ChemCatChem最新文献

High efficiency and selectivity of the electrocatalytic oxygen reduction reaction (ORR) requires fast proton, electron, and oxygen supply to the catalytic center. The kinetics of these processes depend largely on the preparation of the catalyst-containing electrode. Specifically, the type and amount of ionomer binders is crucial for the reaction performance. Nafion is currently the most frequently used ionic binder material enabling surface distribution of catalytic sites and fast proton transfer. Yet, the role of Nafion content for specific catalyst materials is not analyzed in depth, resulting in poor reproducibility and comparability between laboratories. In this work, we focus on the influence of Nafion content in particular regarding high surface area carbon electrodes for the ORR. The chosen carbon-based materials varied in their surface area and the amount of active oxygen, nitrogen, or iron sites, leading to different catalytic activities. The selection of Nafion content leads to differences in onset potential of up to 70 mV while currents varied about 2 mA/cm². For all electrode materials, an ideal Nafion content regarding reproducibility and performance could be identified. Based on our results we derive an estimation on how to choose the Nafion content based on the specific surface area (SSA) of the electrocatalyst.

Electrostatic interactions are essential in enzyme catalysis because they lower activation energies by stabilizing transition states and creating specialized active-site microenvironments. Introducing analogous features into molecular catalysts for CO₂ reduction reaction can stabilize key intermediates, suppress competing pathways, and enhance catalytic efficiency and selectivity. More information can be found in the Research Article by A. Aukauloo and co-workers (DOI: 10.1002/cctc.202501217). Artwork by Julien Smith.

Herein, we report a homogeneous, recyclable organocatalyst that converts a broad range of 1,2–disubstituted epoxides and CO₂ into cyclic carbonates at 25 °C and 1 bar CO₂. Rational placement convergence of four cooperative hydrogen bond donors adjacent to an ammonium–iodide nucleophile enables high catalytic activity and near perfect diastereoretention across diverse, poorly reactive 1,2–disubstituted epoxides. The catalyst is readily synthesized, metal–free, and maintains its performance over five consecutive recycles. Density functional theory (DFT) calculations reveal that dual–site H–bond pre–activation lowers every barrier along the reaction pathway and reduces the cyclization (RDS) barrier by approximately 1.4 kcal/mol relative to a less–convergent analogue, providing a clear mechanistic basis for the enhanced reactivity. This study demonstrates that cooperative, convergent H-bond design is a powerful strategy for enabling ambient-pressure organocatalytic CO₂ fixation into cyclic carbonates using highly unreactive internal epoxides, thereby offering generalizable design principles for sustainable and metal-free CO₂-utilization catalysis.

Methyltransferases (MTs) are versatile biocatalysts capable of regio-, stereo-, and enantioselective methylation of molecules, making them particularly valuable for late-stage functionalization of natural products and their analogues. To further broaden the applicability of these enzymes, it is essential to gain knowledge about their mode of catalysis and develop effective enzyme engineering and screening strategies. This, in turn, requires the development and application of robust analytical techniques, especially when dealing with large-scale screenings, such as those involved in mutagenesis campaigns. In this study, we have established the first uncoupled, continuous, fluorescence-based, high-throughput assay that serves as a close-to-universal system for activity determination of S-adenosyl-l-methionine-dependent MTs. The assay is based on proton release during the methylation, and its use is not limited to purified enzymes, but can also be applied with cell-free extracts and, in certain cases, pre-treated whole cells. To validate its applicability, activities of three distinct MTs with different substrate acceptor atoms (C, N, and O) were determined, and the results were benchmarked against HPLC analysis. Additionally, the assay's utility was demonstrated through a substrate scope screening and the determination of kinetic parameters. Finally, the Z’-factor was evaluated for two different potential enzyme setups to assess the assay's suitability for high-throughput applications.

Appropriate deposition of metal complex-based catalysts on solid carriers sometimes results in considerably higher catalytic activity than that of the metal complex alone, due to interactions between the complex and the solid. These catalysts could be a part of single-molecule catalysts (SMCs) or site-isolated molecular complex catalysts (SIMCs). Herein, we report a solid-supported metal complex catalyst for CH₄ oxidation at room temperature. Specifically, μ-nitrido-bridged iron phthalocyanine dimer deposited on conductive carbon black can oxidatively activate the chemically stable C─H bond of CH₄ with high efficiency even at 25°C in an aqueous solution containing H₂O₂ as an oxidant. Its catalytic activity for CH₄ oxidation is much higher than that of the commonly used Fenton reaction with Fe²⁺ and H₂O₂ under the same conditions. Such high catalytic oxidizing activity is attributable to the interaction between the specific surface sites of carbon black and the high-valent iron-oxo species of the catalyst molecule.

The heterogeneously catalyzed co-oligomerization of ethylene, propylene, and iso-butylene was studied focusing on the production of gasoline and kerosene. Silica-alumina catalysts were employed with and without nickel loading. Initially, the homo-oligomerization of iso-butylene was studied employing a series of catalysts and varying reaction conditions. Due to the high reactivity of iso-butylene, conversion was almost quantitative and selectivities to kerosene reached 96% while selectivities to gasoline reached 83%. Subsequently, co-oligomerization of iso-butylene with ethylene and propylene was investigated. Employing nickel-loaded silica-alumina catalysts, all olefin species can be converted, despite the very different reactivity. Selectivities to kerosene and gasoline were up to 92% and 83%, respectively. It is shown that iso-butylene can be easily separated from such olefin mixtures by oligomerization, due to its much higher reactivity compared to propylene and ethylene. A long-term run lasting for 196 h showed continuous deactivation of the catalyst regarding the conversion of ethylene and propylene, whereas conversion of iso-butylene remained close to 100%. As a result, conversion of iso-butylene dominates and molecular branching increases, as indicated by the isoindex. It is shown that the catalyst can be easily reactivated by heating and catalytic performance can be fully restored.