Spectroscopic Elucidation of Cu and Fe Active Sites in Zeolites

斯坦福大学的爱德华·I·所罗门教授正在利用化学系化学催化计划的资金，研究甲烷(和其他简单碳氢化合物)在铜和铁交换沸石的铜/O和铁/O活性中心的选择性羟化反应。甲烷(天然气中的主要成分)的羟基化反应产生可用作液体燃料的甲醇。事实上，甲烷是世界上储量最丰富的化石燃料，但也是一种强有力的温室气体。它直接转化为甲醇将是一种宝贵的绿色能源，减少我们对石油储量的依赖，并减少其中一种温室气体。这个项目的重点是了解结合到沸石(一类多孔矿物)上的铜和铁离子如何促进甲烷和其他简单碳氢化合物的选择性氧化，以产生液体燃料和工业上重要反应的化学前体。这些研究将有助于合理的催化剂设计，从而能够更有效地利用碳氢化合物原料。与这项研究计划相结合的外展活动促进了当地高中教师的专业发展，并为当地高中生提供了体验化学研究的机会。目前正在使用耦合光谱和计算方法研究铜和铁交换沸石中甲烷(和其他简单碳氢化合物)的选择性羟化反应，以阐明铜/氧和铁/氧活性中心的几何结构、电子结构和对碳氢化合物反应的贡献。共振拉曼光谱表明，[Cu2O]2物种是Cu-ZSM-5的催化中心。现在的研究方向是：1)使用各种位置选择光谱方法来进一步确定该活性中心；2)了解N2O和O2形成[Cu2O]2的机理；3)确定CH3OH形成的完整反应坐标、产物结合位置的性质及其过氧化机理；4)评估其他沸石中的铜/O2中心的结构/功能相关性和增强的反应活性；5)将这些研究扩展到Fe-ZSM-5和其他Fe分子筛，以了解选择性氧化和产物结合的机理；6)了解Fe-ZSM-5和Cu-ZSM-5的反应活性差异；以及7)将这些研究扩展到其他TMI/沸石/O2反应和中间体。这些研究与含铜和铁的金属酶中潜在的类似位置相关，以建立生物催化和多相催化之间的对应关系。这项研究从分子水平上得出的见解将为合理的催化剂设计提供信息，并使甲烷等碳氢化合物原料能够更有效地使用。特别是，将甲烷衍生的甲醇确立为一种可行的绿色能源将保护环境，减少我们对石油储备的依赖。

Professor Edward I. Solomon of Stanford University is using funds from the Chemical Catalysis program of the Chemistry Division to study the selective hydroxylation of methane (and other simple hydrocarbons) at Cu/O and Fe/O active sites in Cu- and Fe-exchanged zeolites. The hydroxylation of methane (the chief component in natural gas) produces methyl alcohol that can be used as a liquid fuel. In fact, methane is the world's most abundant fossil fuel, but is a potent greenhouse gas. Its direct conversion to methanol would be a valuable source of green energy, decrease our dependence on oil reserves, and reduce one of the greenhouse gasses. This project is focused on understanding how Cu and Fe ions bound to zeolites (a family of porous minerals) facilitate the selective oxidation of methane and other simple hydrocarbons to produce liquid fuels and chemical precursors for industrially significant reactions. These studies will aid in rational catalyst design, enabling more efficient use of hydrocarbon feedstocks. Outreach activities coupled to this research program enhance professional development of local high school teachers and provide local high school students the opportunity to experience chemical research.The selective hydroxylation of methane (and other simple hydrocarbons) in Cu- and Fe-exchanged zeolites is being investigated using coupled spectroscopic and computational methods to elucidate the geometries, electronic structures, and contributions to hydrocarbon reactivity of the Cu/O and Fe/O active sites. Resonance Raman spectroscopy indicates a [Cu2O]2+ species to be the catalytic site in Cu-ZSM-5. Studies are now directed toward: 1) using a variety of site selective spectroscopic methods to further define this active site; 2) understanding the mechanisms of formation of [Cu2O]2+ from N2O and O2; 3) defining the complete reaction coordinate for CH3OH formation, the nature of the product binding site, and the mechanism of its over oxidation; 4) evaluating the Cu/O2 sites in other zeolites for structure/function correlations and enhanced reactivity; 5) extending these studies to Fe-ZSM-5 and other Fe zeolites to understand the mechanisms for selective oxidation and product binding; 6) understanding differences in the reactivity of Fe- vs. Cu-ZSM-5; and 7) extending these studies to other TMI/zeolite/O2 reactions and intermediates These studies are correlated to potentially analogous sites in Cu- and Fe-containing metalloenzymes to establish correspondence between biological and heterogeneous catalysis. Molecular-level insight derived from this research will inform rational catalyst design and enable more efficient use of hydrocarbon feedstocks such as methane. In particular, establishing methanol derived from methane as a viable source of green energy would protect the environment and decrease our dependence on oil reserves.