Oxidation of ethane to ethanol by N2O in a metal-organic framework with coordinatively unsaturated iron(II) sites

Hierarchical porous metal–organic gels and derived materials: from fundamentals to potential applications

This review summarizes recent progress in the development and applications of metal–organic gels (MOGs) and their hybrids and derivatives dividing them into subclasses and discussing their synthesis, design and structure–property relationship.

Light alkane oxidation over well-defined active sites in metal–organic framework materials

We review structure–catalytic property relationships for MOF materials used in the direct oxidation of light alkanes, focusing specifically on the elucidation of active site structures and probes for reaction mechanisms.

Catalytic properties of the ferryl ion in the solid state: a computational review

This review summarises the last findings in the emerging field of heterogeneous catalytic oxidation of light alkanes by ferryl species supported on solid-state systems such as the conversion of methane into methanol by FeO-MOF74.

N-Formylation of amines utilizing CO2 by a heterogeneous metal–organic framework supported single-site cobalt catalyst

Single-site cobalt-hydride supported on oxo-nodes of a porous aluminium metal–organic framework is a chemoselective and reusable catalyst for N-formylation of amines using CO2.

Metal–organic framework (MOF)-, covalent-organic framework (COF)-, and porous-organic polymers (POP)-catalyzed selective C–H bond activation and functionalization reactions

The review summarizes the state-of-the-art of C–H active transformations over crystalline and amorphous porous materials as new emerging heterogeneous (photo)catalysts.

Chemoselective and Tandem Reduction of Arenes Using a Metal-Organic Framework-Supported Single-Site Cobalt Catalyst

The development of heterogeneous, chemoselective, and tandem catalytic systems using abundant metals is vital for the sustainable synthesis of fine and commodity chemicals. We report a robust and recyclable single-site cobalt-hydride catalyst based on a porous aluminum metal-organic framework (DUT-5 MOF) for chemoselective hydrogenation of arenes. The DUT-5 node-supported cobalt(II) hydride (DUT-5-CoH) is a versatile solid catalyst for chemoselective hydrogenation of a range of nonpolar and polar arenes, including heteroarenes such as pyridines, quinolines, isoquinolines, indoles, and furans to afford cycloalkanes and saturated heterocycles in excellent yields. DUT-5-CoH exhibited excellent functional group tolerance and could be reusable at least five times without decreased activity. The same MOF-Co catalyst was also efficient for tandem hydrogenation-hydrodeoxygenation of aryl carbonyl compounds, including biomass-derived platform molecules such as furfural and hydroxymethylfurfural to cycloalkanes. In the case of hydrogenation of cumene, our spectroscopic, kinetic, and density functional theory (DFT) studies suggest the insertion of a trisubstituted alkene intermediate into the Co-H bond occurring in the turnover limiting step. Our work highlights the potential of MOF-supported single-site base-metal catalysts for sustainable and environment-friendly industrial production of chemicals and biofuels.

A Reactive, Photogenerated High-Spin (S = 2) FeIV(O) Complex via O2 Activation

Addition of dioxygen at low temperature to the non-heme ferrous complex Fe^II(Me₃TACN)((OSi^Ph2)₂O) (1) in 2-MeTHF produces a peroxo-bridged diferric complex Fe₂^III(μ-O₂)(Me₃TACN)₂((OSi^Ph2)₂O)₂ (2), which was characterized by UV-vis, resonance Raman, and variable field Mössbauer spectroscopies. Illumination of a frozen solution of 2 in THF with white light leads to homolytic O-O bond cleavage and generation of a Fe^IV(O) complex 4 (ν(Fe=O) = 818 cm^-1; δ = 0.22 mm s^-1, ΔE_Q = 0.23 mm s^-1). Variable field Mössbauer spectroscopy measurements show that 4 is a rare example of a high-spin S = 2 Fe^IV(O) complex and the first synthetic example to be generated directly from O₂. Complex 4 is highly reactive, as expected for a high-spin ferryl, and decays rapidly in fluid solution at cryogenic temperatures. This decay process in 2-MeTHF involves C-H cleavage of the solvent. However, the controlled photolysis of 2 in situ with visible light and excess phenol substrate leads to competitive phenol oxidation, via the proposed transient generation of 4 as the active oxidant.

A new cotton functionalized with iron(III) trimer-like metal framework as an effective strategy for the adsorption of triarylmethane dye: An insight into the dye adsorption processes

A new Cotton@Fe-BTC composite formed by Fe-BTC (BTC-H3: trimesic acid) metal framework (Fe-BTC MOF loading as high 38 wt %) supported by cellulose fiber is synthesized in aqueous media using a simple and green preparation method, described for the first time in this manuscript. This new strategy relies on the synergetic effect of the pure cellulose and MOFs frameworks resulting in hybrid nanofibers of MOFs@cellulose composite. A complete characterization of the composite material reveals its structural similarity to MIL-100(Fe), a Fe-BTC material. The Cotton@Fe-BTC composite potential use as an eco-friendly and low-cost adsorbent was evaluated for its adsorptive performance for the removal of dye belonging to the triarylmethane dye family (Malachite Green (MQ), Brilliant Green (BG), Pararosaniline (PR), Basic Fuchsine (BF), Crystal Violet (CV), Methyl Green (Met-G), Victoria Blue B (VB), Acid Fuchsin (AF) and Aniline Blue (AB)) in aqueous solution. The fast kinetics and high dye removal efficiencies (>90%) obtained in aqueous solutions. The structure of Cotton@Fe-BTC network, contributed to the remarkable adsorption properties towards a variety of triphenylmethanedye. The interparticle studies showed two main steps in the dye adsorption processes, with the exception of AF and BG. The equilibrium adsorption capacities qe (mg/g) follow the order: AF (3.64) Collapse

Key Words

• Adsorption
• Fe-BTC
• Natural cotton
• Solvation/desolvation penalty processes
• Triphenylmetane dye
• Water

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MESH Headings Collapse

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Affiliation(s)

J.E. Conde-González Departamento de Química, Unidad Departamental de Química Analítica, Facultad de Ciencias, Universidad de La Laguna, Tenerife, Spain
P. Lorenzo-Luis Inorganic Chemistry Area, Section of Chemistry Faculty of Science, Tenerife, Spain Instituto Universitario de Bio-Orgánica “Antonio González”, University of La Laguna, Tenerife, Spain
V. Salvadó Department de Química, Facultat de Ciències, Universitat de Girona, C/ M Aurèlia Capmany, 69, 17003 Girona, Spain
J. Havel Department of Chemistry, Faculty of Science, Masaryk University, Kamenice 5/A14, 625 00 Brno, Czech Republic
E.M. Peña-Méndez Departamento de Química, Unidad Departamental de Química Analítica, Facultad de Ciencias, Universidad de La Laguna, Tenerife, Spain

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Using Machine Learning and Data Mining to Leverage Community Knowledge for the Engineering of Stable Metal-Organic Frameworks

Although the tailored metal active sites and porous architectures of MOFs hold great promise for engineering challenges ranging from gas separations to catalysis, a lack of understanding of how to improve their stability limits their use in practice. To overcome this limitation, we extract thousands of published reports of the key aspects of MOF stability necessary for their practical application: the ability to withstand high temperatures without degrading and the capacity to be activated by removal of solvent molecules. From nearly 4000 manuscripts, we use natural language processing and image analysis to obtain over 2000 solvent-removal stability measures and 3000 thermal degradation temperatures. We analyze the relationships between stability properties and the chemical and geometric structures in this set to identify limits of prior heuristics derived from smaller sets of MOFs. By training predictive machine learning (ML, i.e., Gaussian process and artificial neural network) models to encode the structure-property relationships with graph- and pore-structure-based representations, we are able to make predictions of stability orders of magnitude faster than conventional physics-based modeling or experiment. Interpretation of important features in ML models provides insights that we use to identify strategies to engineer increased stability into typically unstable 3d-transition-metal-containing MOFs that are frequently targeted for catalytic applications. We expect our approach to accelerate the time to discovery of stable, practical MOF materials for a wide range of applications.

From Molecules to Frameworks to Superframework Crystals

Building chemical structures of complexity and functionality approaching the level of biological systems is an ongoing challenge. A general synthetic strategy is proposed by which progressive levels of complexity are achieved through the building block approach whereby molecularly defined constructs at one level serve as constituent units of the next level, all being linked through strong bonds-"augmented reticular chemistry". Specifically, current knowledge of linking metal complexes and organic molecules into reticular frameworks is applied here to linking the crystals of these frameworks into supercrystals (superframeworks). This strategy allows for the molecular control exercised on the molecular regime to be translated into higher augmentation levels to produce systems capable of dynamics and complex functionality far exceeding current materials.

Rapid mechanochemical synthesis of metal-organic frameworks using exogenous organic base

Metal-organic frameworks (MOFs) bearing coordinatively unsaturated metal centers, exemplified by the MOF-74 family of frameworks, are promising for applications ranging from gas separations and storage to Lewis acid catalysis. However, the scalable synthesis of MOF-74 analogues remains a significant challenge. Recently, mechanochemistry has emerged as a sustainable strategy for the preparation of MOFs in the solid state with minimal solvent waste. Mechanochemical methods typically rely on metal salts bearing basic anions to deprotonate the conjugate acid of the organic linker and a small amount of organic solvent or water to facilitate liquid assisted grinding. Here, we demonstrate that the liquid exogenous organic base Hünig's base (N,N-diisopropylethylamine) can fulfill both roles, enabling the mechanochemical synthesis of M2(dobdc) analogues (M = Mg, Mn, Co, Ni, Cu, Zn; dobdc4- = 2,5-dioxidobenzene-1,4-dicarboxylate) using metal nitrate salts in only 5 minutes at room temperature. Importantly, we demonstrate that this straightforward method can be generalized to prepare the isomeric framework Mg2(m-dobdc) (m-dobdc4- = 2,4-dioxidobenzene-1,5-dicarboxylate) and the expanded framework Mg2(dobpdc) (dobpdc4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) under solvent-free conditions for the first time. The MOFs prepared using this method possess high crystallinities and surface areas, with the Mg2(m-dobdc) prepared herein representing the first reported permanently porous variant of this framework. This new sustainable mechanochemical synthesis of MOF-74 analogues should enable their preparation on a large scale for industrial applications.

Tunable Band Gaps in MUV-10(M): A Family of Photoredox-Active MOFs with Earth-Abundant Open Metal Sites

Titanium-based metal-organic frameworks (Ti-MOFs) have attracted intense research attention because they can store charges in the form of Ti³⁺ and they serve as photosensitizers to cocatalysts through heterogeneous photoredox reactions at the MOF-liquid interface. Both the charge storage and charge transfer depend on the redox potentials of the MOF and the molecular substrate, but the factors controlling these energetic aspects are not well understood. Additionally, photocatalysis involving Ti-MOFs relies on cocatalysts rather than the intrinsic Ti reactivity, in part because Ti-MOFs with open metal sites are rare. Here, we report that the class of Ti-MOFs known as MUV-10 can be synthetically modified to include a range of redox-inactive ions with flexible coordination environments that control the energies of the photoactive orbitals. Lewis acidic cations installed in the MOF cluster (Cd²⁺, Sr²⁺, and Ba²⁺) or introduced to the pores (H⁺, Li⁺, Na⁺, K⁺) tune the electronic structure and band gaps of the MOFs. Through the use of optical redox indicators, we report the first direct measurement of the Fermi levels (redox potentials) of photoexcited MOFs in situ. Taken together, these results explain the ability of Ti-MOFs to store charges and provide design principles for achieving heterogeneous photoredox chemistry with electrostatic control.

Beyond Radical Rebound: Methane Oxidation to Methanol Catalyzed by Iron Species in Metal-Organic Framework Nodes

Recent work has exploited the ability of metal-organic frameworks (MOFs) to isolate Fe sites that mimic the structures of sites in enzymes that catalyze selective oxidations at low temperatures, opening new pathways for the valorization of underutilized feedstocks such as methane. Questions remain as to whether the radical-rebound mechanism commonly invoked in enzymatic and homogeneous systems also applies in these rigid-framework materials, in which resisting the overoxidation of desired products is a major challenge. We demonstrate that MOFs bearing Fe(II) sites within Fe₃-μ₃-oxo nodes active for conversion of CH₄ + N₂O mixtures (368-408 K) require steps beyond the radical-rebound mechanism to protect the desired CH₃OH product. Infrared spectra and density functional theory show that CH₃OH_(g) is stabilized as Fe(III)-OCH₃ groups on the MOF via hydrogen atom transfer with Fe(III)-OH groups, eliminating water. Consequently, upon addition of a protonic zeolite in inter- and intrapellet mixtures with the MOF, we observed increases in CH₃OH selectivity with increasing ratio and proximity of zeolitic H⁺ to MOF-based Fe(II) sites, as methanol is protected within the zeolite. We infer from the data that CH₃OH_(g) is formed via the radical-rebound mechanism on Fe(II) sites but that subsequent transport and dehydration steps are required to protect CH₃OH_(g) from overoxidation. The results demonstrate that the radical-rebound mechanism commonly invoked in this chemistry is insufficient to explain the reactivity of these systems, that the selectivity-controlling steps involve both chemical and physical rate phenomena, as well as offering a strategy to mitigate overoxidation in these and similar systems.

Metal-Organic Framework-Confined Single-Site Base-Metal Catalyst for Chemoselective Hydrodeoxygenation of Carbonyls and Alcohols

Chemoselective deoxygenation of carbonyls and alcohols using hydrogen by heterogeneous base-metal catalysts is crucial for the sustainable production of fine chemicals and biofuels. We report an aluminum metal-organic framework (DUT-5) node support cobalt(II) hydride, which is a highly chemoselective and recyclable heterogeneous catalyst for deoxygenation of a range of aromatic and aliphatic ketones, aldehydes, and primary and secondary alcohols, including biomass-derived substrates under 1 bar H₂. The single-site cobalt catalyst (DUT-5-CoH) was easily prepared by postsynthetic metalation of the secondary building units (SBUs) of DUT-5 with CoCl₂ followed by the reaction of NaEt₃BH. X-ray photoelectron spectroscopy and X-ray absorption near-edge spectroscopy (XANES) indicated the presence of Co^II and Al^III centers in DUT-5-CoH and DUT-5-Co after catalysis. The coordination environment of the cobalt center of DUT-5-Co before and after catalysis was established by extended X-ray fine structure spectroscopy (EXAFS) and density functional theory. The kinetic and computational data suggest reversible carbonyl coordination to cobalt preceding the turnover-limiting step, which involves 1,2-insertion of the coordinated carbonyl into the cobalt-hydride bond. The unique coordination environment of the cobalt ion ligated by oxo-nodes within the porous framework and the rate independency on the pressure of H₂ allow the deoxygenation reactions chemoselectively under ambient hydrogen pressure.

Catalytic Oxygenation of Hydrocarbons by Mono-μ-oxo Dicopper(II) Species Resulting from O-O Cleavage of Tetranuclear CuI /CuII Peroxo Complexes

One of the challenges of catalysis is the transformation of inert C-H bonds to useful products. Copper-containing monooxygenases play an important role in this regard. Here we show that low-temperature oxygenation of dinuclear copper(I) complexes leads to unusual tetranuclear, mixed-valent μ₄ -peroxo [Cu^I /Cu^II ]₂ complexes. These Cu₄ O₂ intermediates promote irreversible and thermally activated O-O bond homolysis, generating Cu₂ O complexes that catalyze strongly exergonic H-atom abstraction from hydrocarbons, coupled to O-transfer. The Cu₂ O species can also be produced with N₂ O, demonstrating their capability for small-molecule activation. The binding and cleavage of O₂ leading to the primary Cu₄ O₂ intermediate and the Cu₂ O complexes, respectively, is elucidated with a range of solution spectroscopic methods and mass spectrometry. The unique reactivities of these species establish an unprecedented, 100 % atom-economic scenario for the catalytic, copper-mediated monooxygenation of organic substrates, employing both O-atoms of O₂ .

Dimensional Reduction of Lewis Acidic Metal-Organic Frameworks for Multicomponent Reactions

Owing to hindered diffusions, the application of porous catalytic materials has been limited to relatively simple organic transformations with small substrates. Herein we report a dimensional reduction strategy to construct a two-dimensional metal-organic framework (MOF), Zr₆OTf-BTB, with 96% accessible Lewis acidic sites as probed by the bulky Lewis base pivalonitrile. With nearly free substrate accessibility, Zr₆OTf-BTB outperformed two three-dimensional MOF counterparts of similar Lewis acidity (Zr₆OTf-BPDC and Zr₆OTf-BTC) in catalyzing sterically hindered multicomponent reactions (MCRs) for the construction of tetrahydroquinoline and aziridine carboxylate derivatives with high turnover numbers (TONs). Zr₆OTf-BTB was also superior to the homogeneous benchmark Sc(OTf)₃ with nearly 14 times higher TON and 9 times longer catalyst lifetime. Furthermore, the topology-activity relationships in these Zr-based Lewis acidic MOFs were rationalized by comparing their Lewis acidity, numbers of Lewis acidic sites, and sterically accessible Lewis acidic sites. Zr₆OTf-BTB was successfully used to construct several bioactive molecules via MCRs with excellent efficiency. This dimensional reduction strategy should allow the development of other MOF catalysts for synthetically useful and complicated organic transformations.

In crystallo organometallic chemistry

X-ray crystallography is an invaluable tool in design and development of organometallic catalysis, but application typically requires species to display sufficiently high solution concentrations and lifetimes for single crystalline samples to be obtained. In crystallo organometallic chemistry relies on chemical reactions that proceed within the single-crystal environment to access crystalline samples of reactive organometallic fragments that are unavailable by alternate means. This highlight describes approaches to in crystallo organometallic chemistry including (a) solid-gas reactions between transition metal complexes in molecular crystals and diffusing small molecules, (b) reactions of organometallic complexes within the extended lattices of metal-organic frameworks (MOFs), and (c) intracrystalline photochemical transformations to generate reactive organometallic fragments. Application of these methods has enabled characterization of catalytically important transient species, including σ-alkane adducts of transition metals, metal alkyl intermediates implicated in metal-catalyzed carbonylations, and reactive M-L multiply bonded species involved in C-H functionalization chemistry. Opportunities and challenges for in crystallo organometallic chemistry are discussed.

Evaluating the Robustness of Metal-Organic Frameworks for Synthetic Chemistry

Metal-organic frameworks (MOFs) are emerging as sustainable reagents and catalysts with promising applications in synthetic chemistry. Although the hydrothermal stabilities of MOFs have been well studied, their robustness toward various reagents, including acids, bases, nucleophiles, electrophiles, oxidants, and reductants, remains poorly characterized. As such, heterogeneous platforms for promising catalysts are generally identified on an ad hoc basis and have largely been limited to carboxylate frameworks to date. To address these limitations, here we systematically characterize the robustness of 17 representative carboxylate, salicylate, and azolate MOFs toward 30 conditions representing the scope of synthetic organic chemistry. Specifically, analysis of the full width at half-maximum of powder X-ray diffraction patterns, as well as infrared spectroscopy, 77 K N2 adsorption measurements, and scanning electron microscopy in select cases are employed to appraise framework degradation and dissolution under a range of representative conditions. Our studies demonstrate that azolate MOFs, such as Fe2(bdp)3 (bdp2- = 4,4'-(1,4-phenylene)bis(pyrazolate)), generally possess excellent chemical stabilities under myriad conditions. In addition, we find that carboxylate and salicylate frameworks possess complementary stabilities, with carboxylate MOFs possessing superior robustness toward acids, electrophiles, and oxidants, and salicylate MOFs demonstrating improved robustness toward bases, nucleophiles, and reductants. The guidelines provided herein should facilitate the rational design of robust frameworks for applications in synthetic chemistry and guide the development of new strategies for the postsynthetic modification of MOFs as well.

Metal–Organic Frameworks as Versatile Platforms for Organometallic Chemistry

Metal–organic frameworks (MOFs) are emerging porous materials with highly tunable structures developed in the 1990s, while organometallic chemistry is of fundamental importance for catalytic transformation in the academic and industrial world for many decades. Through the years, organometallic chemistry has been incorporated into functional MOF construction for diverse applications. Here, we will focus on how organometallic chemistry is applied in MOF design and modifications from linker-centric and metal-cluster-centric perspectives, respectively. Through structural design, MOFs can function as a tailorable platform for traditional organometallic transformations, including reaction of alkenes, cross-coupling reactions, and C–H activations. Besides, an overview will be made on other application categories of organometallic MOFs, such as gas adsorption, magnetism, quantum computing, and therapeutics.

Buffered Coordination Modulation as a Means of Controlling Crystal Morphology and Molecular Diffusion in an Anisotropic Metal-Organic Framework

Significant advances have been made in the synthesis of chemically selective environments within metal-organic frameworks, yet materials development and industrial implementation have been hindered by the inability to predictively control crystallite size and shape. One common strategy to control crystal growth is the inclusion of coordination modulators, which are molecular species designed to compete with the linker for metal coordination during synthesis. However, these modulators can simultaneously alter the pH of the reaction solution, an effect that can also significantly influence crystal morphology. Herein, noncoordinating buffers are used to independently control reaction pH during metal-organic framework synthesis, enabling direct interrogation of the role of the coordinating species on crystal growth. We demonstrate the efficacy of this strategy in the synthesis of low-dispersity single-crystals of the framework Co₂(dobdc) (dobdc^4-= 2,5-dioxido-1,4-benzenedicarboxylate) in a pH 7-buffered solution using cobalt(II) acetate as the metal source. Density functional theory calculations reveal that acetate competitively binds to Co during crystallization, and by using a series of cobalt(II) salts with carboxylate anions of varying coordination strength, it is possible to control crystal growth along the c-direction. Finally, we use zero length column chromatography to show that crystal morphology has a direct impact on guest diffusional path length for the industrially important hydrocarbon m-xylene. Together, these results provide molecular-level insight into the use of modulators in governing crystallite morphology and a powerful strategy for the control of molecular diffusion rates within metal-organic frameworks.

Spectroscopic Evidence of Hyponitrite Radical Intermediate in NO Disproportionation at a MOF-Supported Mononuclear Copper Site

Dianionic hyponitrite (N₂ O₂ ^2- ) is often proposed, based on model complexes, as the key intermediate in reductive coupling of nitric oxide to nitrous oxide at the bimetallic active sites of heme-copper oxidases and nitric oxide reductases. In this work, we examine the gas-solid reaction of nitric oxide with the metal-organic framework Cu^I -ZrTpmC* with a suite of in situ spectroscopies and density functional theory simulations, and identify an unusual chelating N₂ O₂ ^.- intermediate. These results highlight the advantage provided by site-isolation in metal-organic frameworks (MOFs) for studying important reaction intermediates, and provide a mechanistic scenario compatible with the proposed one-electron couple in these enzymes.

Bifunctional Metal-Organic Layer with Organic Dyes and Iron Centers for Synergistic Photoredox Catalysis

Here we report the design of a bifunctional metal-organic layer (MOL), Hf-EY-Fe, by bridging eosin Y (EY)-capped Hf₆ secondary building units (SBUs) with Fe-TPY (TPY = 4'-(4-carboxyphenyl)[2,2':6',2''-terpyridine]-5,5''-dicarboxylate) ligands. With the organic dye EY as an efficient photosensitizer and TPY-Fe(OTf)₂ as the catalytic center, Hf-EY-Fe efficiently catalyzes aminotrifluoromethylation, hydroxytrifluoromethylation, and chlorotrifluoromethylation of alkenes. Hf-EY-Fe also catalyzes the synthesis of CF₃-substituted derivatives of large bioactive molecules such as rotenone, estrone, and adapalene with sizes of up to 2.2 nm. The proximity between EY and iron centers and their site isolation in Hf-EY-Fe enhance catalytic activity while inhibiting their mutual deactivation, leading to high turnover numbers of up to 1840 and good recyclability of the MOL catalyst.

Shifting the scaling relations of single-atom catalysts for facile methane activation by tuning the coordination number

We investigate oxidative methane activation on a wide range of single transition metal atom catalysts embedded on N-doped graphene derivatives using density functional theory calculations. An inverse scaling relationship between *O formation and its hydrogen affinity is observed, consistent with a previous report. However, we find that the latter scaling line can be shifted towards a more reactive region by tuning the coordination number (CN) of the active metal sites. Specifically, we find that lowering the CN plays an important role in increasing the reactivity for methane activation via a radical-like transition state by moving the scaling lines. Thus, in the new design strategy suggested here, different from the conventional efforts focusing mainly on breaking the scaling relations, one maintains the scaling relations but moves them towards more reactive regions by controlling the coordination number of the active sites. With this design principle, we suggest several single atom catalysts with lower C-H activation barriers than some of the most active methane activation catalysts in the literature such as Cu-based zeolites.

Defects as catalytic sites for the oxygen evolution reaction in Earth-abundant MOF-74 revealed by DFT

The oxygen evolution reaction (OER) is the bottleneck of hydrogen production via water splitting and understanding electrocatalysts at atomic level becomes paramount to enhance the efficiency of this process.

The efficient separation of N2O/CO2 using unsaturated Fe2+ sites in MIL-100Fe

It is a big challenge to separate N2O from CO2 using adsorption because they have similar physical properties. The Fe3+-F- site in MIL-100Fe transforms to an unsaturated Fe2+ site under high-temperature activation (300 °C), and the target sorbent MIL-100Fe-300 exhibits the biggest difference in CO2 and N2O adsorption capacity, and the selectivity of N2O/CO2 (50%/50%) is up to 3.00 at 298 K. According to DFT calculations, the original Fe3+-F- site has strong interaction with CO2, but the open Fe2+ site has a stronger interaction with N2O. Through a breakthrough experiment, it was confirmed that MIL-100Fe-300 has the best N2O/CO2 separation performance, making it potentially a useful material in industry.

Mechanistic understanding of methane-to-methanol conversion on graphene-stabilized single-atom iron centers

DFT calculations and kinetic modeling elucidate solvent effects and complex mechanisms for the room-temperature methane-to-methanol conversion on an FeN4/graphene catalyst.

Status and prospects of the decentralised valorisation of natural gas into energy and energy carriers

We critically review the recent advances in process, reactor, and catalyst design that enable process miniaturisation for decentralised natural gas upgrading into electricity, liquefied natural gas, fuels and chemicals.

The role of metal–organic porous frameworks in dual catalysis

Metal–organic frameworks (MOFs) are a valuable group of porous crystalline solids with inorganic and organic parts that can be used in dual catalysis.

MOF-74-type frameworks: tunable pore environment and functionality through metal and ligand modification

This highlight demonstrates a comprehensive overview of MOF-74-type frameworks in terms of synthetic approaches and pre- or post-synthetic modification approaches.

Unveiling the catalytic potential of the Fe(iv)oxo species for the oxidation of hydrocarbons in the solid state

We have investigated the three steps in the conversion of methane into methanol by Fe(iv)Ooxo species supported in MOF-74. We use ab initio MD and static approximations to predict the reaction barriers using enthalpy ΔH and free energy ΔG.

Using anion photoelectron spectroscopy of cluster models to gain insights into mechanisms of catalyst-mediated H2 production from water

Metal oxide cluster models of catalyst materials offer a powerful platform for probing the molecular-scale features and interactions that govern catalysis. This perspective gives an overview of studies implementing the combination of anion photoelectron (PE) spectroscopy and density functional theory calculations toward exploring cluster models of metal oxides and metal-oxide supported Pt that catalytically drive the hydrogen evolution reaction (HER) or the water-gas shift reaction. The utility in the combination of these experimental and computational techniques lies in our ability to unambiguously determine electronic and molecular structures, which can then connect to results of reactivity studies. In particular, we focus on the activity of oxygen vacancies modeled by suboxide clusters, the critical mechanistic step of forming proximal metal hydride and hydroxide groups as a prerequisite for H2 production, and the structural features that lead to trapped dihydroxide groups. The pronounced asymmetric oxidation found in heterometallic group 6 oxides and near-neighbor group 5/group 6 results in higher activity toward water, while group 7/group 6 oxides form very specific stoichiometries that suggest facile regeneration. Studies on the trans-periodic combination of cerium oxide and platinum as a model for ceria supported Pt atoms and nanoparticles reveal striking negative charge accumulation by Pt, which, combined with the ionic conductivity of ceria, suggests a mechanism for the exceptionally high activity of this system towards the water-gas shift reaction.