CAS: IrO2 Based Mixed Metal Oxides for the Selective Oxidation of Methane

在化学系化学催化项目的资助下，佛罗里达大学的Weaver、Hagelin-Weaver和Hibbitts教授将研究使用结构精细的IrO2基混合金属氧化物进行甲烷选择性氧化。开发高效的催化工艺，将页岩和天然气的主要成分甲烷转化为更有价值的产品，对化学工业来说是一个巨大的挑战，将产生显著的经济和环境效益。新的、具有成本效益的甲烷转化为化学品的过程的可获得性，可以鼓励使用页岩和天然气作为化学原料，而不是燃烧燃料，从而减少温室气体排放，并促进向可再生能源的过渡。目前，将甲烷转化为化学品的直接催化过程很少，不适合商业使用。主要的困难是，大多数催化材料必须在高温下操作才能引发甲烷的化学转化，而需要更温和的条件来引导后续的化学反应产生理想的产品。在这个项目中，研究人员将对使用定义明确的氧化物催化剂选择性地将甲烷转化为更有价值的化学品有一个基本的了解。设计具有原子级精度的催化剂结构对于高效和选择性地将甲烷转化为化学品是必要的。调查人员将为高中生和本科生提供参与研究的机会，并专注于从代表性不足的群体中招募学生参与这些活动。这些外联活动旨在促进科学、技术、工程和数学(STEM)学科的发展。该项目旨在对以IrO2为基础的混合金属氧化物的当地结构和组成如何影响甲烷的氧化化学有一个基本的了解，并可根据需要促进甲烷选择性氧化成增值产品，如乙烯、甲醛或其他有机含氧物。关键的想法是，原子分散在活性较低的氧化物中的IrO2-位将在低温下诱导甲烷的初始活化，随后转化为产物的过程将由第二个更具化学选择性的氧化物介导。本研究主要研究了平面晶面的IrO2修饰的二氧化钛和RuO2以及纳米晶粉末的结构和化学性质。研究了两种常见的结构基元，即Ir原子被替换到主体氧化物的表面晶格中和纳米级的IrO2岛分散在主体氧化物表面。这些材料将采用实验和理论相结合的方法进行研究，包括超高真空表面科学和催化剂表征，反应堆研究和密度泛函理论和动力学蒙特卡罗模拟。该项目的主要目标是系统地表征不同组成和形貌的混合金属氧化物表面的原子级结构，并确定甲烷氧化化学如何受到局部Ir-O结构的影响。该项目涉及将第一性原理建模的结果与从平面晶体表面和更复杂的纳米颗粒获得的实验结果进行严格的比较，以发展对混合金属氧化物上甲烷选择性氧化的强有力的理解。这一奖项反映了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。

With funding from the Chemical Catalysis program in the Division of Chemistry, Professors Weaver, Hagelin-Weaver and Hibbitts of the University of Florida will study selective methane oxidation using elaborately structured IrO2-based mixed metal oxides. Developing efficient catalytic processes to transform methane, the primary component of shale and natural gas, to more valuable products is a grand challenge for the chemical industry and would have significant economic and environmental benefits. The availability of new and cost-effective methane-to-chemicals processes could incentivize the use of shale and natural gas as a chemical feedstock rather than a combustion fuel, thereby mitigating greenhouse gas emissions and facilitating a transition toward renewable energy. Currently, direct catalytic processes to convert methane to chemicals are scarce and unsuitable for commercial use. The major difficulty is that most catalytic materials must operate at high temperatures to initiate chemical conversions of methane, whereas milder conditions are needed to direct the subsequent chemistry toward desirable products. In this project, the investigators will develop a fundamental understanding of the selective conversions of methane to more valuable chemicals using well-defined oxide catalysts. Designing the catalyst structures with atomic-level precision is necessary for efficiently and selectively converting methane to chemicals. The investigators will provide opportunities for high school and undergraduate students to participate in their research, and focus on recruiting students from underrepresented groups to engage in these activities. These outreach activities seek to promote the science, technology, engineering and math (STEM) disciplines. This project seeks to develop a fundamental understanding of how the local structure and composition of IrO2-based mixed metal oxides influence the oxidation chemistry of methane, and may be tailored to promote the selective oxidation of methane to value-added products, such as ethylene, formaldehyde or other organic oxygenates. The key idea is that atomically dispersed IrO2-sites in a less reactive oxide will induce initial methane activation at low temperature and that subsequent conversion to products will be mediated by the second, more chemically selective oxide. This research involves investigations of the structural and chemical properties of IrO2-modified TiO2 and RuO2 prepared as planar crystalline surfaces as well as nanocrystalline powders. Two general structural motifs are being investigated, namely, Ir atoms substituted into the surface lattice of the host oxide and nanoscopic IrO2 islands dispersed on the host oxide surface. These materials will be investigated using a combination of experimental and theoretical methods including ultrahigh vacuum surface science and catalyst characterization, reactor studies and density functional theory and kinetic Monte Carlo modeling. Key aims of the project are to systematically characterize the atomic-level structures of mixed metal-oxide surfaces of varying composition and morphology and determine how the methane oxidation chemistry is influenced by the local Ir-O structures. The project involves stringent comparisons of the results of first-principles modeling with experimental results obtained from planar crystalline surfaces and more complex nanoparticles to develop a robust understanding of the selective oxidation of methane on the mixed metal-oxides.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.