Chinese Journal of Catalysis最新文献

The electronic configuration of central metal atoms in single-atom catalysts (SACs) is pivotal in electrochemical CO₂ reduction reaction (eCO₂RR). Herein, chalcogen heteroatoms (e.g., S, Se, and Te) were incorporated into the symmetric nickel-nitrogen-carbon (Ni-N₄-C) configuration to obtain Ni-X-N₃-C (X: S, Se, and Te) SACs with asymmetric coordination presented for central Ni atoms. Among these obtained Ni-X-N₃-C (X: S, Se, and Te) SACs, Ni-Se-N₃-C exhibited superior eCO₂RR activity, with CO selectivity reaching ~98% at −0.70 V versus reversible hydrogen electrode (RHE). The Zn-CO₂ battery integrated with Ni-Se-N₃-C as cathode and Zn foil as anode achieved a peak power density of 1.82 mW cm^–2 and maintained remarkable rechargeable stability over 20 h. In-situ spectral investigations and theoretical calculations demonstrated that the chalcogen heteroatoms doped into the Ni-N₄-C configuration would break coordination symmetry and trigger charge redistribution, and then regulate the intermediate behaviors and thermodynamic reaction pathways for eCO₂RR. Especially, for Ni-Se-N₃-C, the introduced Se atoms could significantly raise the d-band center of central Ni atoms and thus remarkably lower the energy barrier for the rate-determining step of *COOH formation, contributing to the promising eCO₂RR performance for high selectivity CO production by competing with hydrogen evolution reaction.

Electrochemical CO₂ reduction to produce value-added chemicals and fuels is one of the research hotspots in the field of energy conversion. The development of efficient catalysts with high conductivity and readily accessible active sites for CO₂ electroreduction remains challenging yet indispensable. In this work, a reliable poly(ethyleneimine) (PEI)-assisted strategy is developed to prepare a hollow carbon nanocomposite comprising a single-site Ni-modified carbon shell and confined Ni nanoparticles (NPs) (denoted as Ni@NHCS), where PEI not only functions as a mediator to induce the highly dispersed growth of Ni NPs within hollow carbon spheres, but also as a nitrogen precursor to construct highly active atomically-dispersed Ni-Nx sites. Benefiting from the unique structural properties of Ni@NHCS, the aggregation and exposure of Ni NPs can be effectively prevented, while the accessibility of abundant catalytically active Ni-Nx sites can be ensured. As a result, Ni@NHCS exhibits a high CO partial current density of 26.9 mA cm^–2 and a Faradaic efficiency of 93.0% at −1.0 V vs. RHE, outperforming those of its PEI-free analog. Apart from the excellent activity and selectivity, the shell confinement effect of the hollow carbon sphere endows this catalyst with long-term stability. The findings here are anticipated to help understand the structure-activity relationship in Ni-based carbon catalyst systems for electrocatalytic CO₂ reduction. Furthermore, the PEI-assisted synthetic concept is potentially applicable to the preparation of high-performance metal-based nanoconfined materials tailored for diverse energy conversion applications and beyond.

Metal halide perovskite (MHP) has become one of the most promising materials for photocatalytic CO₂ reduction owing to the wide light absorption range, negative conduction band position and high reduction ability. However, photoreduction of CO₂ by MHP remains a challenge because of the slow charge separation and transfer. Herein, a cobalt single-atom modified nitrogen-doped graphene (Co-NG) cocatalyst is prepared for enhanced photocatalytic CO₂ reduction of bismuth-based MHP Cs₃Bi₂Br₉. The optimal Cs₃Bi₂Br₉/Co-NG composite exhibits the CO production rate of 123.16 μmol g^–1 h^–1, which is 17.3 times higher than that of Cs₃Bi₂Br₉. Moreover, the Cs₃Bi₂Br₉/Co-NG composite photocatalyst exhibits nearly 100% CO selectivity as well as impressive long-term stability. Charge carrier dynamic characterizations such as Kelvin probe force microscopy (KPFM), single-particle PL microscope and transient absorption (TA) spectroscopy demonstrate the vital role of Co-NG cocatalyst in accelerating the transfer and separation of photogenerated charges and improving photocatalytic performance. The reaction mechanism has been demonstrated by in situ diffuse reflectance infrared Fourier-transform spectroscopy measurement. In addition, in situ X-ray photoelectron spectroscopy test and theoretical calculation reveal the reaction reactive sites and reaction energy barriers, demonstrating that the introduction of Co-NG promotes the formation of *COOH intermediate, providing sufficient evidence for the highly selective generation of CO. This work provides an effective single-atom-based cocatalyst modification strategy for photocatalytic CO₂ reduction and is expected to shed light on other photocatalytic applications.

Propane dehydrogenation (PDH) on Ga/H-ZSM-5 catalysts is a promising reaction for propylene production, while the detail mechanism remains debatable. Ga₂O₂²⁺ stabilized by framework Al pairs have been identified as the most active species in Ga/H-ZSM-5 for PDH in our recent work. Here we demonstrate a strong correlation between the PDH activity and a fraction of Ga₂O₂²⁺ species corresponding to the infrared GaH band of higher wavenumber (GaHHW) in reduced Ga/H-ZSM-5, instead of the overall Ga₂O₂²⁺ species, by employing five H-ZSM-5 supports sourced differently with comparable Si/Al ratio. This disparity in Ga₂O₂²⁺ species stems from their differing capacity in completing the catalytic cycle. Spectroscopic results suggest that PDH proceeds via a two-step mechanism: (1) C–H bond activation of propane on H-Ga₂O₂²⁺ species (rate determining step); (2) β-hydride elimination of adsorbed propyl group, which only occurs on active Ga₂O₂²⁺ species corresponding to GaHHW.

Utilizing single atom sites doping into metal oxides to modulate their intrinsic active sites, achieving precise selectivity control in complex organic reactions, is a highly desirable yet challenging endeavor. Meanwhile, identifying the active site also represents a significant obstacle, primarily due to the intricate electronic environment of single atom site doped metal oxide. Herein, a single atom Cu doped TiO₂ catalyst (Cu₁-TiO₂) is prepared via a simple “colloid-acid treatment” strategy, which switches aniline oxidation selectivity of TiO₂ from azoxybenzene to nitrosobenzene, without using additives or changing solvent, while other metal or nonmetal doped TiO₂ did not possess. Comprehensive mechanistic investigations and DFT calculations unveil that Ti-O active site is responsible for triggering the aniline to form a new PhNOH intermediate, two PhNOH condense to azoxybenzene over TiO₂ catalyst. As for Cu₁-TiO₂, the charge-specific distribution between the isolated Cu and TiO₂ generates unique Cu₁-O-Ti hybridization structure with nine catalytic active sites, eight of them make PhNOH take place spontaneous dissociation to produce nitrosobenzene. This work not only unveils a new mechanistic pathway featuring the PhNOH intermediate in aniline oxidation for the first time but also presents a novel approach for constructing single-atom doped metal oxides and exploring their intricate active sites.