Framework-Defined Microenvironments Differentiate Molecular CO2 Reduction Sites
Year: 2026
Type: preprint
Abstract: Molecular catalysts offer well-defined active sites for electrochemical CO2 reduction to CO, while immobilization in metal–organic frameworks (MOFs) can increase catalyst loading and organize these sites within a porous environment. This strategy often assumes that repeated molecular sites remain functionally equivalent after framework incorporation. Here, using DFT-benchmarked, site-resolved empirical valence bond–free energy perturbation (EVB–FEP) simulations in an explicit electrode-supported Co-porphyrin MOF, we studied four elementary CO2-to-CO reactions across eight matched boundary and inner sites and four progressively assembled electrochemical environments. Framework embedding produces the dominant energetic redistribution and establishes a persistent boundary–inner differentiation in CO2 adsorption. We identify its microscopic origin as a site-dependent local axial electric field generated by different balances of solvent, ion, and neighboring-framework electrostatics. Boundary and inner sites therefore stabilize the same reaction through different microscopic environments. Regional CO2 mobility further shows that intrinsic reactivity and transport accessibility provide separate constraints on site function. Together, these results show that framework incorporation creates a spatial distribution of functionally distinct catalytic microenvironments rather than simply multiplying an equivalent molecular catalyst. By combining high densities of well-defined molecular active sites with spatially heterogeneous yet synthetically tunable environments, framework materials provide a bridge between molecular and heterogeneous catalyst behavior. Once the microscopic origins of site-dependent reactivity are captured by suitable descriptors, this mechanistic understanding can inform materials screening and guide framework design toward balancing reaction energetics and accessibility.
Source: ChemRxiv
Authors: Chenxi Li, Mårten S. G. Ahlquist
Institution: KTH Royal Institute of Technology
Language: English
Field: Energy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7211944867