CAREER: Engineering Circular Hydrocarbon Reactions in Zeolite-based Catalysts

将塑料垃圾分解并将分解后的产品再制造成有价值的燃料和化学品的化学过程，对于航空燃料等难以脱碳的行业来说，是化石燃料的有吸引力的替代品。这种塑料上循环尤其有价值，因为它可以在中等温度下实现节能工艺。催化剂提供了一条实现这一目标的途径，方法是降低反应温度，并有选择地引导塑料转化为产品，这些产品可用作各种燃料、消费品、药品和建筑材料的基础材料。沸石是一类特别适合废塑料解构的多孔晶型催化剂，但要提高其效率、产品选择性和耐久性还需进一步研究和开发。因此，本项目调查了影响沸石催化剂分解一类普遍存在的废塑料聚烯烃的总体效率的关键设计因素。该项目得到了主要针对本科生和研究生的综合教育和推广活动的支持。尽管催化剂在燃料和重要化学中间体的生产中普遍存在，但具有高反应性、选择性和稳定性的先进催化剂的设计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。这里，这种合理的设计被应用于使用双功能金属/沸石催化剂的聚烯烃加氢裂化，其中沸石空穴同时提供了高反应活性和定制的选择性，但由于大体积产品的扩散限制，限制了催化剂的效率和稳定性。具有杂化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及性，但对反应和失活机制的直接影响，特别是这些复杂的多相体系，还没有得到很好的证实。因此，该项目的目标是在废聚烯烃的选择性加氢裂化中设计分级(双功能)沸石，其基础是假设分级结构的增强不仅影响简单的扩散影响，还包括孔结构(即沸石骨架)、连通性、连通性(金属：酸平衡/邻近)以及在介孔区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路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用于将废聚烯烃转化为有用产品的分级双功能催化剂的性能。这些见解将有助于理解整个催化生命周期，包括可以扩展的具体机理细节，以提高与碳氢化合物和含氧物加工(即生物质、可再生醇或二氧化碳)和不同沸石或沸石结构相关的各种原料的反应的催化剂效率。该奖项的研究成果将被主动纳入一门名为绿色与催化化学的本科生选修课，该选修课将包括互动部分，如动手催化(塑料上行循环和水污染物降解)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“可持续发展聚焦”。该项目还将通过在不同大学的催化实验室为更年轻的研究生提供“CatChat”来加强更广泛的催化社区。这些见面会将通过最初的虚拟联系创建一个相互支持的同行网络，并将在会议、研讨会和其他面对面的场所扩大。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。

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.