ChemCatChem最新文献

Cyclic organic carbonates are defined as key compounds for a sustainable chemical economy. Their synthesis from CO₂ under mild conditions is a useful way to valorise this greenhouse gas as carbon source. Even if a wide range of catalysts were described to promote the carbon dioxide cycloaddition into epoxides, only few ones concern enzymatic systems. The zinc–l-histidine active site of carbonic anhydrase inspired the present work, pointing out that the imidazole moiety of the amino acid ligand has a crucial role. An extensive study was undertaken to establish the structure–activity relationship of imidazole derivatives, zinc salts, and their respective catalytic activity in the CO₂ cycloaddition reaction. The effect of aromatic, alkyl, or iodine substituents and their position in N-heterocycles were highlighted. A synergic effect was noted when combining imidazole compounds with zinc salts. The optimization of reaction conditions emphasised the in situ ZnI₂–1-methylimidazole catalytic system, which is selective toward cyclic styrene carbonates and efficient under solvent-free mild conditions (50 °C, atmospheric CO₂ pressure). Once reusing tests confirmed the catalytic system robustness, the reaction scope was enlarged to several epoxides resulting in 84%–99% yields of their corresponding cyclic carbonates.

A process combining aldol condensation and hydrogenation of bio-based cyclopentanone (CPO) in a one-pot reaction is proposed. Cu-based bifunctional catalysts obtained from hydrotalcite-type precursors were found highly active in mild reaction conditions (i.e., 130–170 °C), producing valuable bicyclic (C10) and tricyclic (C15) aliphatic alcohols/ketones with interesting application as sustainable aviation fuel (SAF) precursors with enhanced properties. The presence of surficial strong basic sites active in aldol condensation, together with the formation of highly dispersed copper nanoparticles able to catalyze C═C and C═O hydrogenation (TOF of 0.06–0.16 s⁻¹), assured high catalytic efficiency and fine control of the products nature and distribution. From the optimization of both catalysts formulation and reaction conditions it was found that, properly tuning the Cu content, it is possible to drive products distribution towards the production of bicyclic (C10) aliphatic alcohol with high selectivity (75% at total CPO conversion, when Cu = 10 wt %, at 170 °C, 1.0 MPa of H₂) and short reaction time (4 h). The optimized catalyst formulation showed impressive stability over multiple reaction/regeneration cycles, demonstrating the high potential of the proposed catalytic process for future applications in sustainable biofuels production.

Layered double hydroxides (LDHs) have recently attracted much attention in the scientific community as a prominent catalyst for oxygen evolution reaction (OER) because they are economical, extremely stable, and highly active. Literature on LDH alone and their hybrids for catalyzing water oxidation are readily available, but LDH catalyzing hydrogen evolution reaction (HER) is meager. Here, we synthesized Co/Al-based LDH systems that efficiently perform as bifunctional electrocatalysts for both HER and OER. Exfoliation of this layered material via anion intercalation into a few layers further enhanced its activity. In this work, we reported the synthesis of Co/Al LDHs via coprecipitation followed by hydrothermal method and different surfactant-functionalized LDHs (with anionic surfactant: SDS, cationic surfactant: CTAB, and nonionic surfactant: PEG 4000). SDS-modified LDH (s LDH) showed notable stability and competent results in hydrogen evolution in addition to oxygen evolution. The exfoliation of s LDH caused enhancement in the high specific surface area about 6.8 times compared to pristine LDH, as evident from BET data. The onset potential for HER as obtained from the polarization curve for s LDH is −0.41 V versus RHE, with Tafel slope of 67.4 mV/dec. Similarly, OER onset potential and corresponding Tafel slope are 1.53 V versus RHE at 10 mA/cm² and 90.2 mV/dec, respectively.

Bimetallic carbides, especially based on molybdenum carbide, proved to be a promising hydrodeoxygenation (HDO) catalyst, with enhanced selectivity towards C─O bonds cleavage. However, catalysts are generally investigated using limited model components derived from only one of the biopolymers in biomass (either lignin or carbohydrates), therefore, HDO of raw biomass-derived bio-oil still remains a challenge, as it contains molecules of different functionalities. This paper presents a systematic comparison of the monometallic carbide, Mo₂C, with the novel bimetallic carbide incorporating W using representative bio-oil components of different functionalities and derived from different bio-polymers components of biomass. We employed quantum mechanical investigation to reveal that the W-doped Mo₂C carbide (MoWC) catalyst with increased oxophilicity, owing to tungsten incorporation, can perform HDO of real bio-oil more effectively in comparison to its monometallic counterpart (Mo₂C) using six substrates representing different components of bio-oil. We showed MoWC can selectively cleave both single/double (C─O/C═O) bonds with similar barriers in comparison to Mo₂C which can only selectively cleave single C─O bonds. This observation was consistent for 5-HMF, Acetic acid, and Methyl Glyoxal. We also showed that MoWC outperforms its metallic counterpart Mo₂C in the HDO for aromatic and carbohydrates components.

The use of EtOH as hydrogen donor is remarkably under explored in transfer hydrogenation reactions, even though EtOH represents an appealing hydrogen source. With the cationic ruthenium complex [Ru(PYA)(cymene)]⁺, 1, containing a N,N-bidentate amino-functionalized pyridinium amidate (PYA) ligand as catalyst precursor, we here demonstrate the first example of chemoselective room temperature transfer hydrogenation of the C═C bond in α,β-unsaturated ketones using EtOH as benign hydrogen source to yield a variety of functionalized ketones. The reaction proceeds under mild conditions with K₂CO₃ as base and conventiently at room temperature. A broad substrate scope, including various functionalized α,β-unsaturated carbonyl groups, demonstrates the general applicability of this method. Preliminary mechanistic studies suggest the formation of an alkoxide complex [1]–OEt as an initially formed species, and the requirement for EtOH to induce hydride transfer, suggesting a protic activation of the catalyst.

In this study, we explored the use of Mes-Acr-MeClO₄ as a visible light photocatalyst for multicomponent reactions involving quinoxalin-2(1H)-ones with CBrCl₃ and styrene. The method showcases regioselective functionalization of quinoxalin-2(1H)-ones in a three-component system, forming two C─C bonds in one pot. Mechanistic investigations suggest a radical-mediated pathway, initiated by the photoexcitation of Mes-Acr-MeClO₄, followed by halogen atom abstraction from CBrCl₃. This approach provides a versatile and sustainable route for quinoxalin-2(1H)-one functionalization, with Mes-Acr-MeClO₄ effectively facilitating the photocatalyzed multicomponent reaction under mild conditions and visible light irradiation, yielding high selectivity and efficiency.

ε-Caprolactam (CPL) is industrially produced by Beckmann rearrangement of cyclohexanone oxime (CHO) under fuming sulfuric acid, resulting in corrosive and environmental issues. Herein, we prepared triethylamine hydrochloride (TEAHC) and ZnCl₂ formed deep eutectic solvent (DES) [TEAHC:2ZnCl₂] with Brønsted and Lewis acid sites for efficient liquid rearrangement, achieving 100% conversion of CHO and 95.5% yield of CPL at 80 °C for only 1 h. The results show that ZnCl₂ in [TEAHC:2ZnCl₂] can promote the detachment of proton, which acts as Brønsted acid site combined with another ZnCl₂ molecule to synergistically catalyze the reaction. In the Brønsted acid catalyzed process, the nitrogen atom in CHO as reactive site can be readily attacked by the proton to form protonated CHO, which subsequently undergoes rearrangement. By adding ZnCl₂ into TEAHC to obtain [TEAHC:2ZnCl₂], the formation of ZnCl₂-CHO complex results in a significant reduction in reaction energy barrier through synergistic effect of Brønsted and Lewis acids. Particularly, the fitted reaction kinetics and low activation energy also confirm the rearrangement can occur under low reaction temperature. Thus, the DESs with efficient catalytic performances for ketoxime rearrangements provide a potential method to design active sites for Beckmann rearrangements of oximes under mild reaction conditions.

Covalent organic frameworks (COFs) serve as an excellent foundation for heterogeneous photocatalysis. Herein, we synthesized an anthraquinone-based COF (TpAQ) on a gram scale via a mechanochemical grinding pathway. This COF was employed as a visible-light-harvesting photocatalyst for selective fluorination of benzylic C─H bonds and perfluoroalkylation of arenes. The carbonyl core in the anthraquinone linker facilitated benzylic fluorination through a hydrogen atom transfer (HAT) pathway. Control experiments and photophysical analysis were conducted to gain deeper insight into the reaction mechanism. The recyclability up to the fifth cycle without significant loss of yield (>90%) highlighted the robustness of the catalyst. This reaction strategy was also executed on a gram scale to validate the scalability of the protocol.

Hydrothermal growth of ZnSn(OH)₆ nanograss on ZnO-coated FTO substrates is demonstrated. Effect of surfactants addition (polyvinylpyrrolidone and polyethylene glycol), precursor concentration, and reaction temperature on surface morphology of ZnSn(OH)₆ nanograss are investigated. Addition of surfactant in precursor solution results in growth of approximately 20–30 nm thick nanograss morphology with varying orientation. The nanograss grow longer by increasing the concentration of precursors solution. The grown ZnSn(OH)₆, exhibits XRD peaks corresponding to cubic phase ZnSn(OH)₆. Optical bandgap of the grown nanograss are calculated in the range from ∼3.0 to 3.5 eV. The nanograss photoanode grown with PEG surfactant (at 200 °C) has shown the highest photocurrent of 2.2 mA/cm² at RHE 1.23V_RHE and photoconversion efficiency of 1.4% at 0.46 V_RHE. The longer nanograss has shown lower charge transfer resistance and higher charge carrier concentration, which is favorable for enhancing the PEC performance.

This study is focused on examining the incorporation of oxidative dehydrogenation into the aromatization of ethane, utilizing thermodynamic analysis and catalytic experiments. The catalysts were characterized by inverse temperature programmed reduction, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The results indicated that a blend of the M1 catalyst, containing oxides of vanadium, niobium, and tellurium, with H-ZSM-5, serves as an effective catalyst system for the oxidative aromatization of ethane at T = 380 °C. The M1's role in the oxidative dehydrogenation of ethane contributes to de-bottlenecking the essential step of the reaction. On the zeolitic catalyst aromatic compounds are formed from a surface hydrocarbon pool. In parallel, the oxidation of these intermediates was observed. Also, the formation of paraffins through H-transfer was evident from the catalytic results. Although the zeolite underwent significant deactivation due to coking, the M1 catalyst demonstrated highly stable activity. Interestingly, the system did not show any synergistic effects. Based on the structure-activity relation of the catalytic system a reaction mechanism is proposed.