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教授将研究使用精心结构的基于IrO 2的混合金属氧化物进行选择性甲烷氧化。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，并将产生重大的经济和环境效益。新的具有成本效益的甲烷制化学品工艺的可用性可以激励页岩和天然气作为化学原料而不是燃烧燃料的使用，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方法很少，不适合商业用途。主要的困难是大多数催化材料必须在高温下操作以引发甲烷的化学转化，而需要温和的条件来引导随后的化学反应朝向期望的产物。在这个项目中，研究人员将开发甲烷选择性转化为更有价值的化学品使用定义明确的氧化物催化剂的基本理解。设计具有原子级精度的催化剂结构对于有效和选择性地将甲烷转化为化学品是必要的。研究人员将为高中和本科生提供参与研究的机会，并专注于招募代表性不足的群体的学生参与这些活动。这些外联活动旨在促进科学、技术、工程和数学学科。该项目旨在从根本上了解IrO 2基混合金属氧化物的局部结构和组成如何影响甲烷的氧化化学，并可定制以促进甲烷选择性氧化为增值产品，如乙烯，甲醛或其他有机含氧化合物。关键的想法是，原子分散的IrO 2-网站在一个反应性较低的氧化物将诱导初始甲烷活化在低温下，随后转化为产品将介导的第二个，更化学选择性的氧化物。本研究涉及IrO 2改性的TiO 2和RuO 2制备的平面晶体表面以及纳米晶粉末的结构和化学性质的调查。两个一般的结构图案正在研究中，即，Ir原子取代到主机氧化物的表面晶格和纳米级IrO 2岛分散在主机氧化物表面上。这些材料将使用实验和理论方法相结合的研究，包括真空表面科学和催化剂表征，反应器研究和密度泛函理论和动力学蒙特卡罗建模。该项目的主要目标是系统地表征不同组成和形态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。该项目将第一原理模型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，以发展对甲烷在混合金属氧化物上的选择性氧化的强大理解。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。

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.