Spectroscopic Elucidation of Cu and Fe Active Sites in Zeolites

爱德华一世教授斯坦福大学的所罗门正在利用化学系化学催化计划的资金，研究甲烷（和其他简单烃）在Cu和Fe交换沸石中Cu/O和Fe/O活性位点的选择性羟基化。甲烷（天然气中的主要成分）的羟基化产生可用作液体燃料的甲醇。事实上，甲烷是世界上最丰富的化石燃料，但也是一种强大的温室气体。 它直接转化为甲醇将是一种有价值的绿色能源，减少我们对石油储备的依赖，并减少一种温室气体。 该项目的重点是了解与沸石（一种多孔矿物）结合的Cu和Fe离子如何促进甲烷和其他简单烃的选择性氧化，以生产液体燃料和化学前体，用于工业上重要的反应。这些研究将有助于合理的催化剂设计，使更有效地利用烃原料。与该研究计划相结合的外联活动加强了当地高中教师的专业发展，并为当地高中学生提供了体验化学研究的机会。甲烷的选择性羟基化（和其他简单的烃）在铜和铁交换沸石正在研究使用耦合光谱和计算方法，以阐明几何形状，电子结构，以及Cu/O和Fe/O活性中心对烃反应性的贡献。 共振拉曼光谱表明，[Cu 2 O]2+物种是在Cu-ZSM-5的催化位点。目前的研究方向是：（1）利用各种位置选择性光谱方法进一步确定该活性中心;（2）了解N_2O和O_2生成[Cu_2O]~（2+）的机理;（3）确定CH_3OH生成的完整反应坐标、产物结合位点的性质及其过氧化机理; 4）评估其他沸石中的Cu/O2位点的结构/功能相关性和增强的反应性; 5）将这些研究扩展到Fe-ZSM-5和其他Fe沸石，以了解选择性氧化和产物结合的机制; 6）了解Fe-与Cu-ZSM-5的反应性差异;和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Cu和Fe的金属酶中的潜在类似位点相关，以建立生物催化和多相催化之间的对应关系。从这项研究中获得的分子水平的洞察力将为合理的催化剂设计提供信息，并使甲烷等烃原料的利用更加有效。特别是，将甲烷衍生的甲醇作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.