The molecular‐level structuration of two full photosystems into conjugated porous organic polymers is reported. The strategy of heterogenization gives rise to photosystems which are still fully ...active after 4 days of continuous illumination. Those materials catalyze the carbon dioxide photoreduction driven by visible light to produce up to three grams of formate per gram of catalyst. The covalent tethering of the two active sites into a single framework is shown to play a key role in the visible light activation of the catalyst. The unprecedented long‐term efficiency arises from an optimal photoinduced electron transfer from the light harvesting moiety to the catalytic site as anticipated by quantum mechanical calculations and evidenced by in situ ultrafast time‐resolved spectroscopy.
Porous organic polymers were used as photosystems to deliver a constant production rate for the CO2 to formate reduction for several days. Their photoactivation pathway is presented, including an ultrafast electronic energy transfer from the photosensitizer to the catalyst as evidenced by time‐resolved spectroscopy and quantum mechanical calculations.
A molecular catalyst Cp*Rh(4,4′‐bpydc)2+ and a molecular photosensitizer Ru(bpy)2(4,4′‐bpydc)2+ (bpydc=bipyridinedicarboxylic acid) were co‐immobilized into the highly porous metal–organic framework ...MIL‐101‐NH2(Al) upon easy postsynthetic impregnation. The Rh–Ru@MIL‐101‐NH2 composite allows the reduction of CO2 under visible light, while exhibiting remarkable selectivity with the exclusive production of formate. This Rh–Ru@MIL‐101‐NH2 solid represents the first example of MOFs functionalized with both a catalyst and a photosensitizer in a noncovalent fashion. Thanks to the coconfinement of the catalyst and photosensitizer into the cavity's nanospace, the MOF pores are used as nanoreactors and enable molecular catalysis in a heterogeneous manner.
Fix in a hole: A molecular catalyst Cp*Rh(4,4′‐bpydc)2+ and a molecular photosensitizer Ru(bpy)2(4,4′‐bpydc)2+ (bpydc=bipyridinedicarboxylic acid) were co‐immobilized into the highly porous MIL‐101‐NH2(Al)material. The Rh–Ru@MIL‐101‐NH2 composite effects the reduction of CO2 under visible light while exhibiting remarkable selectivity with the exclusive production of formate.
Zeolites are essential materials to industry due to their adsorption and catalytic properties. The best current approach to prepare a targeted zeolite still relies on trial and error's synthetic ...procedures since a rational understanding of the impact of synthesis variables on the final structures is still missing. To discern the role of a variety of organic templates, we perform simulations of the early stages of condensation of silica oligomers by combining DFT, Brønsted‐Evans‐Polanyi relationships and kinetic Monte Carlo simulations. We investigate an extended reaction path mechanism including 258 equilibrium reactions and 242 chemical species up to silica octamers, comparing the computed concentrations of Si oligomers with 29SI NMR experimental data. The effect of the templating agent is linked to the modification of the intramolecular H‐bond network in the growing oligomer, which produces higher concentration of 4‐membered ring intermediates, precursors of the key double‐four ring building blocks present on more than 39 known zeolite topologies.
DFT and kMC calculations are combined to investigate the impact of the most commonly used organic template molecules including the tetramethylamine cation (TMA+) both on the reaction energy profiles and the kinetics of formation of zeolite silica oligomers. The extended reaction path mechanism includes up to 258 equilibrium reactions. The templating agent is shown to produce higher concentration of 4‐membered ring intermediates.
Use the Force: A force field for the MIL‐53(Cr) framework was derived and validated by molecular dynamics simulations. This approach allows the “breathing” of the framework in the presence of CO2 to ...be captured and gives insight into the structural switching mechanism from a narrow‐ to a large‐pore form (see picture). This force field can be used directly in studies of many guest molecules and, with a minimum adjustment, for other MOF systems.
Abstract
The catalytic activity of multifunctional, microporous materials is directly linked to the spatial arrangement of their structural building blocks. Despite great achievements in the design ...and incorporation of isolated catalytically active metal complexes within such materials, a detailed understanding of their atomic‐level structure and the local environment of the active species remains a fundamental challenge, especially when these latter are hosted in non‐crystalline organic polymers. Here, we show that by combining computational chemistry with pair distribution function analysis,
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Xe NMR, and Dynamic Nuclear Polarization enhanced NMR spectroscopy, a very accurate description of the molecular structure and confining surroundings of a catalytically active Rh‐based organometallic complex incorporated inside the cavity of amorphous bipyridine‐based porous polymers is obtained. Small, but significant, differences in the structural properties of the polymers are highlighted depending on their backbone motifs.
Large hydrogen‐storage capacity at liquid‐nitrogen temperature is exhibited by the metal–organic framework MIL‐101. In the zeotype architecture of this porous solid (see picture) each intersection of ...the cages is occupied by a supertetrahedron formed by trimers of chromium octahedra assembled with benzene‐1,4‐dicarboxylate ligands.
Desolvated zeolitic imidazolate framework ZIF‐4(Zn) undergoes a discontinuous porous to dense phase transition on cooling through 140 K, with a 23 % contraction in unit cell volume. The structure of ...the non‐porous, low temperature phase was determined from synchrotron X‐ray powder diffraction data and its density was found to be slightly less than that of the densest ZIF phase, ZIF‐zni. The mechanism of the phase transition involves a cooperative rotation of imidazolate linkers resulting in isotropic framework contraction and pore space minimization. DFT calculations established the energy of the new structure relative to those of the room temperature phase and ZIF‐zni, while DSC measurements indicate the entropic stabilization of the porous room temperature phase at temperatures above 140 K.
ZIF‐4(Zn) undergoes a porous to non‐porous transition on cooling from the high‐temperature (HT) to low‐temperature (LT) phase. The nature of this transition is elucidated by a combined approach of structure solution from powder diffraction, DSC measurement, and DFT calculations.
An electrolyte engineering strategy was developed for CO2 reduction into formate with a model molecular catalyst, Rh(bpy)(Cp*)ClCl, by modifying the solvent (organic or aqueous), the proton source ...(H2O or acetic acid), and the electrode/solution interface with imidazolium‐ and pyrrolidinium‐based ionic liquids (ILs). Experimental and theoretical density functional theory investigations suggested that π+‐π interactions between the imidazolium‐based IL cation and the reduced bipyridine ligand of the catalyst improved the efficiency of the CO2 reduction reaction (CO2RR) by lowering the overpotential, while granting partial suppression of the hydrogen evolution reaction. This allowed tuning the selectivity towards formate, reaching for this catalyst an unprecedented faradaic efficiency (FEHCOO−) ≥90 % and energy efficiency of 66 % in acetonitrile solution. For the first time, relevant CO2 conversion to formic acid/formate was reached at low overpotential (0.28 V) using a homogeneous catalyst in acidic aqueous solution (pH=3.8). These results open up a new strategy based on electrolyte engineering for enhancing carbon balance in CO2RR.
CO2 reduction: The presence of imidazolium‐based ionic liquids in solution significantly impacts on molecular electrocatalysis selectivity and activity by favoring the CO2 reduction reaction vs. hydrogen evolution reaction in both acetonitrile and aqueous solution. The combination of electrolytes EMIMBF4 and acetic acid amplifies their individual roles by enhancing CO2 conversion to formate at very low overpotential (0.28 V) in acidic aqueous solution.
Breathtaking MOFs: DFT calculations reveal that the exceptional, thermally induced density change of the metal–organic framework MIL53(Al) is controlled by a competition between short‐ and long‐range ...interactions and entropic factors. As shown in the picture (C green, Al cyan, O red, H white), dispersive interactions between the phenyl rings are responsible for stabilizing a narrow‐pore form at low temperature. At 325–375 K, vibrational entropy causes the structure to expand markedly, permitting large volumes of light gases to be adsorbed.
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