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<p>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.</p>
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Diagnosing Surface Versus Bulk Reactivity for Molecular Catalysis Within Metal-Organic Frameworks Using a Quantitative Kinetic Model
