ACS Catalysis 最新文献

We describe a titanocene-catalyzed hydrosilylation of oxetanes to yield primary alcohols in high yields, under robust conditions and with low catalyst loading, via ET from the catalyst to the oxetane and ensuing highly efficient HAT to the radical formed from the Ti–H bond. PhSiH₃ or the inexpensive industrial waste product polymethylhydrosiloxane (PMHS) can be used as terminal reductant. The reactions are more selective and proceed under more efficient reaction conditions than titanocene-catalyzed epoxide hydrosilylations. The reasons for the high selectivity are outlined with the aid of DFT calculations and are compared with the reactions of epoxides.

Conformationally inflexible medium-sized azacycles may be stable chiral molecules even when lacking conventional chiral elements, offering significant potential applications in chiral recognition and asymmetric synthesis. Herein, an efficient kinetic resolution of inherently chiral 10-vinyltribenzo[b,d,f]azocines through chiral phosphoric-acid-catalyzed (CPA) asymmetric transfer hydrogenation of the pending alkenyl moiety has been developed. Although the chirality in the hydrogenated products, 10-alkyltribenzo[b,d,f]azocines, is acid-labile, the recovered enantioenriched 10-vinyltribenzo[b,d,f]azocines are optically stable under both acidic and thermal conditions. This approach features mild reaction conditions, good functional group tolerance, good yields, and high enantioselectivity (up to 99% ee). Density functional theory (DFT) calculations reveal the reason for optical lability of the hydrogenated products in acid.

Among the proposed mechanisms of the electrocatalytic CO₂ reduction reaction (eCO₂RR) to convert CO₂ into valuable C₂ chemicals and fuels, *CO–*CO coupling is a key C–C bond formation step. However, static density functional theory (DFT) calculations often struggle to accurately describe this process at the liquid–solid interface. In this work, we employed ab initio molecular dynamics with umbrella sampling to calculate the free energy changes of *CO–*CO coupling on Cu(111) in the presence of water. Through detailed and rigorous analysis, the bridge/hollow–bridge/hollow (*OC–CO) configuration was identified as the most favorable transition state structure at the interface, offering valuable insight into ongoing debates over the true nature of reaction sites. This preference is supported by a larger orbital-overlap integral between *C 2p and Cu 3d orbitals and enhanced charge transfer from *OC–CO to the surface. Importantly, we demonstrate that the *CO–*CO coupling barrier, despite being a thermally driven (non-electrochemical) step, is sensitive to electrode potential. A barrier reduction of ∼0.11 eV per 1.0 V negative shift was observed, potentially enhancing reaction rates by an order of magnitude. These findings underscore the dynamic nature of interfacial environments and highlight the need to reconsider the interplay between electrochemical and thermally driven steps in the eCO₂RR under varying electrode potentials.

Atomically dispersed non-noble metal–nitrogen-carbon electrocatalysts could derive a four-electron oxygen reduction reaction (ORR) described via a typical adsorbate evolution mechanism (AEM), but their kinetics are limited by the linear scaling relationship (LSR) between the *OOH and *OH. Herein, we reported heteronuclear dual-site FeN₆–CoN₄ materials obtained via integrating Fe³⁺ and Co²⁺ into pyrrole-functionalized g-C₃N₄ nanosheets. Such electrocatalysts broke the conventional LSR through a shifted oxygen dissociation mechanism (ODM: *O₂ → *O + *OH → 2 *OH). Density functional theory calculations confirmed the strongest and weakest adsorption strengths of key ORR intermediates in the CoN₄ and FeN₆ sites with a conventional AEM pathway. Under the synergistic effect of dual-site strong-weak adsorption, FeN₆–CoN₄ switched from ORR pathways to the ODM observed via in situ infrared spectroscopy for the rate-determining step (*O₂ → *O + *OH) with the decreased overpotentials of 0.41 V (FeN₆) and 0.50 V (CoN₄), enhancing intrinsic ORR kinetics. A Zn–air battery based on FeN₆–CoN₄ demonstrated an open-circuit voltage of 1.65 V approaching the theoretical 1.68 V, high-power density of 314 mW cm^–2, and durable discharge at 500 mA cm^–2. This work provides fundamental insights into dual-site synergy for regulating ORR pathways, offering a strategy for designing efficient atomic catalysts.

Hydrogen is a high-density and clean energy source, and ammonia is a hydrogen carrier. Catalytic ammonia decomposition (AD), as a means of hydrogen generation, has received much attention. High-entropy alloy (HEA) has been studied as a promising catalyst for AD. Despite many studies, the reaction network and mechanism of AD on HEA surfaces are still not well understood. Herein, we combine density functional theory calculations with microkinetic modeling to investigate the network of the AD process, including both dehydrogenation and N-containing species coupling on the two sites (site 1 and site 2), which refer to small areas centered on the two most favorable positions for NH₃ adsorption at the (111) surface of CoIrNiRhRu HEA, a catalyst showing good performance for AD at high temperatures experimentally. It is found that site 2 is much less active than site 1. On site 1, the adsorption energy of atomic N is the catalytic activity descriptor, with the rate-controlling step being N* + N* = N₂* + * and the dominant pathway being NH₃* → NH₂* → NH* → N*→ N₂*. N₂ is selectively produced on both sites beyond 700 K. The (111) surface of CoIrNiRhRu HEA has many different sites that are composed of different element combinations and feature different adsorption and kinetic properties. Linear Ridge Regression (RR) machine learning models were constructed to correlate well the site composition with the N1 species’ adsorption energies. Analysis indicates that the impact of an element on the adsorption energy and reaction kinetics can be both positive and negative depending on the position. Transition state scaling (TSS) relations were also established for the dehydrogenation and coupling reactions, and their extensibility, as well as that of the Ridge Regression models, was tested. A more active site or local structure on the CoIrNiRhRu HEA (111) surface was designed based on the RR models and the TSS relations. The activity of this designed site is 71(3840) times as high as that of site 1(site 2) at 773 K. The present paper not only presents a comprehensive understanding of AD on CoIrNiRhRu HEA surfaces but also provides a theoretical scheme to optimize and design low-temperature, highly active HEA catalysts for AD reaction, which deserves generalization for solving similar problems.

β-Galactosidases catalyze the transgalactosylation of lactose to produce prebiotic galacto-oligosaccharides (GOS), key fortificants in infant formulas. A β-galactosidase from the infant isolate Bifidobacterium breve DSM20213 (Bbreβgal-III), which belongs to the glycoside hydrolase (GH) family 42, exhibits limited transgalactosylation activity, resulting in a low yield of GOS with the predominant formation of β-(1→6)-linked GOS. Structural analysis revealed a hydrophobic-rich active site and the presence of a water tunnel connecting the deeply buried active site to the exterior environment. The highly conserved hydrophilic Arg121 residue, which is adjacent to the catalytic acid/base residue Glu160, was found to play a crucial role in the hydrolytic activity of Bbreβgal-III. The guanidino group of the Arg121 side chain forms a network of hydrogen bonds involving the catalytic Glu160 and a water molecule in the water tunnel. This influences the coordination environment of the active site, resulting in a preference for hydrolysis over transgalactosylation in Bbreβgal-III. Site-saturation mutagenesis at Arg121 revealed that all variants enhanced the transgalactosylation activity. Among these, Bbreβgal-III-R121C exhibited the highest GOS yield, reaching 34% mass of total sugars in the transgalactosylation reaction compared to 17% by the wild-type enzyme. Bbreβgal-III-R121C not only enhanced transgalactosylation but also displayed distinct changes in the main GOS components synthesized, including a shift from 6′-galactosyllactose, which is formed predominantly by wild-type Bbreβgal-III, to 3′-galactosyllactose and a notable increase in the formation of β-(1→2)-linked GOS. These results suggest that Arg121 acts as a key switch for transgalactosylation/hydrolysis activity in GH42 β-galactosidases. Furthermore, water tunnel engineering, i.e., modification of the active-site access pathway, using alanine scanning also increased the transgalactosylation activity. Disrupting the movement of water molecules within the tunnel resulted in higher transgalactosylation activity. Understanding the catalytic importance of amino acids involved in transgalactosylation and rational mutagenesis of active-site residues provided further insights into the structure−function relationships of β-galactosidases within the GH42 family.