ChemSusChem最新文献

pKa values of C-H bonds remain unreported and challenging in fluorous solvents because of these solvents' unique physicochemical properties, although they have been measured, theorized and predicted successfully in water and common organic solvents. Herein, a new CF3SO2-substituted anchor compound designed for matching the physicochemical properties of polar fluorinated arenes is synthesized. Its self-dissociation constants in these solvents are used as bases for experimentally determining the pKa values of 36 C-H compounds in them. These experimentally determined pKa values exhibit excellent linear free-energy relationships and correlate well with their corresponding DFT-calculated values. These data indicate that the polar fluorinated arenes are thermodynamically more favorable for deprotonation of ketone derivatives than acetonitrile as reaction media, resulting in enhanced deprotonation-promoted CO2 fixation. The pKa values determined in this work can be used as an important guidance tool for reactions involving the formation and cleavage of C-H bonds in polar fluorinated arenes.

An efficient Ni-based heterogeneous catalyst from pine needles urban waste valorization was designed and developed with a resource recycling strategy. The Ni/PiNe catalyst was fully characterized and tested in the Suzuki-Miyaura coupling under microwave irradiation. Although Ni is a promising candidate for replacing Pd-based catalytic systems, it generally requires a high catalyst amount and the exploitation of ligands and additives to enhance the reaction rate. On the contrary, with our new Ni/PiNe, 30 different products were efficiently synthesized with an isolated yield of up to 93%, using a very low catalyst amount and in the absence of ligands. Furthermore, the Ni/PiNe catalyst also showed good durability for consecutive cycles and an impressive TON value (1140). In addition to the catalytic efficiency in short reaction time and to the stability and durability under MW irradiation, the Ni/PiNe allowed for further optimization, achieving a low E-factor value (14.0), thus highlighting the potential in further reducing the waste and costs associated to the process.

Si-based anodes can increase specific energy and energy density of Li ion batteries. However, the volume-induced material stress and capacity loss necessitates only a partial Si utilization within composite anodes, typically with state-of-the-art graphite, so called Si/Gr composites. In this work, various Si nanowires (SiNWs), a promising Si architecture for these composites, are investigated and modified via pre-lithiation. Though, charged pre-lithiated anodes show potentials below 0 V vs. Li|Li+ in the initial cycles, they do not show indications for metallic Li, which is likely a hint for a triggered surface Li depletion in course of a continuous "transfer-lithiation" from lithiated Gr to Si, which is indicated by decreasing LiC6 and increasing LixSiy signals via nuclear magnetic resonance (NMR), X-ray diffraction (XRD) as well as shifts in capacities of respective voltage plateaus during discharge after storage. A relevant contribution of self-discharge is unlikely as shown by a stable open-circuit-voltage during storage in charged state and similar subsequent discharge capacities, being consequently also a hint for an intra-electrode capacity shift. The process of transfer lithiation is finally validated via solid-state 7Li NMR for varied Si morphology, i.e., amorphous and crystalline, as well as during pre-lithiation with passivated lithium metal powder (PLMP).

Surface-like diffusion is a recently proposed concept to explain the mechanism of ultrafast ionic conduction in high-rate oxide (e. g., niobium oxides and their alloys with TiO₂ and WO₃) and framework materials (e. g., Prussian blue analogs). This perspective seeks to illustrate the structural origin, theoretical foundation, and experimental evidences of surface-like diffusion. Unlike classical lattice diffusion, which typically involves ionic hopping between adjacent interstitial sites in solids, surface-like diffusion occurs when ions-that are significantly smaller than the interstitials-migrate along the off-center path in the diffusion channel. This mechanism results in an exceptionally low activation energy (E_a) down to 0.2 eV, which is crucial for achieving high-rate performance in electrochemical devices such as lithium-ion and sodium-ion batteries. This concept review also discusses the criteria to identify materials with potential surface-like diffusion and outlines theoretical and experimental tools to capture such phenomenon. Several candidates for further investigation are proposed based on the current understanding of the mechanism.

The electrochemical reduction of nitrate to ammonia presents a promising alternative to the conventional Haber-Bosch process. In this study, a bimetallic NiCo alloy embedded in metal-organic framework derived carbon layer with B doping electrocatalyst NiCo@BC was first successfully developed, which exhibits excellent electrochemical nitrate reduction to ammonia (ENO3RR) performance. In-depth in situ experiments and a machine-learning potential (MLP)-based simulation reveal that B doping within the carbon layer has a crucial anchor effect that induces strong binding between bimetal NiCo alloy and carbon support. Moreover, B doping leads to a decrease in the coordination numbers around the metals, which results in a reduction of the excessively strong intermediates adsorption in the ENO3RR process, thereby significantly enhancing catalytic activity. The fabrication strategy of this electrocatalyst provides a new avenue on ENO3RR research.

The development of efficient and sustainable chemical processes which use greener reagents and solvents, currently play an important role in current research. Methanol, a cheap and readily available resource from chemical industry, could be activated by transition metal catalysts. This review focuses in covering the recent five-years literature and provides a systematic summary of strategies for methanol activation and the use in organic chemistry. Based on these strategies, many new synthetic methods have been developed for methanol utilization as the C1 building block in methylation, hydromethylation, aminomethylation, formylation reactions, as well as the syntheses of urea derivatives and heterocycles. The achievements, synthetic applications, limitations, some advanced approaches, and future perspectives of the methanol activation methodologies have been described in this review.

The orbital modulation and surface lattice reconstruction represent an effective strategy to regulate the interaction between catalyst interface sites and intermediates, thereby enhancing catalytic activity and selectivity. In this study, the crystal surface of Au-K/CeO2 catalyst can undergo reversible transformation by tuning the coordination environment of Ce, which enables the activation of the Cβ-H bond and the oxidative cleavage of the Cβ-O and Cα-Cβ bonds, leading to the  cleavage of 2-phenoxy-1-phenylethanol. The t2g orbitals of Au 5d hybridize with the 2p orbitals of lattice oxygen in CeO2 via π-coordination, modulating the coordination environment of Ce 4f and reconstructing the lattice oxygen in the CeO2 framework, as well as increasing the oxygen vacancies. The interface sites formed by the synergy between Au clusters in the reconstructed Ce-OL1-Au structure and doped K play dual roles. On the one hand, it activates the Cβ-H bond, facilitating the enolization of the pre-oxidized 2-phenoxy-1-phenylethanone. On the other hand, through single-electron transfer involving Ce3+ 4f1 and the adsorption by oxygen vacancies, it enhances the oxidative cleavage of the Cβ-O and Cα-Cβ bonds. This study elucidates the complex mechanistic roles of the structure and properties of Au-K/CeO2 catalyst in the selective catalytic oxidation of lignin β-O-4 bond.

The acetosolv extraction, allylation and subsequent cross-linking of wheat straw lignin to thermoset biomaterials is herein described. The extraction temperature proved to be of great importance for the quality of the resulting lignin, with moderate temperature being key for preservation of β-O-4' linkages. The allylation of the acetosolv lignin was carried out using three different synthetic strategies, resulting in selective installation of either benzylic or phenolic allyl ethers, or unselective allylation of various hydroxyl groups via etherification and carboxyallylation. The different allylation protocols employed either allyl alcohol, allyl chloride, or diallylcarbonate as allyl precursors where the latter gave the highest degree of functionality. The results also show that it is crucial to choose a functionalization protocol that is adapted to the functional groups present in the specific lignin used. Selected allylated acetosolv lignins were cross-linked using a thiol-ene approach and the lignin with the highest density of allyl groups was found to form a cross-linked thermoset material with properties comparable to kraft lignin-based analogues.

Advancing the use of air-sensitive polar organometallic Grignard and organolithium reagents under more environmentally benign conditions, here we report the addition of these reagents to a-b unsaturated ketones and aldehydes using the deep eutetic solvent (DES) choline chloride (ChCl): glycerol (Gly) (1:2), under air. Reactions occur at room temperature within seconds with excellent regioselective control. Furthering understanding of how these C-C bond forming processes take place in these reaction media, we have explored the surface concentration of the organic substrate (chalcone) in DES using interfacial tension and neutron reflectivity measurements, finding that chalcone is concentrated at the DES-hydrocarbon interface compared to the bulk concentration, although the interfacial chalcone concentration is still relatively low in this system. The influence of aggregation of the organometallic reagent in the organic solvent employed has also been evaluated, revealing the importance of achieving a balance between activation (via de-aggregation) and stability (to avoid its decomposition in the DES). This DES approach has been successfully extended to double additions to a-b unsaturated estes and for one pot sequential 1,4 and 1,2 additions to ketones, providing a new entry point to a range of tertiary-alcohols, minimising the use of organic solvents and avoiding intermediate time-consuming purification steps.

In recent years, the electrochemical reduction of carbon dioxide (CO2RR) has made many advances in C2+ production. Cu+/Cu0 site is beneficial for C-C coupling process, but the oxidation state of copper cannot be well maintained during the reaction process, resulting in a decrease in catalyst activity. Based on this consideration, in this work, transition metal oxide CeO2 with a hollow cube structure and oxygen vacancies was introduced to stabilize and increase Cu+/Cu0 active sites (Ce1Cu2). The catalyst exhibits excellent CO2RR performance, with FEC2+ achieving 73.52% and jC2+ > 280 mA/cm2 at 1.26 V (vs. RHE). Ethanol is the main C2+ product and FEethanol reaches 39% at 1.26 V. The experimental results indicate that the presence of CeO2 provides a large number of oxygen vacancies and forming Cu+-O2--Ce4+ structure by the strong interaction of CeO2 and Cu NPs. The structure of Cu+-O2--Ce4+ and abundant oxygen vacancies lay a good foundation for the CO2 adsorption. Moreover, it increases the content of Cu+/Cu0 sites, effectively inhibiting hydrogen evolution reaction, promoting the C-C coupling interaction, thereby facilitating the generation of C2+ products. The DFT theoretical calculation further demonstrates that Ce1Cu2 is more inclined towards the ethanol pathway, confirming its high selectivity for ethanol.