ChemCatChem最新文献

Electrochemical alkaline water electrolysis (AWE) is regarded as an effective method for producing high-purity hydrogen without relying on platinum group metal (PGM) as catalyst. However, the oxygen evolution reaction (OER), as the anode half-reaction, involves a four-electron transfer process with slow kinetics, which significantly reduces the overall reaction efficiency of AWE. Although highly efficient catalysts can accelerate the OER rate, the high overpotential of the anode still remains an important factor hindering AWE. Herein, ultrathin NiFe-layered double hydroxide (U-NiFe LDH) nanosheet arrays were synthesized and used as anode catalysts due to their robust structure, excellent flexibility, and effective interlayer anion compensation. Only 250 mV of overpotential was required for OER to reach a current density of 10 mA cm⁻² in 1 M KOH. Incorporating the additive ethanol into KOH electrolyte further reduces the required overpotential of AWE to 114 mV. The anode overpotential could be decreased by 130 mV at a current density of 100 mA cm⁻² in a three-electrode electrolysis system with U-NiFe LDH as the anode. This work provides a possible approach for the development of low-energy and green AWE technology for electrocatalytic hydrogen production.

Catalytic transfer hydrogenolysis (CTH) of aromatic ether bonds provides a promising strategy for sustainably converting lignin into useful chemicals. Design of innovative catalysts with high activity is the key for this route. Herein, we constructed the hexagonal boron nitride (h-BN)-supported Ru nanoparticles (Ru/h-BN) as the heterogeneous catalyst for the CTH of aromatic ether bonds. Notably, the fabricated Ru/h-BN catalyst could efficiently catalyze CTH of various types of aromatic ether bonds contained in lignin (i.e., 4-O-5, α-O-4, β-O-4, and aryl-O-CH₃) employing 2-propanol as the hydrogen resource without using extra acidic or basic additives. Besides, the Ru/h-BN catalyst demonstrated superior performance compared to commercial Ru/C. Systematic investigation revealed that electron-enriched Ru sites and the B atoms on h-BN collaboratively promoted the CTH reaction. Besides, a mechanism study indicated that the direct cleavage of aromatic ether bonds was the primary reaction pathway over Ru/h-BN.

Zinc-air batteries (ZABs) have garnered significant attention due to their high theoretical energy density, safety, and environmental sustainability. However, the slow oxygen reduction reaction (ORR) kinetics at the cathode remains a major challenge for improving ZAB performances. In this study, ABO₃-type perovskite transition metal oxides, particularly LaMnO₃, are explored as potential nonprecious metal catalysts to address these limitations. In this work, the LaMnO₃ catalyst was prepared using the sol-gel method, and oxygen vacancies were introduced through a novel carbon reduction approach using conductive carbon black as the reducing agent. The catalyst was reduced at different temperatures to optimize its ORR activity. The 500 °C-reduced sample (LMOC-500) shows the superior catalytic performances, achieving an onset potential of 0.937 V versus RHE and a half-wave potential of 0.824 V versus RHE. The optimized material also exhibited excellent stability in long-term discharge tests in ZAB applications, demonstrating its potential application as the ORR catalyst for ZABs.

A series of water-soluble arene-Ru(II) complexes, [(η⁶-p-cymene)RuCl(L)]⁺Cl^‒ ([Ru]-7 – [Ru]-12) (L = substituted bis-imidazole methane) exhibited efficient and selective methanol production from paraformaldehyde in water. The findings inferred a crucial role of the ligand in tuning the catalytic performance. A pH-dependent behavior of this series of catalysts was observed, where the amount of base was influential in methanol production from paraformaldehyde. The catalyst [Ru]-7 (L1 = 4,4′-((2-hydroxyphenyl)methylene)bis(2-ethyl-5-methyl-1H-imidazole) was the most efficient among the explored catalysts giving a turnover number (TON) of 1200 at 90 °C. A mechanistic cycle has also been proposed for the catalytic reaction based on the mass and NMR investigations including those using deuterium-labelled molecules.

The chain-walking mechanism, coupled with β-elimination reactions, establishes nickel complexes as a unique class of catalysts in olefin polymerization, giving access to a variety of polyethylene products from only ethylene monomer. In this study, a set of 8-(2,6-bis(aryl)-3,4,5-trifluorophenyl)imino-5,6,7-trihydroquinoline-nickel bromide complexes [aryl = Ph₂CH for Ni^H, (4-FPh)₂CH for Ni^F, (4-ClPh)₂CH for Ni^Cl, (4-MePh)₂CH for Ni^Me, (4-tBuPh)₂CH for Ni^tBu] was designed, prepared, and investigated for ethylene polymerization. Upon activation with MAO, these precatalysts exhibited high catalytic activity (as high as 3.1 × 10⁶ g mol⁻¹ h⁻¹) and produced polyethylene with tunable chain walking (branching degree = 58–90/1000C), chain transfer (polymer M_w = 0.7–2.8 kg mol⁻¹), and chain termination reactions (vinylene/vinyl = 83.4%–93.6%). Electron-donating groups at benzhydryl of aniline showed positive influence on the rate of monomer insertion and chain propagation, resulting in high catalytic activity and polymer molecular weights. Change of chain walking and chain termination rate with reaction temperature resulted in polyethylene with varied physical states from sticky wax to thick oil. Most importantly, β-elimination is the predominant route for chain termination reaction and produces polyethylene with a high ratio of internal double bonds (─CH═CH─/CH₂═CH─ up to 93.6%). These macromers are important for post-modification processes.

To elucidate the hydrogenation process of formate species on Cu-based model catalysts, we investigated the thermal process of formic acid on the clean Cu(997) surface and the H-adsorbed Cu(997) surface using temperature programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS). In the TPD spectra of HCOOH/H/Cu(997), desorption of formaldehyde was observed at 260–410 K. By comparing the results for the clean Cu(997) surface with those for the H-adsorbed Cu(997) surface, we have found that hydrogenated species are newly formed by the presence of hydrogen on Cu(997) after heating to 300 K using HREELS; the intermediate species is assigned to dioxymethylene. These results indicate that some of formate species are hydrogenated to dioxymethylene below 300 K and the dioxymethylene is decomposed and desorbed as formaldehyde between 260 and 410 K. In addition, the bidentate formate species at step sites are predominantly involved in the hydrogenation reaction. On the other hand, most of the bidentate formate species on the terrace are decomposed and desorbed as CO₂ and H₂; these formate species may appear as spectator species. We conclude that the Cu step site plays an important role in the hydrogenation of formate species to dioxymethylene and formaldehyde.

The surface properties of nanostructured materials, especially the role of facets, have emerged as a central focus in improving photoelectrochemical (PEC) performance. High-/low-index facets in semiconductor nanostructures feature unique atomic structures, chemical reactivity, and electronic characteristics, critically influencing light absorption, charge separation, and catalytic activity, significantly enhancing the PEC efficiency. High-index facets, distinguished by distinct atomic structures, generally demonstrate enhanced catalytic activity owing to their higher surface energy and increased density of reactive sites. However, they tend to be less stable compared to low-index facets. In contrast, low-index facets offer better thermodynamic stability but may have reduced catalytic activity. Achieving the balance between these properties is critical for designing materials that maximize performance and durability in PEC water-splitting applications. Recent developments in synthetic techniques, including hydrothermal/solvothermal procedures and epitaxial growth, have facilitated precise control over the exposure of specific facets, allowing for the customization of nanostructured materials to optimize efficiency. This review paper comprehensively analyzes the faceted materials and their diverse methodologies for synthesis (ex situ and in situ), modification, and transformation of geometrical arrangements into facets of various semiconductor materials. A deeper understanding of crystal-facet engineering in crystals with tailored configurations has revealed substantial potential for the systematic design and synthesis of advanced micro-/nanostructures.

The impact of replacing Zr⁴⁺ with Hf⁴⁺ as the metal site on CO₂ adsorption and catalytic activity in CO₂ fixation reaction with epoxide under mild conditions was investigated in UiO66-NH₂ grafted with carbodiimides N,N′-dicyclohexylcarbodiimide (DCC) and N,N′-diisopropylcarbodiimide (DIC) (UiO66(M)-DCCBr and UiO66(M)-DICBr; M = Zr and Hf). Leveraging on Hf⁴⁺’s greater oxophilicity and stronger M—O bonds, Hf-based UiO66-NH₂ materials exhibited increased CO₂ adsorption capacity, influencing the catalytic performance in CO₂ fixation with epoxides. The materials were characterized by multiple techniques such as PXRD, FTIR, TGA, SEM, elemental analysis, as well as N₂ and CO₂ adsorption equilibrium measurements. UiO66(Hf)-DCCBr and UiO66(Hf)-DICBr demonstrated superior activity compared to their Zr-based counterparts with high yield and TOF (14.6 and 11.9 h⁻¹, respectively) under milder conditions (0.1 MPa, 90 °C, 16 h, co-catalyst-free and solvent-free). These findings underscore the pivotal role of unsaturated metal sites in enhancing the catalytic efficacy of guanidinium ionic UiO66-NH₂ materials. Moreover, these catalysts exhibit excellent thermal stability and can be recycled and reused at least five times without a noticeable reduction in their catalytic efficiency.

In this study, we report a photoredox-catalyzed, visible-light-mediated three-component synthesis of β-ketosulfonamides from silyl enol ethers, N-aminopyridinium salts, and the sulfur dioxide (SO₂) surrogate DABSO (1,4-diazabicyclo[2.2.2]octane·bis (sulfur dioxide) adduct). Eosin Y is used as readily available and cost-efficient organic photoredox catalyst. This method is based on the photochemical generation of sulfamoyl radicals as key intermediates from N-aminopyridinium salts as nitrogen radical precursors and DABSO as an easy-to-handle, solid SO₂ source. Trapping of the in situ-generated sulfamoyl radicals with silyl enol ethers affords pharmaceutically relevant β-ketosulfonamides in 63%–91% yields.

Developing efficient heterogeneous catalysts for activating CO₂ is of considerable interest for achieving carbon neutrality. Therefore, many researchers have devoted a lot of effort to design and develop various porous materials-based catalysts for CO₂ conversion. Catalysts with high activity and stability for CO₂ conversion are crucial for easy commercialization, but it remains a significant challenge to develop these catalysts. Herein, we report the fabrication of Ni-functionalized mesoporous silica with 3D mesoporous structure, cage-type pores, and different Ni contents for achieving enhanced CO₂ methanation and stability. The highly ordered mesoporous structure of SBA-1 offers a high surface area (1315 m² g⁻¹) that helps to anchor a significant amount of nickel nanoparticles. Insight into the structure of the catalyst and fine-tuning of metal-support interaction were in-depth, characterized by the combination of X-ray diffraction, electron imaging, and spectroscopic tools. The prepared Ni-functionalized SBA-1 materials exhibit an ordered mesoporous structure and the specific surface area decreases with increasing the concentration of the Ni on the porous channels of SBA-1. The optimized Ni-functionalized SBA-1 yielded 80.1% conversion with a CH₄ selectivity of 96.9% at a gas hourly space velocity (GHSV) of 21,000 mLg_cat⁻¹h⁻¹ under the optimized reaction conditions. Temperature-programmed surface reaction (TPSR) studies suggest a mechanism involving CO₂ dissociation into CO. The Ni-loaded SBA-1 catalyst demonstrated remarkable stability over five consecutive 24 h cycles, indicating its promising potential for practical application in sustainable energy production and greenhouse gas mitigation.