ChemCatChem最新文献

Transition metal oxy-hydroxide (Ni, Fe, Co, Mo, and V)-decorated ITQ-2 composites were synthesized in-situ via controlled delamination of layered MCM-22(P) under optimized pH, generating highly accessible active sites with minimal diffusion limitations for biomass -derived molecules. The in-situ delamination strategy avoids multistep post-synthetic incorporation, ensuring maximum metal loading, strong anchoring, and structural integrity. Structural characterization confirmed nanosheet formation through the disappearance of the (002) interlayer reflection and broadening of intralayer reflections (220), (310)) in the X-ray diffraction (XRD) pattern and an increase in external surface area (90 to ∼300 m²/g) and mesopore volume (∼0.02 to 0.40 cm³/g) from N₂ sorption. Field emission scanning electron microscopy (FE-SEM) revealed a morphological transformation from stacked layers to dispersed platelets. The TEM/HR-TEM showed uniform slit like layers (∼2.5 nm) decorated with transition metal species (1.5–4 nm). XPS studies established the existence of Ni, Fe, and Co in +2 oxidation states, whereas V and Mo existed as V⁵⁺ and Mo⁶⁺ species, respectively. Catalytic studies demonstrated bifunctionality: ITQ-2-Ni-4 enabled complete hydrogenation of levulinic acid to γ-valerolactone (97% selectivity) via enhanced H₂ spillover and uniform Ni dispersion. ITQ-2-V-8 and ITQ-2-Fe-2 achieved > 85% conversion in iso-eugenol oxidation to vanillin through redox cycling and peroxo-species formation (> 90% selectivity). Though promising in activity, performance could be improved under continuous-flow vapor-phase conditions to mitigate coke deposition.

Pd was successfully encapsulated inside Silicalite-1 (S-1) using a ligand-assisted one-pot hydrothermal strategy. AC-TEM and XAFS characterizations confirmed that Pd species were confined in S-1 as highly dispersed metallic clusters with the size < 0.9 nm. The confinement effect of S-1 not only enhances the activity and C═O selectivity in the chemoselective hydrogenation of acetophenone, but also effectively inhibits Pd agglomeration and leaching. With L-proline serving as the chiral modifier in the enantioselective acetophenone hydrogenation, the Pd@S-1 catalyst exhibited a reaction rate and turnover frequency (TOF) of 60.6 mmol·h⁻¹·g_Pd⁻¹ and 14.4 h⁻¹, which are 36 and 29 times higher than those of the impregnated Pd/S-1 counterpart, respectively. The confinement effect of S-1 prevents excessive coverage of metal active sites by the chiral modifier, thereby enhancing both activity and enantioselectivity. A size-sieving effect was further demonstrated using chiral modifiers and acetophenone derivatives of different sizes. To validate the critical role of confinement, Pd@S-1@S-1 sample (core-shell) and hollow-Pd@S-1@S-1 sample (hollow-shell structure) were constructed by epitaxial growth of S-1 shell on the newly prepared or reduced Pd@S-1, respectively. As compared to Pd@S-1@S-1, the hollow-Pd@S-1@S-1 suffered from severe Pd aggregation and a sharp loss of activity due to the lack of pore confinement.

The oxygen evolution reaction (OER) leads to intrinsically sluggish kinetics, requiring a high overpotential and significantly limiting the overall water splitting energy conversion efficiency. Co-based catalysts have attracted considerable interest for the OER. Numerous studies have shown that trace Fe incorporation into Co-based catalysts enhances electrical conductivity and increases active site density, thereby improving OER performance. However, Fe-doped cobalt phosphates continue to encounter challenges, including intricate synthesis procedures, inadequate performance, and unclear mechanistic insights regarding the function of Fe. Herein, Fe-incorporated Co₃(PO₄)₂·8H₂O (FCPO) was successfully synthesized via a simple hydrothermal method. Notably, compared with Co-based phosphate electrocatalysts, the Fe incorporation modulates the electronic structure surrounding cobalt centers, facilitates cobalt valence transitions during OER. Besides, the exact location of Fe incorporation is determined through x-ray absorption and clarified the role of Fe in cobalt phosphate catalyst for OER. The material displays outstanding OER performance in 1.0 M KOH, requiring a low overpotential of 233 mV to achieve 100 mA cm⁻².

A novel chemoselective regulation was achieved through deliberate modulation of the reaction field. When Pd aggregates were employed in reactions with aryl bromides, Ullmann coupling occurring on the Pd surface proceeds selectively. In contrast, ppm-level Pd(OAc)₂ catalyzed hydrodebromination, which takes place in the homogeneous solution phase. Moreover, chemoselective discrimination between the Ullmann and Heck reactions was likewise realized through reaction-field control.

Selective activation of S═O and S─S bonds under mild conditions remains a fundamental challenge in sulfur chemistry. Herein, we report a nitrogen-doped molybdenum disulfide catalyst (N-MoS₂-9-500) synthesized via a ball-milling-assisted calcination method using trithiocyanuric acid as both sulfur and nitrogen sources. Comprehensive characterization by XRD, XPS, SEM, TEM, and Raman spectroscopy reveals that nitrogen doping induces abundant sulfur vacancies and expanded interlayer spacing, which are proposed to account for the active sites for H₂ activation and polar bond cleavage. The optimal catalyst exhibits high activity and selectivity for the hydrodeoxygenation (HDO) of a broad range of sulfoxides to the corresponding sulfides under mild conditions (60°C, 1.0 MPa H₂), and also shows good performance for the hydrogenation of various disulfides to thiols, with yields ranging from 97% to 99.9%. In addition, the catalyst exhibits stable catalytic performance and can be reused for at least five cycles without significant loss of activity in the HDO of methyl phenyl sulfoxide (MPSO) to methyl phenyl sulfide (MPS). This work provides a new non-precious metal catalytic platform for the sustainable and selective synthesis of sulfur-containing fine chemicals, highlighting the potential of defect-engineered MoS₂ catalysts in green catalysis.