ChemCatChem最新文献

The commercialization of the oxidative coupling of methane (OCM) process is hindered by its low C₂ hydrocarbon yield and C₂H₄/C₂H₆ product ratio. In this work, a dual-bed catalytic system comprising a SrCl₂ additive layer packed above the classic Na₂WO₄-MnO_x/SiO₂ catalyst has been proposed. The promoting effect of the introduced SrCl₂ additives is revealed. On one hand, SrCl₂ undergoes in situ oxidative dehalogenation to generate chloromethane active intermediates, which trigger chlorine radical chain transfer reactions in the OCM catalyst layer, significantly reducing the energy barriers of methane activation and ethane dehydrogenation. On the other hand, SrCl₂, with a high melting point, prevents the metal chlorides from evaporating and covering the catalyst active sites, but still releases abundant chloromethane intermediates to participate in the OCM reaction at a moderate rate. Consequently, a more reactive and stable OCM reaction was achieved, with a C₂ yield up to 25% and a C₂H₄/C₂H₆ ratio around 5 in 20 h of continuous operation. This work provides an efficient strategy for a highly active and stable OCM process.

Noble metals on carbon supports are promising catalysts for the hydrodeoxygenation of carbohydrate-rich waste streams into naphtha-range alkanes (C₅-C₉), key intermediates for fuels and chemicals. Among tested catalysts, Ru/C showed the highest activity due to its oxophilicity but suffered from excessive CC cleavage, lowering C₆ alkane selectivity (39 C%). Pt/C achieved higher C₆ alkane selectivity (56 C%) by suppressing formation of intermediates prone to C-C scission, though its high cost limits scalability. To improve Ru/C performance, hydrothermal pretreatments with and without H₄SiW₁₂O₄₀ in solution were applied, boosting C₆ alkane yield to 56 C% and C₅-C₆ alkane yield to 66 C%, surpassing Pt/C catalysis. Ru dispersion remained intact at short residence times during pretreatment without H₄SiW₁₂O₄₀, while surface acidity was reduced, hindering C─O cleavage. The addition of H₄SiW₁₂O₄₀ during pretreatment restored acidity, incorporating reduced WOx species in the catalyst pores. However, excessive acid incorporation led to pore blockage and Ru oxidation to a less active RuO₂ phase. These findings emphasize the need to carefully balance acidity, metal oxidation state, particle size, and support porosity to optimize naphtha production from renewable carbohydrates.

Efficient techniques for removing off-flavor substances are urgently needed. This study prepared the rGO/g-C₃N₄/TiO₂ composite to investigate its photocatalysis performance for removing geosmin (GSM) and 2-methylisoborneol (2-MIB) in water under ultraviolet (UV) light irradiation. The effects of different factors on the removal efficiency of GSM and 2-MIB were deeply discussed. The results indicated that the introduction of rGO effectively promoted the separation of photogenerated charge carriers while the heterojunction formed by g-C₃N₄ and TiO₂ broadened the spectral response range. Over 90% of 2-MIB and GSM were removed within 60 min under the optimal conditions. Co-existing HCO₃⁻, CO₃²⁻, and NO₂⁻ in water inhibited the removal of off-flavor substances by photocatalysis. The removal of GSM did not depend on pH, whereas 2-MIB showed improved removal at neutral conditions. The catalytic activity of rGO/g-C₃N₄/TiO₂ remained stable after three cycles of use. The UV photocatalysis of rGO/g-C₃N₄/TiO₂ relied on the synergistic effect of the Type-II heterojunction and rGO to generate more active species such as ·OH, ¹O₂, O₂·⁻, and h⁺. The removal of GSM was dominated by ·OH, whereas 2-MIB removal was controlled by ¹O₂. This study provided a feasible approach for the efficient removal of off-flavor substances in water.

Chiral sulfoxides are important motifs in pharmaceuticals, yet their asymmetric synthesis remains challenging due to the need for stereocontrol. While bio-oxidation provides an attractive route, the lack of robust high-throughput screening methods hinders the development of enantioselective sulfoxide synthases. Herein, we developed a high-throughput assay combining sulfoxide reductases (MsrA/B) with a DL-dithiothreitol and 5,5’-dithiobis (2-nitrobenzoic acid) chromogenic system. This platform enables the simultaneous assessment of both catalytic efficiency and enantioselectivity, with colorimetric signals showing a linear correlation (R² = 0.99) against HPLC-validated enantiomeric excess. As a proof of concept, we screened 2880 engineered variants of recombinant unspecific peroxygenase from Agrocybe aegerita (rAaeUPO), a known thioether-oxidizing enzyme. This method allows the identification of mutants with complementary enantioselectivity (95.2% ee (R) or 10.3% ee (S)). In addition, the modular design of this assay—exploiting the stereo-complementarity of MsrA/B toward sulfoxides—provides a general framework for developing other stereoselective oxidoreductases for thioether oxidation.

The selective reduction of halogenated nitrobenzenes to halogenated anilines represents a fundamental challenge in heterogeneous catalysis due to competing dehalogenation pathways that compromise product selectivity. Herein, we report ferritin-templated iridium nanocatalysts (Ir@FnNC) that achieve unprecedented chemoselectivity by transforming the protein cage from a passive support into an active “nanoreactor.” The ferritin scaffold enables precise control over iridium nanoparticle size (2.8–4.7 nm) and generates mixed Ir⁰/Ir^IV oxidation states with strong metal-protein electronic coupling, as evidenced by XPS binding energy shifts and emergent ligand-to-metal charge-transfer photoluminescence. Remarkably, Ir@FnNC600 delivers 99% conversion and 99% chemoselectivity toward p-chloroaniline with turnover frequencies 65-fold higher than homogeneous benchmarks, while conventional catalysts produce only dehalogenated aniline. Molecular dynamics simulations reveal a sophisticated three-stage substrate recognition mechanism where amino acid residues (Ser118, Ala121, Phe35, Arg52) orchestrate substrate pre-concentration and orientation, protecting C–Cl bonds while directing nitro group reduction. Mechanistic studies unveil a unique azobenzene-mediated pathway involving chlorine-retaining intermediates (p-chlorophenylhydroxylamine, 4,4'-dichloroazobenzene) that are absent in conventional systems. This bio-inorganic hybrid strategy demonstrates how evolutionary optimization principles can be harnessed to achieve catalytic transformations impossible with traditional heterogeneous catalysts, establishing a versatile platform for developing programmable selectivity in sustainable chemical synthesis.

Poly (ionic liquid)s (PILs) are promising catalysts for conversion of CO₂ and epoxides into cyclic carbonates, which could mitigate greenhouse effects while generating economic benefits. To achieve efficient utilization of active sites of PILs, a series of swelling PILs were synthesized in this work by copolymerization of ionic liquid monomer (EIL) with flexible polyethylene glycol dimethacrylate (PEGDMA) at varying molar ratio. The resulting swelling PILs showed significantly improved catalytic activity compared to nonswollen PEIL obtained by EIL self-polymerization. Additionally, a lower EIL/PEGDMA ratio during synthesis increased the flexible segment length between ionic liquid sites, which enhanced the swelling ability of PILs and further improved the catalytic activity. Among the synthesized PILs, the optimized P(EIL-co-EG)1.0, which showed the strong swelling ability, achieved catalytic performance comparable to that of monomers homogeneous catalysis, yielding 93.4% PC under the reaction conditions optimized (120°C, 1.5 mol% catalyst, 2 MPa CO₂, 3 h). Furthermore, P(EIL-co-EG)1.0 demonstrated broad substrate scope toward various epoxides. Finally, based on FT-IR and NMR spectroscopy, a plausible catalytic mechanism was proposed. This study offers valuable insights into the enhancement of heterogeneous catalyst efficiency and the rational design of quasihomogeneous catalytic systems.