然天然气主要成分是甲烷 (CH4)，但也含有高达 6% 的乙烷和 4% 的丙烷。乙烷和丙烷非常有用，因为它们可以转化为乙烯和丙烯，然后用于生产聚乙烯和聚丙烯等塑料或其他更高价值的化学品。在工业上，乙烯和丙烯的生产需要大量能源，每生产一磅乙烯就会产生超过一磅的二氧化碳。梅斯小组使用专门的仪器，使高真空下的分子流与激光相互作用，产生乙烯或丙烯等产品。研究生和本科生都参与了这个研究项目。除了获得和传播有关分子系统化学的知识外，学生们还接受先进激光技术和真空技术以及计算化学的培训，用于帮助解释实验结果。梅茨教授还通过“尤里卡！”帮助向八年级女孩介绍 STEM 领域的研究！程序。金属离子和金属簇离子与乙烷和丙烷的复合物在激光烧蚀/流动反应器源中产生，通过超音速膨胀冷却，在质谱仪中选择质量，并使用振动和电子光谱表征它们的结构和键合。与金属的相互作用削弱了乙烷或丙烷配体中的碳-氢（C-H键）；这种弱化是随后催化活化键的关键。实验测量了金属 C-H 键弱化和极化的程度，因为它们导致相应的 C-H 伸缩振动的频率较低。这些实验还揭示了可能涉及多种异构体的情况下反应中间体和产物的身份，例如竞争性 C-H 和 C-C 键插入。这些研究正在针对几种金属和具有不同金属原子数量的簇进行，以确定导致尺寸依赖性反应性的电子和结构因素。金属卤化物、硫化物和卡宾阳离子光解的互补速度图成像研究测量动能释放和碎片各向异性，确定准确的键强度并探测激发电子态之间的耦合。金属卤化物的光解离也被用来引发金属阳离子和烷烃之间的双分子反应，使团队能够研究具有受控冲击参数和方向的反应动力学，作为平移能量的函数。这项工作的更广泛影响包括改进催化剂的潜在好处，以及对本科生和研究生进行质谱和激光光谱方面的培训，以及对问题解决、实验设计、数据采集和分析以及结果交流等更广泛技能的培训。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。