The synthesis of macrocycles is severely impeded by concomitant oligomer formation. Here, we present a biomimetic approach that utilizes spatial confinement to increase macrocyclization selectivity in the ring clos-ing metathesis of various dienes at elevated substrate concentration up to 25 mM using an olefin me-tathesis catalyst selectively immobilized inside ordered mesoporous silicas with defined pore diameters. By this ap-proach, the ratio between macro(mono)cyclization (MMC) product and all undesired oligomerization prod-ucts (O) resulting from acyclic diene metathesis polymerization was increased from 0.55, corresponding to 35% MMC product obtained with the homogeneous catalyst, up to 1.49, corresponding to 60% MMC prod-uct. A correlation between the MMC/O ratio and the substrate-to-pore-size ratio was successfully established. Modification of the inner pore surface with dimethyldimethoxysilane allowed to fine-tune the effective pore size and to reverse surface polarity, which resulted in a further increase of the MMC/O ratio up to 2.2, corre-sponding to > 68% MMC product. Molecular-level simulations in model pore geometries help to rationalize the complex interplay between spatial confinement, specific (substrate and product) interaction with the pore surface, and diffusive transport. These effects can be synergistically adjusted for optimum selectivity by suita-ble surface modification.

The active site in ethene oligomerization catalyzed by Ni-zeolites is proposed to be a mobile Ni(II) complex, based on density functional theory-based molecular dynamics (DFT-MD) simulations corroborated by continuous-flow experiments on Ni-SSZ-24 zeolite. The results of the simulations at operating conditions show that ethene molecules reversibly mobilize the active site as they exchange with the zeolite as ligands on Ni during reaction. Microkinetic modeling was conducted on the basis of free-energy profiles derived with DFT-MD for oligomerization on these mobile [(ethene)₂-Ni-alkyl]⁺ species. The model reproduces the experimentally observed high selectivity to dimerization and indicates that the mechanism is consistent with the observed second-order rate dependence on ethene pressure.

This contribution clarifies the overoxidation‐preventing key step in the methane‐to‐methanol (MTM) conversion over copper mordenite zeolites. We followed the methane‐to‐methanol conversion over copper mordenite zeolites by NMR spectroscopy supported by DRIFTS to show that surface methoxy groups (SMGs) located at zeolite Brønsted sites are the key intermediates. The SMGs with chemical shift of 59 ppm are identical to those formed on a copper‐free reference zeolite after reaction with methanol and react with water, methanol, or carbon monoxide to yield methanol, dimethyl ether, and acetate. This reactivity corroborates the location of SMGs at Brønsted sites. We find no evidence for stable SMGs directly at copper sites and explain mechanistically why H‐form mordenites outperform their Na‐form analogues. This finding is of interest for any future process that tries to trap the intermediate methane oxidation product towards methanol.

The characteristic structural features and key interaction sites of zeolites, which govern the adsorption and diffusion behaviors of guest molecules, along with the integration of mathematical mechanisms and characterization methods, are shown.