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。在最终使用之前，许多氢必须经过清理反应。在燃料电池中广泛使用的一种这样的反应包括催化去除少量不需要的一氧化碳(CO)，该反应被称为一氧化碳优先氧化(CO-PREX)。这项研究将集中在水在CO Prox反应和其他相关催化反应中的重要作用。该项目将建立在研究人员以前研究的基础上，以更详细地了解水如何促进催化CO-prox，同时探索水或其他具有类似特性的分子可在多大程度上促进额外的工业反应，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的合作将为三一大学的本科生(其中许多人来自拉美裔背景)提供机会，与宾夕法尼亚州立大学的研究生合作开展研究。通过他们之前的联合研究项目，研究人员在激励他们的本科生继续接受化学和工程研究生课程方面取得了良好的成绩。在过去的30年里，CO氧化和CO-prox已经引起了相当大的科学和商业兴趣。尽管受到了这样的关注，但由于缺乏对反应机理的基本了解，开发PROX催化剂的进展一直受到阻碍。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氧化反应机理，解释了负载型催化剂、表面科学和计算文献中大多数不同的结果。这一新机理的主要特点是水作为弱酸碱助催化剂的作用。水首先作为质子供体，以Au-oh的形式促进O2与Au的结合。反应性的Au-OOH中间体将CO氧化成Au-COOH；然后水作为弱碱，在Au-COOH分解释放二氧化碳时接受质子。该项目将进一步确定Au-Oh中间体的特征，并扩大这一新的氧化化学的范围，在这种化学中，水起到“质子穿梭”的作用，在金属上来回运送质子。将使用各种光谱技术来识别和表征催化剂表面的Au-OH值作为水和氧气压力的函数。Au-OOH是一种潜在的强而选择性的氧化剂，为在新的氧化反应中使用Au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，将寻求一种名为“协同双功能催化”的新方法，在该方法中，金属粒子和弱酸碱化学将在活性中心协同工作。通过这种方法，将开发新的质子航天器来取代水作为金属氧化物表面的主要质子载体，从而允许在更高的温度下进行协同双功能催化。反应动力学和动力学同位素效应测量将证实在高温下Au-OOH的生成。这一新的化学也将扩展到炔氧化/水合反应。众所周知，炔可以吸附在Au上，这使其成为开发新反应化学的极佳测试反应。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.