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Diagnosing Surface Versus Bulk Reactivity for Molecular Catalysis Within Metal-Organic Frameworks Using a Quantitative Kinetic Model

preprint
submitted on 07.05.2020 and posted on 08.05.2020 by Ben A Johnson, Sascha Ott

Metal-organic frameworks (MOFs) are becoming increasingly popular as heterogenous support matrices for molecular catalysts. Given that reactants, or potentially holes/electrons, need to diffuse into the porous framework as the reaction proceeds, the reaction can possibly take place within the bulk of the particle or be confined to a thin layer at the surface due to transport limitations. Herein, a simple steady-state reaction-diffusion kinetic model is developed to diagnose these two mutually exclusive behaviors in MOF-based systems. The oxygen evolution reaction (OER) driven by a chemical oxidant is presented as an example mechanism. Quantitative metrics for assigning either bulk or surface reactivity are delineated over a wide variety of conditions, and numerical simulations are employed to verify these results. For each case, expressions for the turnover frequency (TOF) are outlined, and it is shown that surface reactivity can influence measured TOFs. Importantly, this report shows how to transition from surface to bulk reactivity and thus identifies which experimental parameters to target for optimizing the efficiency of MOF-based molecular catalyst systems.


Funding

ERC-CoG2015-681895_MOFcat

History

Email Address of Submitting Author

ben.johnson@kemi.uu.se

Institution

Uppsala University

Country

Sweden

ORCID For Submitting Author

0000-0002-6570-6392

Declaration of Conflict of Interest

No Conflicts of Interest

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