ChemCatChem最新文献

The efficacy of hydrogen activation by Ni species is a critical determinant of the catalytic performance in CO₂ methanation. Herein, the nature of Ni species in CeZrO_x/Ni was modulated by altering the calcination atmosphere. The CeZrO_x/Ni─O demonstrated excellent low-temperature methanation activity, achieving a CO₂ conversion of 94.3% at 225°C. This value is 5.8 times higher than that of the CeZrO_x/Ni─N. The characterization results indicated that Ni species formed in oxygen-containing atmospheres exhibited high dispersion, which facilitated the formation of Ni–MO_x interfaces and thereby promoted the activation of CO₂ and H₂. In contrast, under oxygen-free conditions, Ni species formed a strong interaction with oxygen atoms from CeZrO_x, which suppressed the activation of H₂. In situ DRIFT spectra demonstrated that the reaction involved dual pathways, namely the formate pathway and the CO pathway. The abundant Ni–O–M interfaces substantially enhanced CO₂ adsorption and conversion to formate species, thereby establishing the formate pathway as dominant.

This study focuses on the catalytic transformation of a lignin model compound, 4-propylguaiacol, without external hydrogen. The reaction using a Ni/MgO catalyst and water as the solvent, conducted at 220°C under 5 bar N₂ for 2 h, achieved 97.8% conversion and 94.8% selectivity toward phenolic products. During the reaction, the methoxy group in 4-propylguaiacol is cleaved from the aromatic ring at Ni active sites and subsequently reacts with hydrogen radicals generated from water dissociation to form methanol. The methanol then undergoes aqueous-phase reforming, providing additional in-situ hydrogen to drive the hydrodeoxygenation process. The Ni/MgO catalyst showed good recyclability over three consecutive cycles, with only a slight decline in activity. Furthermore, this catalyst was applied to the depolymerization of real lignin, and the effects of reaction parameters on product yield were investigated. Among the tested conditions, a maximum monomer yield of 76.7 wt% was obtained at 280°C under 5 bar N₂ for 6 h.

The urgent need to decarbonize the chemical industry is placing growing emphasis on the electrification of industrial processes. Dry methane reforming (DRM) offers a promising route for syngas (H₂/CO) production through the simultaneous conversion of two major greenhouse gases, CO₂ and CH₄. However, the process is hampered by modest catalytic performance and fast deactivation. In this study, we address these limitations by implementing localized, rapid magnetic induction heating (IH), using a graphene-coated NiCo/SiC catalyst as a susceptor, which ensures efficient heat delivery and enhanced reaction control. The results clearly evidence that IH significantly enhances both the catalytic activity and long-term stability of the DRM process at relatively low reaction temperatures. Importantly, this approach is compatible with a wide range of existing catalyst systems, including industrial formulations, and offers a practical pathway for retrofitting conventional reactors. Beyond performance gains, IH also shows potential as a strategy for chemical energy storage, aligning with current electrification and sustainability goals in the chemical sector.

Imidazolones serve as a crucial framework for a range of applications, spanning from medicine, natural products, agriculture, and beyond. Despite showing significant promise in diverse areas, their preparatory methods are not widely developed. Herein, we report a simple one-pot transition metal-free approach for the synthesis of substituted imidazolones. The protocol encompasses a broad substrate scope with good yields. To gain insight into the present protocol, various control experiments and extensive computational calculations were performed.

Highly selective carbon monoxide production can be achieved during the electrolysis of carbon dioxide using a cathode catalyst composed of silver nanoparticles loaded onto a carbon support (Ag/C). Although generating abundant Ag species is desirable for efficient CO₂ electrolysis, conventional methods tend to produce relatively large Ag particles at high loading levels. In this paper, an advanced Ag/C electrocatalyst is produced via ultrasonic reduction (Ag(USR)/C). Importantly, the activity of this electrocatalyst was demonstrated to be superior to those of Ag/C cathodes prepared via conventional methods. This activity was retained under various conditions. In particular, CO was formed during electrolysis when 10 vol.% CO₂ was supplied to the Ag(USR)/C cathode, while only H₂ was evolved on the Periodical Ag/C cathodes. Abundant Ag nanoparticles measuring a few nanometers in diameter were detected on the Ag(USR)/C electrocatalyst surface, whereas significantly larger Ag species were observed on the Periodical Ag/C catalysts. Additionally, electrochemical impedance spectroscopy suggested that electrons were injected into CO₂ more efficiently when the Ag(USR)/C was employed. Accordingly, these small Ag nanoparticles exhibited superior activity in the efficient low-concentration CO₂ electrolysis and 100% CO₂ electrolysis processes. These results confirm the high CO₂ electrolysis activity of the Ag(USR)/C cathode.

A naturally sourced imine reductase (IRED) was identified from the UniProt database and thoroughly investigated, leading to the identification of an IRED (Thermostaphylospora chromogena) typically toward the S-isomer. The mutation E127P/E221A/S236A (denoted as M3) was obtained through combinatorial mutagenesis, which exhibited a wider pH range, significantly improved catalytic activity, and enhanced stability compared to the wild-type TcIR. M3 demonstrated an enzyme activity of 307.28 ± 3.35 U/g_protein and a 7.78-fold increase in catalytic efficiency, clearly outperforming that of TcIR. A dual enzyme-catalyzed asymmetric synthesis of (S)-1-methyl-1,2,3,4-tetrahydroisoquinoline ((S)-1-MeTIQ) from 100 mM 1-methyl-3,4-dihydroisoquinoline (1-MeDIQ) was constructed by combining M3 with formate dehydrogenase (FDH, for coenzyme regeneration). This cascade biocatalytic system achieved remarkable results, with a high conversion (> 99%) of 1-MeDIQ and enantioselectivity (ee value > 98%) of (S)-1-MeTIQ under optimized reaction conditions. Additionally, this dual-enzyme system was extended to the asymmetric reduction of more cyclic imine substrates, achieving excellent conversion (> 96%) and high ee values > 96%. These findings reveal that M3 is a promising biocatalyst for the efficient, scalable, and stereoselective synthesis of chiral tetrahydroisoquinolines and other chiral N-heterocyclic compounds.

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