Surface-level investigations of adsorbate-adsorbate interactions on thiolate-modified surfaces

设计催化剂中心以实现对所需产品的高选择性是当前多相催化研究的中心目标之一。这一目标在具有多个官能团的分子的反应中尤其具有挑战性，其中每个官能团都可以与催化表面相互作用并进行反应。一个很好的例子是将生物质转化为燃料和化学品。生物质衍生的碳水化合物和脂肪是含氧量很高的化合物，通常每个分子上都含有多个官能团(如醇、羧酸、酯、烯烃、醚、醛和酮)。选择性地驱动此类分子中单个官能团的特定反应的能力是重要的，特别是对于产生高价值的副产品来生产燃料。遗憾的是，在传统的负载型金属催化剂上实现如此高的选择性是非常复杂的，因为在许多催化剂中，所有的关键官能团都可以吸附在铂族金属上并进行反应。科罗拉多大学博尔德分校的J.William Medlin教授提出了一种不同的方法。他寻求设计具有高选择性的新型催化剂，同时考虑到生物催化剂(酶)。酶催化剂利用结合口袋中的非共价相互作用来控制化学转化，从而产生无与伦比的选择性，即使与多功能反应物分子也是如此。因此，提高金属表面选择性的一种方法是创造一个近表面环境(NSE)，模拟酶口袋，促进试剂与表面的选择性相互作用。这些NSE可以通过将有机配体附着到表面上来生成。在其他研究中，这一概念的变体已被用于在铂基表面产生手性结合口袋。这些修饰催化表面的努力试图利用反应物和孤立的共价连接的表面配体之间的相互作用。PI建议使用组织良好的分子表面层来创建均匀和/或分层的NSE，很像生物膜中的NSE。Medlin已经用高选择性钯催化剂证明了这一概念，包括沉积正硫醇自组装单分子层(SAM)涂层，大大提高了1-环氧-3-丁烯加氢生成1-环氧丁烷的选择性(11%至94%)。梅德林的建议扩展了对NSE中吸附物和其他分子之间的相互作用如何改变金属表面反应性的研究，假设通过控制吸附物和NSE之间的相互作用，有可能控制重要试剂的吸附几何形状和随后的反应性。为了控制NSE，将使用从丰富的分子和化学成分目录中选择的有机硫醇自组装膜在金属表面沉积。许多可能的演示反应将被考虑来评估效果。进行这项研究的博士生将受益于拟议的国际研究部分，包括位于苏黎世的瑞士联邦理工学院的束流时间。本科生将在博士生研究的基础上进行小规模项目的独立研究。外展活动将通过Medlin积极参与的现有项目来组织，包括由可再生能源材料研究科学与工程中心、科罗拉多州生物精炼和生物燃料中心以及可再生和可持续能源研究所推动的项目。

The objective of designing catalyst sites to achieve high selectivity to desired products is one of the central goals of current research in heterogeneous catalysis. This objective can be particularly challenging in reactions of molecules which possess multiple functional groups, and where each functional group can interact with the catalytic surface and undergo reaction. A good example is the conversion of biomass to fuels and chemicals. Biomass-derived carbohydrates and lipids are highly oxygenated compounds that generally contain multiple functional groups (e.g., alcohols, carboxylic acids, esters, olefins, ethers, aldehydes, and ketones) on each molecule. The ability to selectively drive a specific reaction of a single functional group in such molecules is important, particularly for generating high value coproducts to fuels. Unfortunately, achieving this high selectivity on conventional supported metal catalysts is greatly complicated, as all of the key functional groups can adsorb and react on the Pt-group metals in many catalysts. Professor J. William Medlin at the University of Colorado at Boulder proposes a different approach. He seeks to design novel catalysts for high selectivity with biological catalysts (enzymes) in mind. Enzyme catalysts exploit non-covalent interactions within binding pockets to control chemical transformations, resulting in unsurpassed selectivity, even with multifunctional reactant molecules. One approach therefore for improving the selectivity of metal surfaces is to create a near-surface environment (NSE) that fosters selective interactions of reagents with surfaces, mimicing an enzyme pocket. These NSEs can be created through attachment of organic ligands to the surface. Variations on this concept have been used in generating chiral binding pockets on Pt-group surfaces in other research. These efforts to modify catalytic surfaces sought to exploit interaction between reactants and isolated covalently-attached surface ligands. The PI proposes to use well-organized molecular surface layers to create uniform and/or stratified NSEs, much like in biomembranes. Medlin has proven the concept with highly selective Pd catalysts involving the deposition of n-alkanethiol self-assembled monolayer (SAM) coatings with dramatic improvement of the selectivity (11 to 94%) of 1-epoxybutane formation from hydrogenation of 1-epoxy-3-butene. Medlin's proposal extends the investigation of how interactions between adsorbates and other molecules in the NSE alter the reactivity of metal surfaces, with the hypothesis being that by controlling interactions between adsorbates and the NSE, it is possible to control the adsorption geometry and subsequent reactivity of important reagents. To control the NSE, deposition on metal surfaces of organic thiol SAMs selected from a rich catalog of molecules and chemistries will be employed. Many possible demonstration reactions will be considered to evaluate the effects.The PhD student conducting the research will benefit from a proposed international research component including beam time at the Swiss Federal Institute of Technology in Zurich. Undergraduate students will conduct independent research on small-scale projects that build on the research of PhD student. Outreach activities will be organized through existing programs in which Medlin is active, including those promoted by the Renewable Energy Materials Research Science and Engineering Center, the Colorado Center for Biorefining and Biofuels, and the Renewable and Sustainable Energy Institute.