CAREER: Cation and Nanoparticle Interconversion in Metal-Exchanged Zeolites

小孔、微晶沸石材料广泛应用于化学和燃料工业，用于需要分子尺度捕获、分离或催化反应的过程。在催化的情况下，沸石通常与极小的催化金属颗粒（甚至单个原子）结合使用，这些金属颗粒分散在沸石结构中的纳米级孔和空隙中。所得到的催化剂对促进特定的催化反应非常有效，同时有效地利用少量昂贵的金属，如铂或钯。然而，与许多催化反应相关的恶劣条件导致金属颗粒团聚和伴随的催化剂效率损失。该项目开发计算分子模型和理论，预测沸石支持的金属团聚和再分散的动力学。此外，该模型还包括设计和合成特征，可以阻止金属原子和颗粒在反应条件下团聚，从而提高广泛用于石化和排放相关应用的催化剂的能效。通过与强调K-12女孩编程的当地组织合作，以及组织解决国际和国内本科和研究生工程专业学生面临的社会和专业发展挑战的活动，该项目与在STEM管道的多个点上解决代表性不足社区保留问题的努力相结合。该项目开发了原子模型，描述了沸石成分、气体条件、纳米颗粒大小和分布如何影响沸石中阳离子和纳米颗粒相互转化的热力学和动力学。主要目标是1)模拟沸石支持的铂和钯阳离子和纳米颗粒相互转化的热力学，2)预测催化相关的反应物气体如何促进或阻碍相互转化，3)确定沸石包封如何调节纳米颗粒的结构和能量，以及4)确定控制阳离子和纳米颗粒相互转化动力学的基本过程。这些目标将通过使用分子建模工具来实现，包括密度泛函理论、波函数理论、经典力场和蒙特卡罗模拟。该项目将为催化和沸石合成前沿挑战——抗失活沸石的工程设计提供指导。此外，该项目将实现沸石组成和合成策略的变革预测，从而稳定催化剂在反应环境中的性能。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。

Small pore, microcrystalline zeolite materials are widely used in the chemicals and fuels industries for processes where molecular-scale capture, separation, or catalytic reaction is needed. In the case of catalysis, zeolites are often used in conjunction with extremely small particles of catalytic metals – or even individual atoms – dispersed throughout the nanoscale pores and voids in the zeolite structure. The resulting catalysts are highly effective for promoting specific catalytic reactions, while efficiently utilizing small amounts of expensive metals such as platinum or palladium. Nevertheless, the harsh conditions associated with many catalytic reactions results in metal particle agglomeration and concomitant loss of catalyst efficiency. The project develops computational molecular models and theory predicting the dynamics of agglomeration and redispersion of metals supported by zeolites. In addition, the models include design and synthesis features that deter the agglomeration of metal atoms and particles under reaction conditions, thus improving the energy efficiency of catalysts widely used for petrochemical and emissions related applications. The project is integrated with efforts that address retention of underrepresented communities at multiple points in the STEM pipeline, through collaboration with local organizations that emphasize coding for girls in K-12, and by organizing events that address social and professional development challenges faced by both international and domestic undergraduate and graduate engineering students. The project develops atomistic models that describe how zeolite composition, gas conditions, and nanoparticle size and distribution affect the thermodynamics and kinetics of cation and nanoparticle interconversion in zeolites. The main objectives are to 1) model the thermodynamics of zeolite-supported platinum and palladium cation and nanoparticle interconversion, 2) predict how catalytically relevant reactant gases promote or impede interconversion, 3) determine how zeolite encapsulation modulates the structure and energy of nanoparticles, and 4) determine the fundamental processes that govern the kinetics of interconversion between cations and nanoparticles. These objectives will be fulfilled by using molecular modeling tools that include density functional theory, wave function theory, classical forcefields, and Monte Carlo simulations. This project will provide guidance on the engineering of deactivation resistant zeolites, a challenge at the frontiers of catalysis and zeolite synthesis. Further, the project will enable transformative predictions of zeolite compositions and synthetic strategies that stabilize catalyst performance in the reaction environment.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.