Journal of Catalysis最新文献

Advancing efficient catalysts for oxygen reduction reaction (ORR) or oxygen evolution reaction (OER) is imperative for commercializing emerging energy devices. Using density functional theory (DFT) calculations, we propose doping different transition metal (TM) atoms to regulate the electronic structures of the two-dimensional 1T-HfTe₂ monolayer to achieve bifunctional catalysis for the ORR/OER. Due to the small electronegativity of the Hf atom, we found the doped TM atoms can generally form anion centers by accepting abundant charges from the Hf interlayer. At the same time, the highly conductive 1T-HfTe₂ contributes to the charge transfer between the active center and the reaction intermediates, rendering the designed SACs the tunable activity for the reactions. By comparing the theoretical overpotentials of ORR and OER on 15 single-atom catalysts (SACs), Pt-doped system exhibits excellent catalytic activity for both ORR and OER, outperforming the traditional Pt(1 1 1) and RuO₂(1 1 0) catalysts. Based on the charge transfer mechanism, we clarified that the doped TM atoms act as a ‘bridge’ to transfer the electrons from the substrate to the reaction intermediates, thereby effectively contributing to the improvement of catalytic activity. In summary, our study shows that, by doping appropriate TM atoms, the intrinsic inert HfTe₂ can be activated toward efficient ORR/OER. This could provide some guidance for the design of new two-dimensional ORR/OER bifunctional catalyst materials.

Copper-zinc-alumina (Cu/ZnO/Al₂O₃) has been utilized as the leading catalyst for industrial methanol synthesis via hydrogenation of CO and CO₂ for more than 50 years. Understanding the nature of active Zn sites at the atomic level is vital for gaining insight into the reaction mechanism and rational design of more efficient Cu/ZnO catalysts for methanol synthesis but remains greatly challenging and has been intensively debated for decades. In this mini-review, we first describe the fundamental insights obtained from well-defined model catalysts and then summarize the recent experimental evidence with respect to dynamic structural and electronic changes in the active Zn phase under realistic working conditions by in situ/operando microscopy/spectroscopy and surface site titration using probing molecules. In the following, we discuss the catalytic mechanism of diverse active structures by theoretical calculations and simulations. Therefore, the critical role of interfacial sites between metallic Cu and ZnO, especially those with oxygen defects, in methanol synthesis via CO₂ hydrogenation is emphasized. Finally, we discuss the technical challenges and perspectives in understanding the origins of this Cu-ZnO synergy and rational design of next-generation Cu-based methanol synthesis catalysts.

Palladium(II) complexes of the TPA family (TPA − tris(2-pyridylmethyl)amine) have recently emerged as efficient catalysts of highly 3°-regioselective hydroxylation and chemoselective 2°-ketonization of aliphatic C–H groups with peroxycarboxylic acids. Herewith, we present a novel facet of the catalytic reactivity of such complexes that have been shown to mediate highly efficient (at as low as 0.6 mol. % catalyst loadings) and selective trifluoroethoxylation of organic substrates at benzylic C–H groups, affording the corresponding trifluoroethoxy ethers in up to 73 % isolated yield. The developed synthetic protocol allows for diastereoselective trifluoroethoxylation of complex molecules of natural origin (steroids, terpenoids).

Anisole is a model molecule for studying hydrodeoxygenation (HDO) of lignin-derived oxygenates. Here we elucidate its HDO pathway over 10 % Ni/Al₂O₃ catalyst. Adsorption experiments showed that anisole is adsorbed on the acidic sites of the Al₂O₃. Anisole adsorption at 200–300 °C is reactive in nature, and results in its demethylation. The catalyst was tested at 100–300 °C, 5–40 bar H₂ pressure. Conversion of 78 % was obtained at 5 bar and 300 °C, restricted by hydrogenation-dehydrogenation equilibrium. HDO mainly starts through the ring-hydrogenation pathway. This is followed by demethoxylation beyond 180 °C. At 5–12 bar, cyclohexane dehydrogenates to benzene. This was confirmed by conducting an HDO experiment with methoxycyclohexane. At lower pressure deoxygenation is favored; and demethylation is accompanied with methylation of the aromatic ring, for temperature >260 °C. Investigation of the initial reaction stages showed that anisole HDO on Ni/Al₂O₃ catalyst proceeds via two independent pathways i.e., reactive adsorption/(de)methylation and  aromatic ring hydrogenation.

Hydrogenolysis of lignocellulose into renewable phenolic monomers through the reductive catalytic degradation (RCD) strategy is limited by cost and applicability, and there is a need to develop effective catalysts with controlled cost and greater applicability. Herein, we report the fabrication of CuO/CeO₂ catalyst toward RCD of lignocellulose for the production of monomeric phenols with different side chains. The catalyst can be adapted to softwoods (Larch and Pinus) and hardwoods (Eucalyptus and Poplar) with yields ranging from 8.8 % to 31.4 %, which afford certain monomer yields while controlling costs. Experimental results demonstrate that the acidic and basic sites of the CuO/CeO₂ catalyst assist the metal sites in the depolymerization of lignin. Notably, the mechanistic investigation reveal that the methoxylation process occurs on the aliphatic hydroxyl group. Moreover, the synergistic effects of hydrogen and catalyst exhibit high hydrogenolysis activity, which contributes to the efficient C − O bond scission, thus generating the target monomer products.

Investigating novel promoters and comprehending their roles is an important yet difficult task. In this study, we have introduced dual main-group single-atom In and P as co-promoters into the CuO surface lattice (In-P/CuO) via a straightforward hydrothermal CuO synthesis followed by impregnation. The In-P/CuO catalyst showed superior catalytic performance in dimethyldichlorosilane selectivity and yield to that of the pristine CuO and CuO with a single promoter in the important industrial Rochow-Müller reaction. The combination of thorough experimental characterization and density functional theory calculations reveals that the electron interaction between dual In and P promoters could optimize the local electronic structure of CuO and facilitate MeCl dissociation on the CuO surface, accelerating the transformation of CuO to Cu₂O, then CuCl, and eventually the active phase Cu₃Si and thereby enhancing overall activity. This work examines the synergistic interactions between dual main-group single-atom promoters in catalysts, offering a proven method for designing highly efficient catalysts.

Chain walking and chain transfer are pivotal processes that govern the microstructure and molecular weight of polyolefins synthesized via late transition metal-catalyzed ethylene (co)polymerization. In this study, we demonstrate that tailored metal–π interactions using heteroatomic dibenzosuberyl substituents can effectively modulate both chain transfer and chain walking in α-diimine nickel- and palladium-catalyzed systems. This modulation leads to significant reductions in the molecular weight and branching density of the resulting polyethylenes and copolymers. To achieve this, we designed, synthesized, and characterized a series of α-diimine Ni(II) and Pd(II) complexes bearing diverse heteroatomic dibenzosuberyl substituents. In nickel-catalyzed ethylene polymerization, the heteroatomic dibenzosuberyl Ni(II) catalysts showed lower catalytic activities and produced polyethylenes with fewer branches (21–48/1000C vs 83–90/1000C) and an order of magnitude lower molecular weight (2.3–6.5 kg/mol vs 54.6–89.1 kg/mol) than the non-heteroatomic dibenzosuberyl Ni(II) catalyst. Comparable trends were observed in palladium-catalyzed ethylene polymerization and ethylene-MA copolymerization, with sulfur-containing substituents exerting more pronounced effects. We propose a mechanism where the weak metal–π interactions between the dibenzosuberyl substituents and the metal center during polymerization catalysis suppress β-H elimination and promote synergistic chain transfer. This provides a rationale for the observed reductions in molecular weight and branching density, offering valuable insights for the rational design of catalysts for tailored polyolefin synthesis.

The limitation of isolated metal active sites in single atom catalysts (SAC) hinder their application in hydrogenation reactions, necessitating the creation of additional active site beyond the metal site. This study introduces pyridinic N and S atoms into the N/C sheet, optimally adjusting the local environment of the Co site. This adjustment synergistically enhances H₂ activation, H diffusion, and promotes the hydrogenation of nitrobenzene into aniline. The sterically hindered Co acidic site and N basic site, known as frustrated Lewis pairs, in defect-containing Co-N₃SN-def1 model cooperatively facilitate the highly efficient cleavage of the H₂ molecule with a barrier of only 0.37 eV. The findings suggest that the pyridinic N site in the Co-N₃SN-def1 model acts as a reservoir for *H, significantly contributing to the enhanced activity for the hydrogenation of nitrobenzene. The mechanism unveiled in this study offers valuable insights for designing efficient heterogeneous catalysts for target hydrogenation reactions.

The selective oxidation of methyl glycolate (MG) to methyl glyoxylate (MGO) using molecular oxygen in a fixed-bed reactor represents a greener and more efficient alternative to the traditional batch processing for producing this important fine chemical and intermediate. Despite its potential, detailed understanding of this catalytic reaction is still limited. In our study, VO_x/γ-Al₂O₃ catalysts were identified as effective for the reaction, but their performance strongly depended on the structure of VO_x species. The optimal catalyst with nearly monolayer dispersed VO_x achieved a high MG conversion of 91% and an MGO selectivity of 71%, alongside maintaining stability for 300 h without noticeable deactivation. At a low V loading of 0.6%, isolated VO_x species were formed, exhibiting the highest turnover frequency (TOF) but the lowest MGO selectivity. Increasing the V loading to 3.9% resulted in a blend of less polymeric and isolated VO_x species, which decreased the TOF but enhanced MGO selectivity to 59%. With the V loading ranging from 5% to 6.2%, monolayer dispersed VO_x became dominant, yielding a lower TOF and the highest MGO selectivity. A further increase in V loading caused the emergence of crystalline V₂O₅, which seemed to act as a bystander. Moreover, the redox cycles of V⁴⁺ and V⁵⁺ over the VO_x/γ-Al₂O₃ catalyst played an important role in the selective oxidation of MG to MGO, while the overoxidation of MG to CO₂ might take place through the V³⁺/V⁴⁺ redox pairs, the extent of which was determined by the structure of VO_x species. These insights are crucial for developing high-performance VO_x-based catalysts for the production of MGO through the selective oxidation of MG.

Selective CH₄ upgrading to C1 products and avoiding over oxidation remains a key challenge. Here, we develop a highly efficient Ni/CeO₂ nanorods containing both uniformly dispersed Ni-single-site and NiO_x/CeO₂ heterojunction for 100 % selectively CH₄ conversion to C1 products (CH₃OH, HCHO, CH₃OOH and HCOOH). Under optimized photocatalytic experimental conditions, a high C1 product yield of 5.6 mmol g^-1h⁻¹ was obtained with 100 % selectivity with presence of H₂O₂. Mechanism study showed that the Ni-single-site together with formed oxygen vacancy (O_v) facilitated CH₄ adsorption and activation. The terminal O atom of adsorbed ·OOH can fill the O_v, with the remaining *OH initiating *CH₃ dehydrogenation and forming *CH₂OH, which further reacts with ·OH to generate the main product HCHO. During the whole photocatalytic process, the formed NiO_x/CeO₂ heterojunction promoted carrier separation and enhanced catalytic performance.