Water-Assisted Oxygen Insertion Reactions Over Supported Gold Catalysts

由于页岩气生产的最新进展，天然气开采量的增加以及天然气价格的降低，美国拥有丰富的廉价天然气。甲烷是天然气的主要成分，已被广泛用作发电燃料;然而，它不是生产化学品或运输燃料（如汽油或柴油）的良好原料。这是由于难以通过将氧原子插入到强的碳-氢键中来选择性地氧化甲烷，同时防止完全燃烧成二氧化碳和水。 众所周知，金在暴露于氧气或空气中时是惰性的，但当它被分成小的纳米颗粒时，它开始催化一氧化碳的氧化。 休斯顿大学的Grabow博士和Trinity大学的钱德勒博士最近发现了一种机制，即在氧化钛上负载的金纳米颗粒上，水在CO氧化过程中充当助催化剂。他们现在正在将这些知识转化为甲烷和其他烷烃的部分氧化，以形成相应的醇。该团队遵循一种合作和紧密耦合的方法，使用计算和实验研究来量化水对选择性氧化的促进作用，并研究氧插入碳氢键的主要反应机制。由于已确认的天然气储量超过7.72万亿立方米，因此有巨大的动力开发商业上可行的甲烷转化工艺，以造福美国经济并实现国家能源独立。研究活动与K-12、本科生、研究生和专业一级的广泛教育努力相结合，以扩大少数民族学生的参与，并提高两所参与大学中有风险学生的保留率。休斯顿大学是一所指定的西班牙裔服务机构，拥有美国所有主要研究机构中种族最平衡的学生群体Trinity University为圣安东尼奥和南德克萨斯州地区提供研究型本科教育，这些地区主要由STEM学科中传统上代表性不足的群体组成。休斯顿大学的Lars Grabow博士和Trinity大学的Bert钱德勒博士由NSF的化学催化计划资助，研究在支持的金催化剂上将氧插入碳氢键（C-H）的反应。 最终目标是选择性地将甲烷转化为甲醇，解决该问题的合理方法需要理论（Grabow）和实验（钱德勒）技术的紧密结合。在所有使用甲烷作为原料的工艺中，普遍存在的挑战是激活强C-H键;因此，最初的重点是具有较弱C-H键的高级烷烃，以获得有关氧（O）插入机制的相关知识。 为了实现使用少量水来提高负载型金（Au）催化剂氧化反应的活性和选择性的可能性，该团队量化了不同载体上的表面水量，研究了氧插入C-H键的主要反应机制，并在计算预测的指导下提高了产物产率。 选择的应用，O插入烷烃的C-H键，是化学中具有挑战性的基本问题，对天然气的升级具有深远的技术影响，有利于美国经济和实现国家能源独立。这一概念也可以推广到其他困难的选择性氧化反应，如乙烯环氧化反应。研究活动与K-12、本科生、研究生和专业一级的广泛教育努力相结合，以扩大少数民族学生的参与，并增加两所参与大学中有风险学生的保留率。总的来说，主要研究人员在指导本科生、少数民族和女学生的研究项目方面有着良好的记录。

Due to recent advances in shale gas production, increased natural gas recovery, and reduced natural gas prices, the United States has an abundance of cheap natural gas. Methane, the primary component of natural gas, has found widespread use as a fuel for electricity generation; however it is not a good feedstock for the production of chemicals or transportation fuels such as gasoline or diesel. This stems from the difficulty in selectively oxidizing methane by insertion of an oxygen atom into a strong carbon-hydrogen bond while preventing the complete combustion to carbon dioxide and water. Gold is known to be inert when exposed to oxygen or air, but when it divided into small nanoparticles, it starts to catalyze the oxidation of carbon monoxide. Dr. Grabow of the University of Houston and Dr. Chandler of Trinity University have recently discovered a mechanism whereby water acts as a co-catalyst during CO oxidation over gold nanoparticles supported on titanium-oxide. They are now translating this knowledge to enable the partial oxidation of methane and other alkanes to form the corresponding alcohol. The team follows a collaborative and tightly coupled approach using computational and experimental studies to quantify the promotional effect of water on selective oxidation and to investigate the dominant reaction mechanism for oxygen insertion into carbon-hydrogen bonds. With over 7.72 trillion m3 of confirmed natural gas reserves, there is a huge incentive to develop commercially-viable methane conversion processes to benefit the U.S. economy and achieve national energy independence. The research activities are integrated with broad-reaching educational efforts at the K-12, undergraduate, graduate and professional level to broaden the participation of minority students and increase the retention of at-risk students at both participating universities. The University of Houston is a designated Hispanic-Serving Institution and has the most ethnically balanced student body of all major research institutions in the U.S. Trinity University provides research active undergraduate education to San Antonio and the South Texas region, which are largely populated by a traditionally underrepresented group in the STEM disciplines. Together, the principal investigators have a strong record for mentoring research projects for undergraduate, minority and female students.Dr. Lars Grabow of the University of Houston and Dr. Bert Chandler of Trinity University are funded by the Chemical Catalysis Program at NSF to study oxygen insertion reactions into carbon-hydrogen (C-H) bonds over supported gold catalysts. The ultimate goal is to convert methane to methanol selectively, and a rational approach to the problem requires the close integration of theoretical (Grabow) and experimental (Chandler) techniques. The prevailing challenge in all processes using methane as a feedstock is activating the strong C-H bond; hence, the initial focus is on higher alkanes with weaker C-H bonds to acquire pertinent knowledge about the oxygen (O) insertion mechanism. To realize the possibility of using small amounts of water to improve the activity and selectivity of oxidation reactions over supported gold (Au) catalysts, the team quantifies the amount of surface water on different supports, investigates the dominant reaction mechanism for oxygen insertion into C-H bonds, and improves the product yield as guided by computational predictions. The selected application, O insertion into C-H bonds of alkanes, is a challenging fundamental problem in chemistry with far reaching technological impact for upgrading of natural gas to benefit the U.S. economy and achieve national energy independence. This concept can also be extended to other difficult selective oxidation reactions, e.g. ethylene epoxidation. Research activities are integrated with broad-reaching educational efforts at the K-12, undergraduate, graduate and professional level to broaden the participation of minority students and increase the retention of at-risk students at both participating universities. Together, the principal investigators have a strong record for mentoring research projects for undergraduate, minority and female students.