CAREER: Mechanistic Understanding and Strategies to Improve the Regeneration of Supported Nickel Catalysts for Methane Conversion

尽管对能源的需求不断增加，但全球变暖的加速已经产生了减少温室气体排放的迫切需要。在美国，天然气燃烧已成为第一大发电来源。然而，与天然气燃烧相关的二氧化碳（CO2），以及开采和运输过程中的甲烷排放，仍然导致温室气体排放超出了能源可持续发展所需的水平。两项技术——气制液（GTL）和催化甲烷热解（CMP）——有望在减少温室气体排放的同时，为燃料和化学品制造生产氢气。然而，由于碳沉积和金属烧结导致的催化剂失活仍然是甲烷增值反应的主要挑战。以往的研究并没有深入探索基于过程的催化剂失活和再生机制，从而设计出节能、有效的再生策略。为此，该项目将直接解决原型支撑镍（Ni）催化剂再生方面的基础知识空白，为延长甲烷催化剂的使用寿命提供新的选择，从而有助于更好的碳管理，并在向可持续燃料和化学品过渡的过程中进一步减少温室气体排放。虽然废甲烷转化金属催化剂的再生已经从现象上进行了描述，但对碳气化和金属再分散缺乏全面的基本理解。这部分是由于传统的多相催化研究方法主要关注催化剂表面吸附分子的催化反应动力学和动力学，而不是固体催化剂的结构动力学。该项目将结合最先进的原位环境透射电子显微镜（ETEM）和机器学习的一个分支，即计算机视觉，直接监测再生条件下的碳沉积和Ni催化剂结构变化。对废金属催化剂再生的基本认识将通过三个目标来实现：1)建立再生性能和结构演变的高通量相关性的operando方法；2)确定碳气化机制和优化气化条件的动力学；3)确定循环反应再生过程的金属再分散机制和支撑效应。这三个目标的成功整合将建立气化动力学与催化剂在脱碳、气化诱导烧结和Ni再分散过程中的状态之间的直接关联。这种相关性可以使再生条件参数的合理调整达到完全脱碳和有效的镍催化剂再分散。这些对废镍催化剂再生的基本见解可以为其他负载金属催化剂体系提供新的实用再生策略。除了项目的技术方面，研究者将建立一个跨学科的、实用的、鼓舞人心的项目“纳米催化剂的惊人生命周期”。该项目将通过将研究与教育相结合的活动、激发学生和K-12教师对STEM领域的兴趣和灵感的互动研讨会，以及吸引和招募代表性不足的学生进入工程领域的推广工作，培养新一代的催化学生。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。

The acceleration of global warming has produced a pressing need to reduce greenhouse gas emissions despite the ever-increasing demand for energy. In the United States, natural gas combustion has become the No. 1 source of electricity generation. However, the carbon dioxide (CO2) associated with natural gas combustion, combined with methane emissions during its extraction and transport, still contributes to greenhouse gas emissions beyond levels required for energy sustainability. Two technologies - gas-to-liquids (GTL) and catalytic methane pyrolysis (CMP) – hold promise for producing hydrogen for both fuel and chemicals manufacturing while decreasing greenhouse gas emissions. However, catalyst deactivation due to carbon deposition and metal sintering are still major challenges in methane valorization reactions. Previous research studies have not explored process-based catalyst deactivation and regeneration mechanisms in sufficient depth to devise energy-efficient, effective regeneration strategies. To that end, the project will directly address fundamental knowledge gaps in the regeneration of prototypical supported nickel (Ni) catalysts to enable new options for extending methane catalyst lifetime, thus contributing to better carbon management and further reduction of greenhouse gas emissions during the transition to sustainable fuels and chemicals. Although the regeneration of spent methane conversion metal catalysts has been described phenomenologically, a comprehensive fundamental understanding of carbon gasification and metal redispersion has been lacking. This is partly due to conventional investigation methodologies in heterogeneous catalysis that focus mainly on the catalytic reaction kinetics and dynamics of molecules adsorbed on catalyst surfaces, not on the structural dynamics of solid catalysts. The project will combine state-of-the-art, in-situ environmental transmission electron microscopy (ETEM) with a branch of machine learning known as computer vision to directly monitor both carbon deposits and Ni catalyst structural changes under regeneration conditions. Advancement of fundamental understanding of spent metal catalyst regeneration will be achieved through three aims: 1) establish an operando methodology for high-throughput correlation of regeneration performance and structural evolution, 2) determine carbon gasification mechanisms and kinetics for optimized gasification conditions, and 3) determine metal redispersion mechanisms and support effects enabling a cyclic reaction-regeneration process. Successful integration of the three aims will establish direct correlations between the gasification kinetics and state of the catalyst during the carbon removal, gasification-induced sintering, and Ni redispersion sequence. The correlations will enable rational tuning of regeneration condition parameters to achieve complete carbon removal and effective Ni catalyst redispersion. These fundamental insights into rejuvenating spent Ni catalysts can lead to new practical regeneration strategies for other supported metal catalyst systems. Beyond the technical aspects of the project, the investigator will establish an interdisciplinary, practical, and inspiring program “The Amazing Life Cycle of Nanocatalysts.” The program will train a new generation of students in catalysis through activities integrating research into education, interactive workshops that excite and inspire students and K–12 teachers about STEM fields, and outreach efforts attracting and recruiting underrepresented students to engineering.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.