Design, Synthesis, and Evaluation of Metal-Organic Framework Catalysts for CO2 Reduction

Thesis Abstract

Global energy demand and climate imperatives demand efficient carbon dioxide conversion strategies, yet practical catalysts that operate under mild conditions with high selectivity remain elusive. This study addresses the gap by designing, synthesizing, and evaluating a library of metal–organic framework (MOF) catalysts tailored for CO2 electroreduction and photoreduction, aiming to achieve high Faradaic efficiency, reduced overpotential, and robust long-term stability. The objective is to develop MOF-based catalysts that combine active metal centers (Fe, Cu, Co) with redox-active ligands and hierarchical porosity to enhance CO2 adsorption and electron transfer to CO2-derived products; to optimize synthesis protocols for reproducible framework quality; and to comprehensively evaluate catalytic performance under electrochemical and photochemical conditions, linking structure–property–activity relationships to mechanism. The research adopts a design–synthesis–evaluation paradigm. A modular MOF synthesis approach is employed to construct a series of isostructural frameworks with controlled metal nodes, linker functionalities, and pore environments. The population comprises synthesized MOFs (n=18) characterized by powder and single-crystal X-ray diffraction, thermogravimetric analysis, BET surface area measurements, CO2 adsorption isotherms, and X-ray photoelectron spectroscopy to confirm oxidation states and local environments. Catalytic testing uses three standardized setups (i) a gas-fed flow electrochemical cell under potentiostatic operation with 0.5 M KHCO3 electrolyte, (ii) a parallel-plate photoelectrocatalytic cell illuminated with AM 1.5G solar simulators, and (iii) in situ spectroelectrochemical measurements. Data collection instruments include operando infrared and Raman spectroscopy for intermediate detection, online gas chromatography–mass spectrometry (GC-MS) for product quantification, and high-performance liquid chromatography for liquid-phase products. Quantum-chemical calculations (density functional theory with the B3LYP-D3 functional) are integrated to model CO2 adsorption geometries and reaction barriers on representative MOF active sites, providing insight into the observed activity trends. The methodological framework combines experimental design with statistical analysis to establish robust structure–property–performance correlations. Descriptive statistics summarize synthesis reproducibility and catalyst porosity metrics. Multivariate regression models and analysis of variance (ANOVA) assess the influence of metal identity, linker substituents, and pore engineering on Faradaic efficiency for CO and formate, overpotential, and current density. Kinetic analyses extract Tafel slopes and turnover frequencies to compare catalytic performance, while operando spectroscopic data support a reaction mechanism consistent with a b3-type electron transfer process and coordinated CO2 activation at open metal sites. The study also applies a theoretical framework drawing on the Sabatier principle and molecular catalyst design concepts to rationalize observed selectivity trends. Expected findings indicate that MOFs incorporating high-spin Fe or Cu centers with electron-rich azolate linkers and hierarchical porosity exhibit reduced overpotentials and enhanced CO2-to-CO selectivity (>70% FE_CO at ?0.8 V vs RHE) compared with control MOFs lacking redox-active ligands. It is anticipated that operando spectroscopy will reveal key intermediates such as CO2–MOF adducts and COOH* species, supporting a coupled electron–proton transfer mechanism. The study expects to observe catalyst stability over 50 hours of continuous operation with minimal loss in Faradaic efficiency, attributable to framework robustness and self-healing porosity. The contribution to knowledge includes (i) a validated design strategy for MOF catalysts that couples redox-active ligands with tunable pore environments to optimize CO2 reduction, (ii) a comprehensive performance map linking metal identity, linker functionality, and porosity to activity and selectivity, and (iii) mechanistic insight into CO2 activation within MOF matrices supported by in situ characterization and quantum-chemical modeling. Practical implications extend to scalable MOF-based electrocatalysts and photogenerated catalysts for CO2 utilization. The study concludes that carefully engineered MOFs can rival traditional molecular catalysts in efficiency and selectivity while offering superior stability, with recommendations emphasizing further exploration of post-synthetic modification and in situ operando diagnostics to refine activity and durability.