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，天然气燃烧已成为头号发电来源。然而，与天然气燃烧相关的二氧化碳(CO2)，再加上其开采和运输过程中的甲烷排放，仍会导致温室气体排放量超过能源可持续性所需的水平。两种技术--气转液(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价化反应中的主要挑战。以前的研究还没有对基于过程的催化剂失活和再生机理进行足够深入的探索，以设计出节能、有效的再生策略。为此，该项目将直接解决原型负载型镍(镍)催化剂再生方面的基本知识空白，以实现延长甲烷催化剂寿命的新选择，从而有助于更好地进行碳管理，并在向可持续燃料和化学品过渡期间进一步减少温室气体排放。尽管废甲烷转化金属催化剂的再生已经被现象学地描述了，但对碳气化和金属再分散还缺乏全面的基础了解。这在一定程度上是由于多相催化的传统研究方法，主要集中在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。该项目将把最先进的原位环境传输电子显微镜(ETEM)与机器学习的一个分支计算机视觉结合起来，直接监测再生条件下碳沉积和镍催化剂结构的变化。通过以下三个目标推动对废金属催化剂再生的基本理解：1)建立再生性能和结构演变的高通量关联的操作方法；2)确定优化气化条件下的碳气化机制和动力学；3)确定金属再分散机制和支持循环反应-再生过程的效果。这三个目标的成功结合将在脱碳、气化诱导烧结和镍再分散过程中建立气化动力学和催化剂状态之间的直接关联。这些关联式将使合理调整再生条件参数，以实现完全脱碳和有效的镍催化剂再分散。这些对再生废镍催化剂的基本见解可以为其他负载型金属催化剂系统带来新的实用再生策略。除了项目的技术方面，研究人员还将建立一个跨学科的、实用的和鼓舞人心的计划--“纳米催化剂惊人的生命周期”。该计划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领域的兴奋和启发的互动研讨会，以及吸引和招募代表不足的学生从事工程设计的外联努力，在催化领域培训新一代学生。该奖项反映了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。

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.