RUI:Collaborative Research: Understanding and exploiting proton mobility in Au catalyzed selective oxidation reactions

美国每年生产超过 90 亿吨氢气 (H2)。 大部分氢气在最终使用前必须进行净化反应。 广泛用于燃料电池的此类反应涉及在称为一氧化碳优先氧化（CO-PROX）的反应中催化去除少量不需要的一氧化碳（CO）。 该研究将重点关注水在 CO PROX 反应和其他相关催化反应中的重要作用。 该项目将以研究人员之前的研究为基础，更详细地了解水如何促进催化 CO-PROX，同时探索水或具有类似特征的其他分子在多大程度上可用于促进其他工业反应，例如涉及碳氢化合物的反应。 三一大学（一所小型本科院校）与宾夕法尼亚州立大学之间的合作将为三一大学的本科生（其中许多来自西班牙裔背景）提供与宾夕法尼亚州立大学的研究生合作进行研究的机会。 通过之前的联合研究项目，研究人员在激励本科生继续化学和工程研究生课程的教育方面取得了良好的记录。过去 30 年来，CO 氧化和 CO-PROX 引起了相当大的科学和商业兴趣。 尽管受到如此关注，但由于缺乏对工作反应机制的基本了解，PROX 催化剂的开发进展受到阻碍。 基于实验观察和密度泛函理论（DFT）计算，研究人员最近提出了一种新的CO氧化反应机制，可以解释负载型催化剂、表面科学和计算文献中的大多数不同结果。这种新机制的关键特征是水作为弱酸碱助催化剂的作用。水首先充当质子供体，促进 O2 以 Au-OOH 形式与 Au 结合。反应性Au-OOH中间体将CO氧化成Au-COOH；然后水充当弱碱，在 Au-COOH 分解并释放 CO2 时接受质子。 该项目将进一步表征 Au-OOH 中间体，并扩大这种新型氧化化学的范围，其中水充当“质子穿梭机”，将质子往返于金属上的反应性中间体。 将采用各种光谱技术来识别和表征催化剂表面上的 Au-OOH 作为水和氧压力的函数。 Au-OOH 是一种潜在的强选择性氧化剂，为在新的氧化反应中使用金催化剂提供了机会。然而，它依赖于与弱吸附水相关的弱酸碱化学，这限制了获得 Au-OOH 的反应条件。为此，将寻求一种称为“协同双功能催化”的新方法，其中金属颗粒和弱酸/碱化学将在活性位点协同工作。 通过这种方法，将开发新的质子穿梭机来取代水作为金属氧化物表面上的主要质子载体，从而允许在更高的温度下发生协同双功能催化。 高温下 Au-OOH 的生成将通过反应动力学和动力学同位素效应测量来证实。这种新颖的化学反应也将扩展到炔烃氧化/水合反应。众所周知，炔烃会吸附在金上，这使其成为开发新反应化学物质的绝佳测试反应。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。

The US produces more than nine billion tons of hydrogen (H2) gas per year. Much of the hydrogen must undergo clean-up reactions prior to end use. One such reaction used widely for fuel cells involves catalytic removal of small amounts of unwanted carbon monoxide (CO) in a reaction known as preferential oxidation of carbon monoxide (CO-PROX). The study will focus on the important role of water in the CO PROX reaction and other related catalytic reactions. This project will build on previous studies by the investigators to provide more detailed understanding of how water promotes catalytic CO-PROX while exploring the extent to which water, or other molecules with similar characteristics, can be used to promote additional industrial reactions such as those involving hydrocarbons. The collaboration between Trinity University - a small undergraduate institution - and Pennsylvania State University will provide opportunities for undergraduates from Trinity (many of whom come from Hispanic background) to conduct research in collaboration with graduate students from Penn States. Via their previous joint research projects, the investigators have developed an excellent track record of inspiring their undergraduate students to continue their education in both chemistry and engineering graduate programs. CO oxidation and CO-PROX have been of considerable scientific and commercial interest for the past 30 years. Despite this attention, progress in developing PROX catalysts has been hindered by lack of fundamental understanding of the reaction mechanisms at work. Based on experimental observations and density functional theory (DFT) calculations, the investigators have recently proposed a new CO oxidation reaction mechanism that explains most of the disparate results in the supported catalyst, surface science, and computational literature. The key feature of this new mechanism is the role of water as a weak acid-base co-catalyst. Water first acts as a proton donor, facilitating O2 binding to Au as Au-OOH. The reactive Au-OOH intermediate oxidizes CO to Au-COOH; water then acts as a weak base, accepting a proton as Au-COOH decomposes to release CO2. This project will further characterize the Au-OOH intermediate and expand the scope of this new oxidation chemistry, in which water acts as a "proton shuttle", carrying protons to and from reactive intermediates on the metal. A variety of spectroscopic techniques will be employed to identify and characterize Au-OOH on the catalyst surface as a function of water and oxygen pressures. Au-OOH is a potentially strong yet selective oxidant, offering opportunities to use Au catalysts in new oxidation reactions. However, it relies on the weak acid-base chemistry associated with weakly adsorbed water, which limits the reaction conditions under which Au-OOH is accessible. To this end, a new approach termed "collaborative bifunctional catalysis" will be pursued in which the metal particle and weak acid/base chemistry will work in concert at the active site. Via this approach, new proton shuttles will be developed to replace water as the primary proton carrier on metal oxide surfaces, thus allowing for collaborative bifunctional catalysis to take place at higher temperatures. Generation of Au-OOH at elevated temperatures will be confirmed by reaction kinetics and kinetic isotope effect measurements. The novel chemistry will also be extended to alkyne oxidation/hydration reactions. Alkynes are well known to adsorb onto Au, making this an excellent test reaction to develop new reaction chemistries.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.