CAREER: Engineering Circular Hydrocarbon Reactions in Zeolite-based Catalysts

对于航空燃料等难以脱碳的行业来说，分解塑料废物并将分解后的产品重新制造成有价值的燃料和化学品的化学工艺是化石燃料的有吸引力的替代品。这样的塑料升级回收是特别有价值的，当它可以在适度的温度下实现节能工艺。催化剂通过降低反应温度，有选择地将塑料转化为各种燃料、消费品、药品和建筑材料的基本原料，为实现这一目标提供了一条途径。沸石是一类特别适用于废塑料解构的多孔晶体催化剂，但其效率、产品选择性和耐久性有待进一步的研究和开发。因此，本项目研究了影响沸石催化剂分解常见废塑料聚烯烃整体效率的关键设计因素。该项目得到主要针对本科生和研究生的综合教育和推广活动的支持。虽然催化剂在燃料和重要的化学中间体生产中无处不在，但设计具有高反应性、选择性和稳定性的先进催化剂对于有效和可持续地减少污染，同时降低能源需求和减少碳排放仍然至关重要。在这里，这种合理的设计被用于使用双功能金属/沸石催化剂的聚烯烃加氢裂化，其中沸石空隙同时提供了高反应活性和定制的选择性，但由于大体积产物的扩散限制，限制了催化剂的效率和稳定性。具有混合孔结构的分级沸石可以用来解决大体积聚合物分子的不可接近性，但对反应和失活机制的直接影响，特别是对这些复杂的多相体系的直接影响尚不明确。因此，该项目旨在设计分级（双功能）沸石，用于废聚烯烃的选择性加氢裂化，基于以下假设：分级结构的增强会影响聚烯烃裂化的反应和失活速率，而不仅仅是简单的扩散影响，还包括孔隙结构（即沸石框架）、连连性、通信（金属：酸平衡/接近）以及介孔区域和表面质子内发生的反应的影响。通过将合成方案与详细的反应途径和失活分析相结合，该项目将揭示形状选择性和传输现象如何影响这些分层双功能催化剂将废聚烯烃转化为有用产品的性能。这些见解将有助于理解整个催化生命周期，包括具体的机理细节，这些细节可以扩展到提高与碳氢化合物和氧合物处理（即生物质，可再生醇或CO2）相关的各种原料反应的催化剂效率，以及不同的沸石或沸石型结构。该奖项的研究成果将被积极纳入本科选修课“绿色与催化化学”中，该选修课将包括互动部分，如实际催化（塑料升级回收和水污染物降解）和分离（二氧化碳捕获）实验，以及基于涵盖能源和气候相关主题的媒体文章的“可持续发展焦点”。该项目还将通过为各大学催化实验室的年轻研究生提供“CatChats”来加强更广泛的催化社区。通过最初的虚拟联系，这些聚会将创建一个支持性的同行网络，并将在会议、研讨会和其他面对面的场所扩展。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。

Chemical processes that breakdown plastic waste and remanufacture the deconstructed products to valuable fuels and chemicals are attractive alternatives to fossil-fuels for hard-to-decarbonize sectors such as aviation fuels. Such plastic upcycling is especially valuable when it can be achieved at moderate temperatures in energy efficient processes. Catalysts offer a route to that end by lowering reaction temperature and selectively directing conversion of plastic to products that serve as building blocks for a broad range of fuels, consumer goods, pharmaceuticals, and building materials, to name a few. Zeolites are a class of porous crystalline catalysts that are especially suitable for waste plastic deconstruction, but further research and development is needed to improve their efficiency, product selectivity, and durability. Thus, this project investigates key design factors that affect the overall effectiveness of zeolite catalysts for the breakdown of a prevalent class of waste plastic, polyolefins. The project is supported by integrated educational and outreach activities aimed primarily at undergraduate and graduate students.While catalysts are ubiquitous in the production of fuels and important chemical intermediates, the design of advanced catalysts that possess high reactivity, selectivity, and stability remains paramount for efficiently and sustainably abating pollution while lowering energy demands and decreasing carbon emissions. Here, this rational design is employed in the hydrocracking of polyolefins using bifunctional metal/zeolite catalysts, where zeolitic voids simultaneously provide high reactivity and tailored selectivity, but limit catalyst efficiency and stability due to diffusional constraints of bulky products. Hierarchical zeolites with hybrid pore structures can be utilized to address this inaccessibility of bulky polymer molecules, but the direct effect on reaction and deactivation mechanisms, especially of these complex multiphase systems is not well-established. The project thus aims to engineer hierarchical (bifunctional) zeolites in selective hydrocracking of waste polyolefins, based on hypotheses that enhancements of hierarchical structuring affect reaction and deactivation rates for polyolefin cracking beyond simple diffusional impacts and include effects of pore structure (i.e., zeolite framework), connectivity, communication (metal:acid balance/proximity) and reactions occurring within the mesoporous regions and surface protons. By combining synthetic protocols with detailed reaction pathway and deactivation analysis, the project will reveal new insights on how shape-selectivity and transport phenomena affect the performance of these hierarchical, bifunctional catalysts for transformation of waste polyolefins into useful products. Those insights will aid in understanding the entire catalytic lifecycle, including specific mechanistic details that can be extended to improve catalyst efficiency for reactions of various feedstocks related to hydrocarbon and oxygenate processing (i.e., biomass, renewable alcohols, or CO2) and different zeolite or zeotype architectures. Research results from this award will be proactively incorporated into an undergraduate elective entitled Green and Catalytic Chemistry that will incorporate interactive components like hands-on catalysis (plastic upcycling and aqueous pollutant degradation) and separation (CO2 capture) experiments, and “Sustainability Spotlights” based on media articles covering energy and climate related topics. The project will also strengthen the broader catalysis community through “CatChats” for younger graduate students in catalysis labs at various universities. These meetups will create a supportive network of peers, via initial virtual connections that will be expanded at conferences, workshops, and other in-person venues.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.