Non-oxidative coupling of methane is a promising route to obtain ethylene directly from natural gas. We synthesized siliceous [Fe]zeolites with MFI and CHA topologies and found that they display high selectivity (>90 % for MFI and >99 % for CHA) to ethylene and ethane among gas-phase products. Deactivated [Fe]zeolites can be regenerated by burning coke in air. In situ X-ray absorption spectroscopy demonstrates that the isolated Fe³⁺ centers in zeolite framework of fresh catalysts are reduced during the reaction to the active sites, including Fe²⁺ species and Fe (oxy)carbides dispersed in zeolite pores. Photoelectron photoion coincidence spectroscopy results show that methyl radicals are the reaction intermediates formed upon methane activation. Ethane is formed by methyl radical coupling, followed by its dehydrogenation to ethylene. Based on the observation of intermediates including allene, vinylacetylene, 1,3-butadiene, 2-butyne, and cyclopentadiene over [Fe]MFI, a reaction network is proposed leading to polyaromatic species. Such reaction intermediates are not observed over the small-pore [Fe]CHA, where ethylene and ethane are the only gas-phase products.

The choice of a solvent and the reaction conditions often defines the overall behavior of a homogeneous catalytic system by affecting the preferred reaction mechanism and thus the activity and selectivity of the catalytic process. Here, we explore the role of solvation in the mechanism of ketone reduction using a model representative of a bifunctional Mn-diamine catalyst through density functional theory calculations in a microsolvated environment by considering explicit solvent and fully solvated ab initio molecular dynamics simulations for the key elementary steps. Our computational analysis reveals the possibility of a Meerwein-Ponndorf-Verley (MPV) type mechanism in this system, which does not involve the participation of the N-H moiety and the formation of a transition-metal hydride species in ketone conversion. This path was not previously considered for Mn-based metal-ligand cooperative transfer hydrogenation homogeneous catalysis. The MPV mechanism is strongly facilitated by the solvent molecules present in the reaction environment and can potentially contribute to the catalytic performance of other related catalyst systems. Calculations indicate that, despite proceeding effectively in the second coordination sphere of the transition-metal center, the MPV reaction path retains the enantioselectivity preference induced by the presence of the small chiral N,N′-dimethyl-1,2-cyclohexanediamine ligand within the catalytic Mn(I) complex.

Potassium carbonate dispersed over a defective TiO₂support (K₂CO₃/TiO₂) is an efficient catalyst for benzene esterification with CO₂and CH₃OH. Density functional theory calculations reveal that this unique catalytic reactivity originates from the cooperation of the Ti³⁺/K⁺surface sites. The K₂CO₃promotor steers the stabilization of surface intermediates thus preventing catalyst deactivation.

Extraframework cations define the chemical versatility of zeolite catalysts. Addressing their structural complexity and dynamic behavior represents one of the main fundamental challenges in the field. Herein, we present a computational approach for the identification and analysis of the accessible pool of intrazeolite extraframework complexes with a Cu/MOR catalyst as an industrially important model system. We employ ab initio molecular dynamics for capturing the ensemble of reactive isomers with the [Cu3O3]2+ stoichiometry confined in the mordenite channels. The high structural diversity of the generated isomers was ensured by concentrating the kinetic energy along the low-curvature directions of the potential energy surface (PES). Geometrically distinct [Cu3O3]2+ complexes were identified via a series of clustering procedures ensuring that one structure of each local minima is retained. The proposed procedure has resulted in a set of previously unknown peroxo-complexes, which are >50 kJ/mol more stable than the recently hypothesized chair-shaped structure. Our analysis demonstrates that the most stable peroxo-containing clusters can be formed under operando conditions from molecular oxygen and the Cu3O unit, similar to that in methane monooxygenase (MMO) enzymes.

Metal-ligand cooperative properties of a bis-N-heterocyclic carbene ruthenium CNC pincer catalyst and its activity in CO₂ hydrogenation to formates were studied by DFT calculations complemented by NMR spectroscopy and kinetic measurements. The dearomatized Ru-CNC∗ pincer (1∗) is significantly more reactive toward metal-ligand cooperative activation of H₂ and CO₂ than the structurally related phosphine-based Ru-PNP complex. The enhanced reactivity of Ru-CNC∗ stems from the combination of electronic properties of this system and the reduced geometric constraints imposed onto the Ru center by the large and flexible CNC chelate. Heterolytic dissociation of H₂ by 1∗ results in the bis-hydrido complex 2 that is active in hydrogenation of CO₂. However, under commonly applied reaction conditions, the catalyst rapidly deactivates via metal-ligand cooperative paths. The transient formation of the dearomatized complex Ru-CNC∗ (1∗) in the course of the reaction leads to the irreversible cooperative activation of CO₂, resulting in the stable adduct 3 that is not catalytically competent. By an increase in the H₂/CO₂ ratio, this deactivation path can be effectively suppressed, resulting in a stable and rather high catalytic performance of Ru-CNC. (Chemical Equation Presented).