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Rising anthropogenic carbon emissions have dire environmental consequences, necessitating remediative approaches, which includes use of solid sorbents. Here, aminopolymers (poly(ethylene imine) (PEI) and poly(propylene imine) (PPI)) are supported within solid mesoporous MIL‐101(Cr) to examine effects of support defect density on aminopolymer‐MOF interactions for CO₂uptake and stability during uptake‐regeneration cycles. Using simulated flue gas (10 % CO₂in He), MIL‐101(Cr)‐ρ_high(higher defect density) shows 33 % higher uptake capacity per gram adsorbent than MIL‐101(Cr)‐ρ_low(lower defect density) at 308 K, consistent with increased availability of undercoordinated Cr adsorption sites at missing linker defects. Increasing aminopolymer weight loadings (10–50 wt.%) within MIL‐101(Cr)‐ρ_lowand MIL‐101(Cr)‐ρ_highincreases amine efficiencies and CO₂uptake capacities relative to bare MOFs, though both incur CO₂diffusion limitations through confined, viscous polymer phases at higher (40–50 wt.%) loadings. Benchmarked against SBA‐15, lower polymer packing densities (PPI>PEI), weaker and less abundant van der Waals interactions between aminopolymers and pore walls, and open framework topology increase amine efficiencies. Interactions between amines and Cr defect sites incur amine efficiency losses but grant higher thermal and oxidative stability during uptake‐regeneration cycling. Finally, >25 % higher CO₂uptake capacities are achieved for aminopolymer/MIL‐101(Cr)‐ρ_highunder humid conditions, demonstrating promise for realistic applications.

 

Isostructural Cr and Fe nanoporous MIL-101, synthesized without mineralizing agents, are investigated for styrene oxidation utilizing aqueous hydrogen peroxide to yield valuable oxygenates for chemical synthesis applications. Styrene conversion rates and oxygenate product distributions both depend on metal identity, as MIL-101(Fe) is more reactive for total styrene oxidation and is more pathway selective, preferring aldehyde (benzaldehyde) formation at the α-carbon to the aromatic ring, where MIL-101(Cr) sustains epoxide (styrene oxide) production at the same α-carbon. These pathways often involve hydrogen peroxide derived radical intermediates (O, –HOO˙, –HO − ˙) and metallocycle transition states. We postulate that the higher reactivity of one of these surface intermediates, Fe( iv )O relative to Cr( iv )O, leads to higher styrene oxidation rates for MIL-101(Fe), while higher electrophilicity of Cr( iii )–OOH intermediates translates to the higher styrene oxide selectivity observed for MIL-101(Cr). Secondary styrene oxide and benzaldehyde conversions are observed over both analogs, but the former is more prevalent over MIL-101(Fe) due to higher Lewis/Brønsted acid site density and strength compared to MIL-101(Cr). Recyclability experiments combined with characterization via XRD, SEM/EDXS, and FT-IR and UV-vis spectroscopies show that the nature of MIL-101(Fe) sites does not change significantly with each cycle, whereas MIL-101(Cr) suffers from metal leaching, which impacts styrene conversion rates and product distribution. Both catalysts require active site regeneration, though MIL-101(Fe) sites are more susceptible to reactivation, even under mild conditions. Finally, examination of styrene conversion for three unique synthesized phases of MIL-101(Cr) rationalizes that nodal defects are largely responsible for observed reactivity and selectivity but predispose the framework to metal leaching as a predominant deactivation mechanism.