Computational study of the carbonyl-ene reaction between formaldehyde and propylene encapsulated in coordinatively unsaturated metal-organic frameworks M3(btc)2 (M = Fe, Co, Ni, Cu and Zn)

Theoretical investigation of the carbonyl-ene reaction between encapsulated formaldehyde and propylene over M-Cu-BTC paddlewheels (M= Be, Mg, and Ca): A DFT study

Formaldehyde is a VOC gas that plays a key role in air pollution. To limit emissions into the environment, the utilization of this waste as a raw material is a promising way. In this work, the M06-L functional calculation was used to investigate the structure, electronic properties, and catalytic activity of group IIA metals (Be, Mg, and Ca) partial substitution on Cu-BTC paddlewheels for formaldehyde encapsulation and carbonyl-ene reaction with propylene. Formaldehyde is absorbed by the metal center of the paddlewheel via its oxygen atom. The adsorption of formaldehyde on the substituted metal sites increased as compared to the parent Cu-BTC which can facilitate formaldehyde to react with propylene. The adsorption free energies are predicted to be -15.1 (Be-Cu-BTC), -14.7 (Mg-Cu-BTC), and -14.5 (Ca-Cu-BTC) kcal mol-1, respectively. The substituted metal has a slight effect on the Lewis acidity of the Cu ion in the paddlewheel. The adsorption free energy of formaldehyde, similar to that found in the pristine Cu-BTC, is observed. For the carbonyl-ene reaction, the reaction is proposed via a single step involving the C-C bond formation between two reactants and one hydrogen of propylene methyl group moves to formaldehyde oxygen, simultaneously. It was found that the substituted metals do not affect the catalytic performance of the Cu center for this reaction. The activation energies for the reaction at the Cu center are in the range of 22.0-23.4 kcal mol-1, which are slightly different from Cu-BTC (21.5 kcal mol-1). Interestingly, the catalytic activity of this reaction on the substituted metal is greater than that on the Cu center. The catalytic activities are in the order Be-Cu-BTC (13.3 kcal mol-1) > Mg-Cu-BTC (15.9 kcal mol-1) > Ca-Cu-BTC (17.8 kcal mol-1). Among them, the Be site of the bimetallic Be-Cu-BTC paddlewheel is predicted as a promising candidate catalyst.

High energy density and extremely stable supercapacitors based on carbon aerogels with 100% capacitance retention up to 65,000 cycles

In terms of ideal future energy storage systems, besides the always-pursued energy/power characteristics, long-term stability is crucial for their practical application. Here, we report a facile and sustainable strategy for the scalable fabrication of carbon aerogels with three-dimensional interconnected nanofiber networks and rationally designed hierarchical porous structures, which are based on the carbonization of bacterial cellulose assisted by the soft template of Zn-1,3,5-benzenetricarboxylic acid. As binder-free electrodes, they deliver a fundamentally enhanced specific capacitance of 352 F ⋅ g^-1 at 1 A ⋅ g^-1 in a wide potential window (1.2 V, 6 M KOH) in comparison with those of bacterial cellulose-derived carbons (178 F ⋅ g^-1) and most activated carbons (usually lower than 250 F ⋅ g^-1). The as-assembled supercapacitors exhibit an ultrahigh capacitance of 297 F ⋅ g^-1 at 1 A ⋅ g^-1, remarkable energy density (14.83 Wh ⋅ kg^-1 at 0.60 kW ⋅ kg^-1), and extremely high stability, with 100% capacitance retention for up to 65,000 cycles at 6 A ⋅ g^-1, representing their superior energy storage performance when compared with that of state-of-the-art supercapacitors of commercial activated carbons and biomass-derived analogs.

Structures and mechanisms of CO2 cycloaddition with styrene oxide on bimetallic M–Cu–BTC MOFs (M = Mg, Ca, Al, and Ga): a DFT study

The Al–Cu–BTC catalyst having the strongest interaction with the SO molecule is the most promising catalyst for the conversion of CO₂ to cyclic carbonate.

Electronic Structure Modeling of Metal-Organic Frameworks

Owing to their molecular building blocks, yet highly crystalline nature, metal-organic frameworks (MOFs) sit at the interface between molecule and material. Their diverse structures and compositions enable them to be useful materials as catalysts in heterogeneous reactions, electrical conductors in energy storage and transfer applications, chromophores in photoenabled chemical transformations, and beyond. In all cases, density functional theory (DFT) and higher-level methods for electronic structure determination provide valuable quantitative information about the electronic properties that underpin the functions of these frameworks. However, there are only two general modeling approaches in conventional electronic structure software packages: those that treat materials as extended, periodic solids, and those that treat materials as discrete molecules. Each approach has features and benefits; both have been widely employed to understand the emergent chemistry that arises from the formation of the metal-organic interface. This Review canvases these approaches to date, with emphasis placed on the application of electronic structure theory to explore reactivity and electron transfer using periodic, molecular, and embedded models. This includes (i) computational chemistry considerations such as how functional, k-grid, and other model variables are selected to enable insights into MOF properties, (ii) extended solid models that treat MOFs as materials rather than molecules, (iii) the mechanics of cluster extraction and subsequent chemistry enabled by these molecular models, (iv) catalytic studies using both solids and clusters thereof, and (v) embedded, mixed-method approaches, which simulate a fraction of the material using one level of theory and the remainder of the material using another dissimilar theoretical implementation.

Dehydrogenation of ethanol to acetaldehyde with nitrous oxide over the metal-organic framework NU-1000: a density functional theory study

The conversion of ethanol to more valuable hydrocarbon compounds receives great attention in chemical industries because it could diminish the dependency on petroleum as raw material. We investigate the catalytic performance of Fe-supported MOF NU-1000 for the dehydrogenation of ethanol to acetaldehyde with nitrous oxide (N2O) by deriving the relevant reaction profiles with density functional theory calculations. In the proposed mechanism, the activation barrier of the rate-determining step is almost four times lower in the presence of N2O than without it. The supported NU-1000 framework plays also important role since it facilitates electron transfers and stabilizes all species along the reaction coordinate. When considering the catalytic activity of tetravalent metal centers (Zr, Hf and Ti) substituted into NU-1000 it is found that their activity decreases in the order Hf ≥ Zr > Ti, based on activation energies and turnover frequencies (TOF). Concerning MOF linkers, we show that the catalytic activity is not further improved by functionalizing NU-1000 with either electron-donating or electron-withdrawing organic groups.

The synergistic effect of Co/Ni in ultrathin metal–organic framework nanosheets for the prominent optimization of non-enzymatic electrochemical glucose detection

Co–Ni ultrathin metal organic framework nanosheets exhibited extremely high sensitivity, wide linear range, low detection limit and excellent selectivity as a glucose sensing electrode material.

Phenol Tautomerization Catalyzed by Acid-Base Pairs in Lewis Acidic Beta Zeolites: A Computational Study

We investigate the tautomerization of phenol catalyzed by acid-base active pair sites in Lewis acidic Beta zeolites by means of density functional calculations using the M06-L functional. An analysis of the catalytic mechanism shows that hafnium on the Beta zeolite causes the strongest absorption of phenol compared to zirconium, tin, and germanium. This can be rationalized by the highest delocalization of electron density between the Lewis site and the oxygen of phenol which can in turn be quantified by the perturbative E⁽²⁾ stabilization energy. The reaction is assumed to proceed in two steps, the phenol O-H bond dissociation and the protonation of the intermediate to form the cyclohexa-2,4-dien-1-one product. The rate determining step is the first one with a free activation energy of 26.3, 25.0, 22.1 and 22.7 kcal mol^-1 for Ge-Beta, Sn-Beta, Zr-Beta, and Hf-Beta zeolites, respectively. The turnover frequencies follow these reaction barriers. Hence, the intrinsic catalytic activity of the Lewis acidic Beta zeolites studied here is in the order of Hf-Beta≈Zr-Beta>Sn-Beta> Ge-Beta for the tautomerization of phenol.

Mechanistic insights into CO2 cycloaddition of styrene oxide on paddle-wheel metal clusters: a theoretical study

The reaction mechanisms for the CO₂ cycloaddition of styrene oxide catalyzed by M–BTC clusters have been systematically elucidated by means of the M06-L functional.