Collaborative Research: The role of oxide overlayers on adsorbate migration and metal sintering in reactions of CO2

合作研究：氧化物覆盖层对 CO2 反应中吸附物迁移和金属烧结的作用

• 批准号: 2152391
• 负责人: Kerry Dooley
• 金额: $ 30.23万
• 依托单位: Louisiana State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-10-01 至 2025-09-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2152391&HistoricalAwards=false
• 关键词: Collaborative; Research; role; oxide; overlayers

Combustion of natural gas (chiefly comprised of methane, i.e., CH4) provides a major portion of our nation’s energy needs. Although methane is a relatively “clean” fossil fuel, its combustion produces carbon dioxide (CO2) which constitutes the major component of greenhouse gas (GHG) emissions. Methane can also be reacted with steam (H2O) to produce carbon monoxide (CO) and hydrogen (H2) in a process known as methane steam reforming. The product CO and H2 gases are further reacted to produce a wide range of fuels and chemicals. The project investigates an alternative approach – “dry” reforming of methane (DRM) - which utilizes captured CO2, rather than steam, to generate CO and H2, thus decreasing the overall GHG inventory. Methane reforming, via any technology, is an energy intensive process. Catalysts are utilized to reduce operating temperatures, improve process efficiency, and drive the reactions to desired products. Dry reforming is even more challenging than steam reforming, thus creating a need for research aimed at identifying more active and selective catalysts that are stable under high-temperature reaction conditions. The project addresses those needs by combining theoretical, computational, and experimental methods to identify effective DRM catalysts. In addition, the project will investigate economics of DRM technology, and incorporate educational and outreach activities exposing high-school and undergraduate students to the field of chemical engineering – so important to the fuels, chemicals, and environmental industries. DRM catalysts must operate at high temperatures, which can destroy carefully designed synthetic structures or promote secondary reactions (e.g., reverse water-gas shift reaction (RWGS) and coke formation) that result in lower value products. One mechanism associated with both the primary and secondary processes is the ability of some catalysts to store and release oxygen during different parts of the cycle. Other catalysts can avoid this oxygen-centric route at the expense of higher activation energies. This work develops hybrid catalysts, using both reducible and non-reducible oxides, to combine the best properties of both in generating highly stable and chemically selective methane reforming catalysts which can be used to operate at industrially relevant conditions. The simultaneous methane reforming and RWGS reactions over ceria catalysts occur through mobile oxygen species. Non-reducible catalyst overlayers have the potential to limit hydrogen spillover from the active metal sites, preventing the unwanted secondary reaction and stabilizing the carefully designed catalyst structure without limiting the role of oxygen in the methane reforming. Using a combination of simulation (density functional theory) and experimental work, the project will develop highly active and structurally stable catalysts while limiting the undesired RWGS, which decreases the H2:CO ratio. However, subsequent reactions to make chemicals require higher H2-to-CO ratios than are possible under standard dry reforming conditions. As such, the optimized hierarchical catalysts will be tested under harsh conditions in the presence of low concentrations of water (i.e., a steam/CO2 “bi-reforming” process) to further increase the H2-to-CO ratio.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.

天然气（主要由甲烷组成，即CH4）的燃烧提供了我国能源需求的主要部分。虽然甲烷是一种相对“清洁”的化石燃料，但其燃烧产生的二氧化碳（CO2）是温室气体（GHG）排放的主要成分。甲烷也可以与水蒸气（H2O）反应生成一氧化碳（CO）和氢气（H2），这一过程被称为甲烷蒸汽重整。产物CO和H2气体进一步反应，产生各种各样的燃料和化学品。该项目研究了另一种替代方法——甲烷“干式”重整（DRM）——利用捕获的二氧化碳而不是蒸汽来生成CO和H2，从而减少温室气体总量。无论采用何种技术，甲烷重整都是一个能源密集型的过程。催化剂用于降低操作温度，提高工艺效率，并推动反应产生所需的产品。干式重整比蒸汽重整更具挑战性，因此需要研究在高温反应条件下稳定的更具活性和选择性的催化剂。该项目通过结合理论、计算和实验方法来确定有效的DRM催化剂，以满足这些需求。此外，该项目将调查DRM技术的经济学，并结合教育和推广活动，使高中生和大学生接触化学工程领域——这对燃料、化学品和环境工业非常重要。DRM催化剂必须在高温下工作，这可能会破坏精心设计的合成结构或促进二次反应（例如逆水气转换反应（RWGS）和焦炭形成），从而导致低价值产品。与一级和二级过程相关的一个机制是一些催化剂在循环的不同部分储存和释放氧气的能力。其他催化剂可以以更高的活化能为代价来避免这种以氧为中心的路线。这项工作开发了混合催化剂，使用可还原和不可还原的氧化物，结合两者的最佳性能，产生高度稳定和化学选择性的甲烷重整催化剂，可用于工业相关条件下的操作。氧化铈催化剂上的甲烷重整和RWGS反应是通过流动氧进行的。不可还原的催化剂覆盖层有可能限制氢从活性金属位点溢出，防止不必要的二次反应，稳定精心设计的催化剂结构，而不限制氧气在甲烷重整中的作用。通过模拟（密度泛函数理论）和实验工作的结合，该项目将开发出高活性和结构稳定的催化剂，同时限制不理想的RWGS，从而降低H2:CO比。然而，随后的化学反应需要比标准干重整条件下更高的h2 - co比。因此，优化后的分级催化剂将在低浓度水存在的恶劣条件下进行测试（即蒸汽/二氧化碳“双重整”过程），以进一步提高H2-to-CO比。该奖项反映了美国国家科学基金会的法定使命，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。