ChemCatChem最新文献

The electrochemical CO₂ reduction reaction (CO₂RR) to carbon monoxide (CO) offers a promising strategy for mitigating global warming while providing a valuable industrial feedstock. Polyoxometalates (POMs), anionic metal–oxo clusters, are attractive precursors for CO₂RR catalysts owing to their structural and compositional tunability, as well as their versatility of their countercations. However, POM-based CO₂RR catalysts often exhibit limited activity and require high overpotentials. Herein, we report a high performance CO₂RR nanocatalyst derived from a Ba²⁺ salt of an Au–Ag alloy nanocluster incorporated in a POM framework, [Au₈Ag₂₆(P₈W₄₈O₁₈₄)]²⁴⁻ (AuAg), supported on a carbon black (Ba-AuAg/C). This system achieves a high current density (171 ± 4 mA cm⁻²) and Faradaic efficiency (95.3 ± 4.2%) for CO production at a low overpotential (−0.39 V_RHE), outperforming previously reported POM-based CO₂RR catalysts. Postreaction analyses reveal the transformation of Ba-AuAg/C into small Au–Ag alloy nanoparticles with uniform elemental distribution, along with WO_x nanoaggregates. Control experiments and detailed characterizations highlight the critical roles of the constituent elements, countercations, and catalyst structure in achieving superior catalytic performance. This work provides a new design strategy for the development of highly efficient and selective POM-based nanocatalysts for electrochemical CO₂ conversion.

The β-hydroxysulfide motif is present in both natural and synthetic compounds with notable bioactivities. Herein, the synthesis of a set of optically active (R)- and (S)-β-hydroxysulfides starting from β-ketosulfides using ketoreductases (KREDs) in nonconventional media aqueous buffer/deep eutectic solvents (DESs) has been developed. Several Type III DESs have been tested as cosolvents, being observed for most of the biotransformations higher conversions and enantiomeric excesses in the presence of some glycerol- or ethylenglycol-based DESs. Bioreductions can be performed up to 70% v/v of DESs with good conversions, demonstrating the high performance of these nonconventional media in biocatalyzed reductive processes. Additionally, it was observed that the lipase CalB partially retained activity in DES-containing media for the hydrolysis of β-alkylsulfide enol esters, thus being possible to develop a one-pot, two-enzyme cascade that combined CaalB-catalyzed hydrolysis of a β-alkylsulfide enol ester with the subsequent KRED reduction of the β-ketosulfide obtained to the (R)-β-hydroxysulfide in both sequential and concurrent ways, affording high stereoselectivity.

The redox interactions between transition metal oxides and sulfur-containing compounds play a key role in catalytic processes and gas sensing technologies. In this study, we investigated the redox dynamics of Co₃O₄(111)/Ir(100) model catalysts in response to the adsorption and decomposition of hydrogen sulfide (H₂S) using synchrotron radiation photoelectron spectroscopy. Upon adsorption at 300 K, H₂S partially dissociates to form a mixture of SO₃²⁻, S²⁻, OH⁻, SH⁻, and chemisorbed H₂S. Subsequent annealing in ultrahigh vacuum induces H₂ desorption below 400 K followed by desorption of H₂S and H₂O above 400 K. At temperatures exceeding 500 K, S²⁻ is progressively oxidized to SO₃²⁻ and subsequently to SO₄²⁻. These transformations are accompanied by temperature-dependent redox processes involving the Co₃O₄(111) surface: initial reduction upon formation of SO₃²⁻ species at 300 K, partial re-oxidation upon H₂ desorption, and further reduction with H₂O release. Above 550 K, annealing induces charge redistribution and lattice oxygen migration, leading to a more homogeneous stoichiometry of the Co₃O₄(111) film. This phenomenon reduces the redox response to chemical transformations at the surface. The obtained insights into H₂S–Co₃O₄ redox interactions provide a foundation for the rational design of cobalt oxide-based catalytic gas sensors.

The catalytic conversion of biomass-derived sugars to 5-hydroxymethylfurfural (5-HMF) over zeolites is challenging due to internal mass transfer limitations arising from their microporous framework. To overcome this chronic issue, we prepared a set of micro-mesoporous zeolites (22 samples), whose properties were fully characterized in our previous study using XRD, XRF, N₂ Physisorption, IR with pyridine and tri-tert-butylpydirine, and ²⁷Al NMR. In this study, we aim to investigate how highly correlated zeolite properties, such as textural and acidic characteristics, influence fructose dehydration to 5-HMF, and to identify the key properties that govern the catalyst efficiency for sugar conversion. Since simple correlations of catalytic activity with individual descriptors of texture and acidity could not be found, we employed a chemometric approach, by using a combination of principal component analysis (PCA) and multiple linear regression (MLR). PCA was used to visualize the relationship between properties and catalyst performance, and to reduce redundant features for the subsequent MLR model, which was developed to correlate selected catalyst properties with 5-HMF yield. The model shows strong predictive performance, with randomly scattered residuals around zero. The property activity relationships reveal that preservation of the crystalline framework and enhancement of active sites accessibility are the key factors for improving catalytic performance for sugar conversion. However, this remains valid under the condition that excessive amorphization and related Lewis acidity are minimized. This study demonstrates that chemometrics is effective for analyzing property-activity relationships in a set of zeolites when these relationships are complex and highly correlated.

Biomass-derived levulinic acid and furfural are promising alternatives to traditional fossil-fuel-based raw materials for applications such as biofuels, biosolvents, resins, and bioplastics. In this work, we present the synthesis and characterization of highly reactive compounds that have been reported previously but remain unexplored in biomass valorization: diphosphine cobalt (I) complexes of the type [(diphosphine)CoPPh₃Cl]. These complexes are closely related to reported copper (I) and palladium (II) complexes, which have been successfully used in levulinic acid hydrogenation under impressive reaction conditions. These complexes were synthesized using commercially available, low-cost precursors and feature bidentate ligands with different bite angles and electronic and steric parameters. We applied these cobalt complexes in the direct hydrogenation of levulinic acid and furfural to produce selectively gamma-valerolactone (total conversion at 120°C and H₂ 300 psi, 99% yield) and tetrahydrofurfuryl alcohol (total conversion at 100°C and H₂ 300 psi, 98% yield), respectively, using relatively mild reaction conditions, among the mildest for nonnoble metals systems and through the in situ formation of cobalt nanoparticles which allows a high dispersion and TOFs of 41.7 for both system at its respective optimal conditions.

The influence of vanadium surface density and support nature (MoO₃, Nb₂O₅, and SiO₂) on V₂O₅-supported catalysts was systematically investigated for the CO₂-assisted oxidative dehydrogenation of propane (CO₂-ODHP). Two catalyst series were prepared: one with a fixed V₂O₅ loading (5 wt.%), leading to high vanadium surface densities, and another targeted to a theoretical density of 2 V.nm⁻², corresponding to highly dispersed species. The materials were characterized by XRD, N₂ physisorption, ED-XRF, H₂-TPR, UV-vis, and in situ Raman spectroscopy. Structural analyses revealed that high vanadium densities favored the aggregation into polymeric domains and clusters, whereas lower densities stabilized isolated and oligomeric VO₄ species. Catalytic tests showed that these isolated/oligomeric species were the most active for CO₂-ODHP, with those supported on MoO₃ and Nb₂O₅ exhibiting the highest propylene-specific activities due to strong VO_X-support interactions. Notably, the highly dispersed VO_x species on MoO₃ exhibited the best overall performance, owing not only to the presence of monomeric and polymeric vanadium domains but also to the intrinsic activity of MoO_x sites. Indeed, in this catalyst, CO₂ can effectively reoxidize V─O_v─V and V─O_v─Mo interfaces, as well as V═O terminal oxygen sites, through the rWGS reaction, thereby improving catalytic stability and preventing coke formation.