ChemCatChem最新文献

Catalyst nanoparticles are dynamic, and their structures depend on the reaction conditions. Although average shapes can be observed experimentally, it is challenging to monitor transient structures and the mechanisms for structural changes during operating conditions. Herein, we use Density Functional Theory-based kinetic Monte Carlo simulations to study how CO affects adatom formation and clustering on Cu and Au surfaces and nanoparticles. Adatoms are created at undercoordinated sites and are stabilized by the formation of metal–CO complexes. Clusters of adatoms are formed on the (100) facets for both metals. The clusters are transient for Au, whereas they can be regarded as precursors for Cu nanoparticle reshaping. Bulk vacancies are present for Au, whereas vacancies are mainly located in the surface layer for Cu. The work demonstrates the structural flexibility of Au and Cu nanoparticles in the presence of an adsorbate, which has consequences for their catalytic properties.

Aldol condensation of vanillin and acetone is an efficient reaction for the synthesis of dehydrozingerone (DHZ). DHZ has been investigated for its potential pharmaceutical properties, which include multiple in vitro and in vivo studies related to its potential antioxidant, antibacterial, antiproliferative, antifungal, anti-inflammatory, antidiabetic, antimicrobial, and neuroprotective effects, among others. Recent research focused on the study of both pharmaceutical properties and synthesis processes. The use of strong alkaline media has been the traditional method for obtaining DHZ, leaving new open doors for the exploration of solid catalysts that facilitate its separation and allow its recycling, with the aim of obtaining high conversion, selectivity, and yield. The use of heterogeneous catalysts with strong acidity or basicity (Ni/Al₂O₃, Cu/Al₂O₃, hydrotalcites) stands out, allowing relatively moderate reaction conditions. This review summarizes recent advances in the exploration of new catalysts for obtaining DHZ by the aldol condensation reaction, reaction mechanism, alternative preparation methods (mechanochemistry), and use of reactors with microwave irradiation in combination with studies of their therapeutic properties.

Understanding the structure of semiconductor–electrolyte interfaces under operating conditions is crucial for designing electrodes in photoelectrochemistry and electrocatalysis. However, only few experimental methods exist that give real-time access to the very interface. Here, reflection anisotropy spectroscopy (RAS) is an emerging technique in the field of spectroelectrochemistry. We computationally investigate how the surface structure of clean and oxygenated InP(001) surfaces—in vacuum and in contact with water—and its evolution over time affect the optical response. Depending on the electronic structure of the respective surfaces, different species are adsorbed, resulting in changes of the anisotropy clearly visible in the spectroscopic fingerprint, while the presence of $$ stabilizes certain configurations. Distinct fluctuations of the individual spectra are observed during the molecular dynamics trajectory. However, the resulting time-averaged spectra show a rather good agreement with the respective spectra of the reference structure for most structures. This means that—depending on the surface—the geometry-optimized structures might be suitable for comparison with experiment or not. This behavior differs from the case of metals and can be attributed to the semiconducting nature of the system. Our findings highlight the need to account for the electrochemical environment in computational RAS.

Amine-impregnated mesoporous materials are studied for CO₂ sorption at conditions of direct air capture (DAC). Mesoporous silica supports with identical specific pore volume of 0.8 cm³ g⁻¹ but varying pore width (7 – 50 nm) were impregnated with polyethyleneimine (PEI) of different molecular mass (600 – 2000 g mol⁻¹) and loading (20 – 43 wt.-%). CO₂ adsorption was evaluated under dry conditions (450 ppm CO₂) across temperatures from 30 to 70°C, distinguishing the contributions of physisorption and chemisorption. The highest uptake of 1.19 mmol g⁻¹ was observed for sorbents with 30 nm pores and 33.3 wt.-% PEI loading at 50°C, balancing accessible amine density and free pore volume. A temperature-dependent shift from chemisorption to physisorption was identified, particularly in larger pores, where increased polymer mobility promotes enhanced physisorption of CO₂ via the “molecular basket” effect. Long-term cycling showed that narrow pores enhance stability by anchoring PEI through hydrogen bonding, especially for low-molecular-mass PEI. A kinetic model incorporating diffusion and surface reactions reproduces experimental trends across multiple temperatures and confirms that morphology, not intrinsic kinetics, governs CO₂ uptake. This provides mechanistic insight for designing improved sorbents for low-temperature CO₂ sorption under DAC conditions as well as catalysts for subsequent conversion to methanol.

Iron(II) triflate, Fe(OTf)₂ (OTf = CF₃SO₃⁻) has been used as a catalyst for directing group-free intermolecular C(sp³)─H fluorination in the absence of any added ligand. This transformation proceeds under mild conditions with low catalyst loading utilizing Selectfluor as the fluorine source. Reaction conditions were optimized, a range of substrates were evaluated, and the functional group tolerance of the fluorination strategy was systematically investigated. A plausible catalytic cycle is proposed based on the results of control experiments.

Ethylene is an established signaling molecule in plants and other organisms; however, the biosynthesis and biological roles of gaseous alkenes other than ethylene are less well defined. The Pseudomonas savastanoi ethylene/succinate-forming enzyme (PsEFE) catalyzes ethylene production from 2-oxoglutarate (2OG), though does not catalyze formation of alkenes from C4 alkyl- or hydroxyl-substituted 2OG derivatives. Here we report studies on the reactivity of L206 PsEFE variants with C4-substituted 2OG derivatives. Spectroscopic evidence reveals that L206V and L206A PsEFE react with C4-substituted 2OG derivatives to give diacid and alcohol products, similarly to wildtype (wt) PsEFE. Importantly, L206V PsEFE, but not L206A and L206G PsEFE, catalyzed production of low levels of acetaldehyde and propylene from the natural metabolites 4-hydroxy-2OG and 4-methyl-2OG, respectively. By contrast, L206A PsEFE, but not L206V and L206G PsEFE, catalyzed formation of low levels of 1-butylene from 4-ethyl-2OG. Together with studies from others, the combined results indicate the potential of bump-and-hole studies to modify the substrate and product selectivities of PsEFE reactions, provided that the PsEFE variant:2OG derivative pairs are matched. The results suggest that wildtype 2OG oxygenases other than PsEFE may catalyze production of gaseous alkenes other than ethylene.