Understanding Structure-Function Relationships and Dynamical Restructuring in Near Surface Alloy Catalysts for Selective Oxidations

碳氢化合物的部分氧化可以产生含有氧原子的化合物（含氧化合物）。 含氧化合物是高价值的化学品，是工业过程中必不可少的中间体，也是许多消费品中的重要成分。部分氧化反应需要有效的催化剂，该催化剂选择性地产生所需的二氧化碳，而不将化合物完全氧化成二氧化碳。开发比目前化学制造中使用的催化剂更有效和选择性更高的催化剂对于降低制造成本，同时减少能源消耗和环境影响至关重要。改进的催化剂和催化工艺也将提高美国化学工业的竞争力和可持续性。该研究项目将研究一种新型催化剂，该催化剂由廉价的铜纳米颗粒上的单层银原子组成。 此类催化剂对于不饱和烃选择性部分氧化成环氧化物型含氧化合物具有显著的前景。研究人员将使用实验和计算方法来制备催化剂，评估其性能，并了解催化剂的结构和电子性质如何影响其反应性和选择性。从这项研究中获得的知识将为化学制造过程中下一代部分氧化催化剂的设计铺平道路。 该项目还包括一个推广计划，以当地的高中，研究生将协助高中学生准备他们的介绍，为当地的科学博览会。该项目的参与者还将与邻近的一所大学合作开展一项向上的数学科学项目，为低收入和第一代大学生提供早期研究经验。理论预测，近表面合金具有独特的电子结构，导致偏离限制传统催化剂的标度关系。然而，这样的催化剂表现出由在相关反应条件下发生的偏析和重构引入的固有无序和不均匀性。该研究项目旨在利用表面科学模型研究，密度泛函理论模拟和稳态催化动力学对AgCu近表面合金进行原子级理解。一个银封端的，AgCu近表面合金已被选择用于研究，由于其有前途的催化性能的部分氧化反应，这需要有效的活化分子氧和弱的表面结合的中间体。初步数据显示，这些近表面合金通过下面的铜对银层的电子改性来增强分子氧活化。 在反应条件下，孤立的铜原子被动态暴露，这进一步增加了分子氧活化速率，同时在表面保持大部分银位点。银位点通过双功能机制促进选择性氧化。初步的数据还包括动态重组AgCu近表面合金的表面氧化的证据。 这种重组产生高活性和选择性的模型催化表面，显示100%的选择性丁二烯环氧化。在这些初步数据的基础上，本研究项目将研究模型AgCu近表面合金的结构演变和环氧化反应，并使用密度泛函理论来增强对近表面合金的结构，能量学和电子特性的理解。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The partial oxidation of hydrocarbons can generate compounds that contain oxygen atoms (oxygenates). Oxygenates are high-value chemicals that are essential intermediates in industrial processes and important ingredients in many consumer products. Partial oxidation reactions require efficient catalysts that selectively yield the desired oxygenate without completely oxidizing the compound to carbon dioxide. The development of more efficient and selective catalysts than those used in current chemical manufacturing is essential for decreasing manufacturing costs while reducing energy consumption and environmental impacts. Improved catalysts and catalytic processes also will enhance the competitiveness and sustainability of the U.S. chemical industry. This research project will study a new class of catalysts comprised of a single layer of silver atoms on inexpensive copper nanoparticles. Such catalysts hold significant promise for the selective partial oxidation of unsaturated hydrocarbons to epoxide-type oxygenates. The researchers will use experimental and computational methods to prepare the catalysts, to evaluate their performance, and to understand how the structure and electronic properties of the catalyst influence its reactivity and selectivity. The knowledge gained from this research will pave the way for the design of a next generation of partial oxidation catalysts for chemical manufacturing processes. The project also includes an outreach program to a local high school in which graduate students will assist high-school students in preparing their presentations for a local science fair. The project participants also will collaborate with a neighboring university on an Upward Bound Math Science program to provide early research experiences to low-income and first-generation college bound students.Near-surface alloys have been predicted by theory to have unique electronic structures that lead to deviations from scaling relationships that limit traditional catalysts. However, such catalysts exhibit intrinsic disorder and inhomogeneity introduced by segregation and restructuring that occur under relevant reaction conditions. This research project aims to develop an atomic-level understanding of AgCu near-surface alloys using surface science model studies, density functional theory simulations, and steady-state catalysis kinetics. A silver -terminated, AgCu near-surface alloy has been chosen for study due to its promising catalytic properties for partial oxidation reactions, which require both efficient activation of molecular oxygen and weak surface binding of intermediates. Preliminary data shows that these near-surface alloys enhance molecular oxygen activation by electronic modification of the silver layer by the underlying copper. Under reaction conditions isolated copper atoms are dynamically exposed, which further increases the molecular oxygen activation rate while maintaining a majority of silver sites at the surface. The silver sites promote selective oxidation via a bifunctional mechanism. The preliminary data also includes evidence for dynamic restructuring of AgCu near-surface alloys in response to surface oxidation. This restructuring yields highly active and selective model catalytic surfaces displaying 100% selective butadiene epoxidation. Building on these preliminary data, this research project will study the structural evolution and epoxidation reactions on model AgCu near-surface alloys and use density functional theory to enhance understanding of the structure, energetics, and electronic properties of the near-surface alloys. New AgCu near-surface alloy epoxidation catalysts will be synthesized and tested.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.