CAS: Reaction and Deactivation Implications of Pore structure, Nodal Identity, and Coordination Environment on Small-molecule Oxidations by Metal-organic Frameworks

With the support of the Chemical Catalysis program in the Division of Chemistry, Michele L. Sarazen of Princeton University is studying selective oxidation reactions that are central in a variety of pharmaceutical, fine chemical, and other chemical industry processes. Specifically, this work is directed at the design of advanced catalysts with high reactivity, selectivity, and stability that can efficiently and sustainably address our growing energy and product demands through combined synthesis, characterization, and reaction analysis. Metal-organic frameworks (MOFs) are a class of materials attractive for many chemistries, including oxidations. This proposal aims to provide understanding of how MOFs behave under model operating conditions, their deactivation pathways, and their reactivation. If successful, the results of these studies will help guide further research, not only in catalysis but also for other applications such as gas capture and separations, energy storage, drug delivery, and sensors. Additional implications for commercial sustainability from understanding material limitations can improve existing materials in terms of thermochemical robustness and stability, and reducing waste from spent catalysts. Similarly, this work prioritizes sustainable practices by considering cheaper and more abundant metals and more benign oxidants compared to many current industrial processes. PI Sarazen will continue her engagement in scientific outreach and educational programs that aim to increase diversity within the scientific community through demonstrations in on-/off-campus outreach events that utilize these catalysts in the oxidation of dye molecules found in wastewater, offering exciting, vibrant color changes that can be used to promote the power of catalyst applications and public scientific literacy on sustainable industrial chemistry. This project involves the study of liquid-phase oxidation reactions valuable for industrial applications through experimental and computational characterizations. The regularly distributed metal centers in open crystalline MOF networks will be used to build structure-function relations and elucidate reaction and deactivation mechanisms during representative oxidation reactions of 1-octene, where rigorous kinetic experiments will be coupled with characterization techniques and computational modelling. Specifically, this proposed work will investigate physicochemically tunable Fe-based MIL MOFs during hydrogen peroxide-assisted oxidation of conformationally and synthetically modular 1-octene to quantify the impacts of pore hydrophobicity, acidity, and Fe active site coordination sphere perturbations on observed reactivity, selectivity, and stability. The results of this experimental study will motivate computational investigations with density functional theory by taking advantage of the crystalline nature of MOFs and could develop trends that predict promising material compositions or methods to improve existing materials for a desired application. The framework described here for studying entire catalytic lifecycles, including specific mechanistic details for oxidation reactions on Fe-carboxylate MOFs, has the potential to provide a foundation that can be extended to improve catalyst efficiency for other reactions of various feedstocks related to hydrocarbon and oxygenate processing from carbon upgrading (petroleum/biomass/waste refining) over different MOF architectures and even different energy (i.e., electrocatalytic, photocatalytic) inputs. 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.