EAGER: Fe/Mn-Containing Perovskite Oxides Promoted by Alkali Metal Molybdates for Chemical-Looping Catalysis – Thin-Film Preparation and Surface Characterization

天然气是生产烯烃的关键原料，烯烃广泛用于高分子材料的化工生产。乙烯和丙烯的生产是化工行业最耗能的过程之一，每年排放超过3亿吨的二氧化碳。该项目探索了一种替代目前工业实践的化学环氧化脱氢（CL-ODH）方法。与传统ODH相比，CL-ODH具有显著提高能源效率和降低碳排放的潜力。该项目的重点是提高CL-ODH催化剂材料的性能和耐用性，从基本层面上了解它们的工作机制，并利用这些了解来优化催化剂设计。本项目重点研究碱金属钼酸盐促进钙钛矿氧化物的机理，特别是Na2MoO4、Na2Mo2O7或K2MoO4促进乙烷和丙烷CL-ODH的La0.8Sr0.2FeO3和La0.7Ca0.3MnO3。CL-ODH概念有可能大大加强轻质烯烃的生产。研究小组此前发现，钼酸盐促进钙钛矿氧化物形成核壳结构，其中含Mn/ fe的钙钛矿氧化物核促进活性晶格氧储存/交换，熔融钼酸盐壳促进选择性C-H键活化和氧化转化。该项目首次深入研究了这种新型氧化还原催化剂体系的核心、壳层和活性物质的作用。该项目旨在通过制备薄膜模型催化剂和使用各种表面科学工具进行广泛的表征来揭示CL-ODH反应的潜在机制。在市售的SrTiO3上通过聚合物辅助沉积制备La0.8Sr0.2FeO3和La0.7Ca0.3MnO3外延生长薄膜。随后依次进行MoO3和Na/K的MBE沉积，以及O2环境处理。薄膜的生长将在现场进行监测并随后进行表征。本文将对含和不含碱金属钼酸盐的钙钛矿薄膜样品进行机理研究和反应性测试，以建立合理的氧化还原催化剂优化方法。研究结果将被纳入研究者的教学中。通过北卡罗莱纳州立大学的凯南奖学金项目，高中教师将参与该项目，以激发学生对STEM职业的兴趣。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。

Natural gas is a key raw material for production of olefins used extensively for the chemical manufacture of polymeric materials. Production of ethylene and propylene is among the most energy-intensive processes in the chemical sector, emitting more than 300 million tons of carbon dioxide each year. The project explores an alternative to current industry practice known as chemical-looping oxidative dehydrogenation (CL-ODH). CL-ODH has potential to substantially increase energy efficiency and lower carbon emissions compared to conventional ODH. The project focuses on improving the performance and durability of CL-ODH catalyst materials by understanding – at a fundamental level – the mechanism by which they work, and by using that understanding to optimize catalyst design. The project focuses on the mechanistic aspects of alkali metal molybdate promoted perovskites oxides, specifically, Na2MoO4, Na2Mo2O7 or K2MoO4 promoted La0.8Sr0.2FeO3 and La0.7Ca0.3MnO3 for CL-ODH of ethane and propane. The CL-ODH concept has potential to greatly intensify light-olefin production. The research team has previously discovered that molybdate promoted perovskite oxides form a core-shell structure with the Mn/Fe-containing perovskite oxide core promoting active lattice oxygen storage/exchange, and the molten molybdate shell facilitating selective C-H bond activation and oxidative conversion. This project represents the first in-depth attempt to investigate the roles of the core, shell, and active species for this novel redox catalyst system. The project aims to unveil the underlying mechanisms for the CL-ODH reactions by preparing thin-film model catalysts and performing extensive characterizations using a variety of surface science tools. Epitaxially grown thin films of La0.8Sr0.2FeO3 and La0.7Ca0.3MnO3 will be prepared on commercially available SrTiO3 via polymer-assisted deposition. This is followed with sequential MBE deposition of MoO3 and Na/K, and O2 ambient treatment. The growth of the thin film will be monitored in situ and characterized afterwards. Mechanistic investigations and reactive testing will be performed on perovskite thin film samples both with and without alkali metal molybdates to establish a rational approach for redox catalyst optimization. Results from the project will be integrated in teaching by the investigators. Through the Kenan fellowship program at North Carolina State University, high school teachers will be involved in the project to stimulate students' interest towards STEM careers.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.