Reactive Intermediates Research Articles

Dynamically Reconstructed Fe-CoOOH Semi-Crystalline Electrocatalyst for Efficient Oxygen Evolution Reaction.

The development of robust and efficient electrocatalysts for the oxygen evolution reaction (OER) has been the main focus of water electrolysis but remains a great challenge. Here, the synthesis of a highly active and ultra-stable Fe-CoOOH electrocatalyst is reported by steering raw cobalt foam via an in situ solution combustion method assisted by a galvanic replacement reaction and subsequent electrochemical reconstruction of the CoFeOx pre-catalyst. In/ex situ electrochemical analysis and physicochemical characterizations show that the CoFeOx undergoes quick chemical and slow morphological reconstruction to Fe-CoOOH nanosheets. The Fe-CoOOH possesses a semi-crystalline nature with distinct short-range ordering and outstanding OER activity with overpotentials as low as 271 and 291mV at current densities of 500 and 1,000mAcm-2, respectively. The remarkable stability under 1,000mAcm-2 for at least 700 h is achieved. Theoretical calculations confirm the crucial role of Fe doping in facilitating surface reconstruction, enhancing OER activity, and improving the stability of the Fe-CoOOH. Comparative analysis with other transition metals doping reveals the unique ability of Fe to adsorb onto the CoOOH surface, thereby modulating the electronic density and facilitating faster adsorption of reaction intermediates. This work represents valuable insights into the surface reconstruction and doping processes.

A Tool for Reaction Monitoring in Real Time, the Development of a "Walk-Up Automated Reaction Profiling" System.

Optimization of chemical reactions requires a thorough analysis of reaction products and intermediates over a given time course. Chemical reactions are often analyzed by liquid chromatography-mass spectrometry (LC-MS), but generating LC-MS samples and data analysis is time-consuming and produces a significant amount of waste. We sought to remove the sample preparation and data analysis steps by implementing an iChemExplorer/Agilent LC-MS instrument as our reactor and analysis tool, coupled with an automated report generator of reaction progress over time. Herein, we show that our easy-to-use walk-up automated reaction profiling (WARP) system can sample chemical reactions multiple times to produce a data-rich report of reaction progress over time.

Mesoporous Cu-doped ZSM-5 zeolite for efficient radical-mediated decarboxylative silylation

Vinylsilane compounds are essential chemical feedstocks and intermediates in organic synthesis. A heterogeneous Cu-containing mesoporous ZSM-5 zeolite catalyst developed through an in-situ doping method can be used for preparing vinylsilane compounds via decarboxylative coupling with remarkable catalytic efficiency. The mesoporous structure along with the appropriate surface area and pore volume of the catalyst is likely to be responsible for facilitating mass transfer in the reaction process. Additionally, due to the suitable Brønsted and Lewis acid active sites, adsorption and activation of reactant molecules can be readily triggered to promote the generation of alkoxyl radicals, which is the crucial species to complete the catalytic cycle. Importantly, the transformation exhibits high efficiency, broad substrate scope, and good reusability for at least six cycles.

High-throughput screening of a transition metal single-atom electrocatalyst for the CH3NO2 reduction reaction

The hydrogenation reduction of nitro compounds involves the wide application of functional amines as important chemical intermediates in the fine chemical industry. However, the development of low-cost, mild reaction conditions and high-performance catalysts for the reduction of nitro compounds is challenging. In this study, the potential of electrocatalysts in which 26 transition metal atoms are anchored to the surface of N-doped graphene (TMN4@G) was explored to determine the mechanism of the electrocatalytic CH3NO2 reduction reaction (CNORR) via density functional theory. First, the stability of TMN4@G was evaluated to screen out the catalyst which is stable at 300 K via ab initio molecular dynamics. Second, the Gibbs free energy with all possible reaction pathways of the CNORR was calculated to search for high-performance catalysts. These results demonstrate that monodentate adsorbed CdN4@G, FeN4@G, CoN4@G and bidentate adsorbed MoN4@G exhibit excellent catalytic activity. The overpotential of MoN4@G is only 0.357 V. Finally, Finally, the role of central metal atom on the catalytic activity of single-atom catalysts in CNORR and the impact of hydrogen evolution reaction on the adsorption of CH3NO2 were further discussed. We hope that this theoretical simulation provides an effective scheme for the reduction of nitro compounds under mild conditions.

Molecular Complexity-Inspired Synthetic Strategies toward the Calyciphylline A-Type Daphniphyllum Alkaloids Himalensine A and Daphenylline.

In this report, we detail two distinct synthetic approaches to calyciphylline A-type Daphniphyllum alkaloids himalensine A and daphenylline, which are inspired by our analysis of the structural complexity of these compounds. Using MolComplex, a Python-based web application that we have developed, we quantified the structural complexity of all possible precursors resulting from one-bond retrosynthetic disconnections. This led to the identification of transannular bonds as especially simplifying to the molecular graph, and, based on this analysis, we pursued a total synthesis of himalensine A from macrocyclic intermediates with planned late-stage transannular ring formations. Despite initial setbacks in accessing an originally designed macrocycle, targeting a simplified macrocycle ultimately enabled investigation of this intermediate's unique transannular reactivity. Given the lack of success to access himalensine A based solely on molecular graph analysis, we revised our approach to the related alkaloid, daphenylline. Herein, we also provide the details of the various synthetic challenges that we encountered and overcame en route to a total synthesis of daphenylline. First, optimization of a Rh-mediated intramolecular Buchner/6π-electrocyclic ring-opening sequence enabled construction of the pentacyclic core. We then describe various attempts to install a key quaternary methyl group and, ultimately, our solution to leverage a [2 + 2] photocycloaddition/bond cleavage sequence to achieve this elusive goal. Finally, a late-stage Friedel-Crafts cyclization and deoxygenation facilitated the 11-step total synthesis, which was made formally enantioselective by a Rh-mediated dihydropyridone conjugate arylation. Complexity analysis of the daphenylline synthesis highlights how complexity-building/C-C cleavage combinations can be uniquely effective in achieving synthetic outcomes.

Uniform anchoring of MoS2 nanosheets on MOFs-derived CoFe2O4 porous nanolayers to construct heterogeneous structural configurations for efficient and stable overall water splitting

Rational interfacial engineering and morphology modulation are recognized as effective strategies to modulate the electronic structure and improving the activity of spinel materials. In this paper, we report a strategy of Fe-induced creation of porous nanolayers of CoFe2O4 with unique morphology derived from MOFs by introducing ferrocene, and then constructed CoFe2O4/MoS2 heterostructures were fabricated by homogeneously anchoring MoS2 nanosheets onto the surface of CoFe2O4. The triple synergistic effect of heterogeneous interfaces, highly active Mo(IV) sites, and unsaturated S effectively accelerates the cycling process between Fe(III)/Fe(II) and Co(III)/Co(II), which in turn enhances the adsorption of reactive intermediates on the active sites, as further corroborates by density functional theory (DFT) calculations. As a result, the CoFe2O4/MoS2 heterostructured catalysts prepared without noble metals exhibit high catalytic performance, necessitating only 270 mV and 229 mV to achieve the current density of 100 mA·cm−2 for OER and HER respectively, which is superior to most of the reported catalysts of interest. In addition, when used in an alkaline electrolyzer, it provides a current density of 10 mA·cm−2 at 1.54 V cell voltage. This work provides a new way for the rational construction of bifunctional water electrolytic catalysts.

Rhodium-Catalyzed Asymmetric Reductive Hydroformylation of α-Substituted Enamides.

Chiral γ-amino alcohols are prevalent structural motifs in natural products and bioactive compounds. Nevertheless, efficient and atom-economical synthetic methods toward enantiomerically enriched γ-amino alcohols are still lacking. In this study, a highly enantioselective rhodium-catalyzed reductive hydroformylation of readily available α-substituted enamides is developed, providing a series of pharmaceutically valuable chiral 1,3-amino alcohols in good yields and excellent enantioselectivities in a single step. The development of the 4,4'-bisarylamino-substituted BIBOP ligand is crucial for the success of this transformation. DFT calculations and experimental data have revealed the importance of hydrogen bonding between the N-H group in the structure of TFPNH-BIBOP and the enamide carbonyl group in promoting both high enantioselectivity and reactivity. This method has enabled the concise synthesis of several chiral pharmaceutical intermediates including a single-step synthesis of the key chiral intermediate of maraviroc.

Exploring Thermocatalytic Pyrolysis to Derive Sustainable Chemical Intermediates from Plastic Waste; Role of Temperature, Catalyst, and Reactor Conditions

Exploring Thermocatalytic Pyrolysis to Derive Sustainable Chemical Intermediates from Plastic Waste; Role of Temperature, Catalyst, and Reactor Conditions

Dynamic Reconstruction of Cu Catalyst Under Electrochemical NO Reduction to NH3.

The electrochemical reduction of nitric oxide (NO) to ammonia (NH3) offers a sustainable way of simultaneously treating the air pollutant and producing a useful chemical. Among catalyst candidates, Cu emerges as a stand-out choice for its superb NH3 selectivity and production rate. However, a comprehensive study concerning its catalytic behavior in the NO reduction environment is still lacking. Here, we unravel the dynamic rearrangement of Cu catalysts during NO reduction: the emergence of a bundled nanowire structure dependent on the applied potential. This unique structure is closely linked to an enhancement in double-layer capacitance, leading to a progressive increase in current density from 236 mA cm-2 by 20 % over 1 h, while maintaining a Faradaic efficiency of 95 % for NH3. Characterizations of Cu oxidation states suggest that the nanostructure results from the dissolution-redeposition of Cu in the aqueous electrolyte, influenced by the interaction with NO or other reactive intermediates. This understanding contributes to the broader exploration of Cu-based catalysts for sustainable and efficient NH3 synthesis from NO.

ESTUDO DE PARTICULAS DE ZnO PURO E DOPADO COM Ag APLICADO NA DEGRADAÇÃO DA CAFEÍNA: INFLUÊNCIA DO PH

Caffeine, when detected in drinking water and surface water, is classified as a contaminant of emerging concern. This designation includes substances whose effects on living beings are little known, and there is no legislation that sets a maximum discharge limit. Heterogeneous photocatalysis has proven to be a technique capable of degrading organic compounds through the formation of reactive intermediates. Some of the factors that influence the photocatalytic reaction are pH, a parameter that can alter the surface of the catalyst, whether or not this change is favorable for the adsorption of pollutant molecules and subsequent photocatalytic reaction. This research evaluated the influence of pH on the photocatalytic degradation of caffeine using pure ZnO and 5% Ag as a catalyst. It was possible to verify that, in general, in a basic reaction medium the kinetics of degradation of the pollutant were superior in relation to the acidic medium, however, for the three different pH values, at the end of the reaction the degradation of caffeine was above 98% for both catalysts.

Insight Into Intermediate Behaviors and Design Strategies of Platinum Group Metal-Based Alkaline Hydrogen Oxidation Catalysts.

Hydrogen oxidation reaction (HOR) can effectively convert the hydrogen energy through the hydrogen fuel cells, which plays an increasingly important role in the renewable hydrogen cycle. Nevertheless, when the electrolyte pH changes from acid to base, even with platinum group metal (PGM) catalysts, the HOR kinetics declines with several orders of magnitude. More critically, the pivotal role of reaction intermediates and interfacial environment during intermediate behaviors on alkaline HOR remains controversial. Therefore, exploring the exceptional PGM-based alkaline HOR electrocatalysts and identifying the reaction mechanism are indispensable for promoting the commercial development of hydrogen fuel cells. Consequently, the fundamental understanding of the HOR mechanism is first introduced, with emphases on the adsorption/desorption process of distinct reactive intermediates and the interfacial structure during catalytic process. Subsequently, with the guidance of reaction mechanism, the latest advances in the rational design of advanced PGM-based (Pt, Pd, Ir, Ru, Rh-based) alkaline HOR catalysts are discussed, focusing on the correlation between the intermediate behaviors and the electrocatalytic performance. Finally, given that the challenges standing in the development of the alkaline HOR, the prospect for the rational catalysts design and thorough mechanism investigation towards alkaline HOR are emphatically proposed.

Carbon Dots Boost the Electrocatalytic Ammonia Oxidation Reaction on Pt2Pd Nanosheet

AbstractThe development of efficient catalysts for high‐performance ammonia oxidation reaction (AOR) is crucial for direct ammonia fuel cells. However, AOR is severely affected by slow kinetics and the toxicity of reaction intermediates, which reduce the durability of precious metal catalysts. Here, a two‐dimensional carbon dots modified Pt2Pd nanoporous alloy (Pt2Pd‐CDs) is synthesized through the borane morpholine reduction of a platinum palladium oxide nanosheet. The Pt2Pd_3 % CDs (the mass of CDs is 3 % of Pt2Pd) exhibits high AOR activity and stability in alkaline media, with an onset potential of 0.41 V vs. RHE, which is 170 mV lower than that of the commercial Pt/C (0.58 V vs. RHE). In addition, after 2000 cycles of accelerated durability testing, the peak mass activity (115.3 A gPGM−1) decreases by only 25.8 %. This enhancement is mainly attributed to the unique advantage of two‐dimensional nanoporous structure with a high electrochemical surface area, and the strong ammonia adsorption and the electron deliver capacity of CDs.

Variation in photoactivity of dissolved black carbon during the fractionation process and the role in the photodegradation of various antibiotics

The composition of dissolved black carbon (DBC) could be influenced by adsorption on minerals, subsequently affecting DBC’s photoactivity and the photoconversion of contaminants. This study investigated the changes in photoactivity of DBC after absorption on ferrihydrite at Fe/C ratios of 0, 1.75, 7.50, and 11.25, compared the influences of DBC0 and DBC7.50 on the photodegradation of four typical antibiotics (AB) including sulfadiazine, tetracycline, ofloxacin, and chloramphenicol. The selective adsorption led to the compounds with high aromaticity, high oxidation states, and more oxygen-containing functional groups being more favorably adsorbed on ferrihydrite, further causing the steady-state concentrations of 3DBC*, 1O2, and •OH respectively to drop from 1.83 × 10−13 M, 7.45 × 10−13 M, and 3.32 × 10−16 M in DBC0 to 1.22 × 10−13 M, 0.93 × 10−13 M and 2.30 × 10−16 M in DBC11.25, while the light screening effect factor increased from 0.740–0.921 in DBC0 with above four antibiotics to 0.775–0.970 for that of DBC11.25. Unexpectedly, DBC after adsorption played a dual role in the photodegradation of various antibiotics. This difference might be caused by antibiotics’ chemical composition, functional groups interacting with reactive intermediates, and the overlap in UV–vis spectra between antibiotics and DBC. Our data are valuable for understanding the dynamic roles of DBC in the photodegradation of antibiotics.

Developing Schottky high-controductivity Ti3C2TX MXene/Ni2P/NF heterojunction with modulating surface electron density to boost hydrogen evolution reaction

Nickel-based transition metal electrocatalysts for water electrolysis are promising alternatives to precious metal based electrocatalysts, due to their high activity, low cost, and relatively high stability, offering broad prospects for application in hydrogen production via water electrolysis. Modifying nickel-based transition metal electrocatalysts with phosphorus elements and Schottky heterojunction interfaces can influence the electronic state of the metal, thus enhance the electrocatalytic performance of the catalyst. In this study, a phosphor modified nickel-based electrocatalyst, i.e. MXene/Ni2P/NF electrode material was obtained by assembling Ni2P nanosheets on a nickel foam (NF) substrate and then depositing MXene nanosheets onto the surface of Ni2P/NF via electrophoretic deposition. Water droplets can wet the interior of the electrode material within 150 ms (below the detection limit), demonstrating excellent hydrophilicity, which facilitates the wettability of the electrolyte and the adsorption/desorption of reaction intermediates. Electrochemical tests revealed that the MXene/Ni2P/NF electrode exhibits an overpotential of only 94 mV at a current density of 10 mA cm−2, with a Tafel slope of 83.7 mV dec−1, in the hydrogen evolution reaction. The overpotential remains virtually unchanged after a 24-h stability test.

Engineering a Cu-Pd Paddle-Wheel Metal-Organic Framework for Selective CO2 Electroreduction.

Optimizing the binding energy between the intermediate and the active site is a key factor for tuning catalytic product selectivity and activity in the electrochemical carbon dioxide reduction reaction. Copper active sites are known to reduce CO2 to hydrocarbons and oxygenates, but suffer from poor product selectivity due to the moderate binding energies of several of the reaction intermediates. Here, we report an ion exchange strategy to construct Cu-Pd paddle wheel dimers within Cu-based metal-organic frameworks (MOFs), [Cu3-xPdx(BTC)2] (BTC=benzentricarboxylate), without altering the overall MOF structural properties. Compared to the pristine Cu MOF ([Cu3(BTC)2], HKUST-1), the Cu-Pd MOF shifts CO2 electroreduction products from diverse chemical species to selective CO generation. In situ X-ray absorption fine structure analysis of the catalyst oxidation state and local geometry, combined with theoretical calculations, reveal that the incorporation of Pd within the Cu-Pd paddle wheel node structure of the MOF promotes adsorption of the key intermediate COOH* at the Cu site. This permits CO-selective catalytic mechanisms and thus advances our understanding of the interplay between structure and activity toward electrochemical CO2 reduction using molecular catalysts.

Trimetallic FeNiCo layered double hydroxide catalysts for industrial-level electrochemical glycerol upgrading

Electrocatalytic conversion of glycerol, a byproduct of biodiesel production, into high value-added chemicals presents a transformative approach for biomass valorization. However, developing stable catalysts that consistently achieve industrial-grade current density at low potentials remains challenging. Herein, a highly efficient FeNiCo-Co(OH)2 electrocatalyst for the glycerol oxidation, by leveraging interconnected FeNiCo layered double hydroxide (LDH) nanosheets grown on a Co(OH)2 precursor is developed. This catalyst achieves an impressive current density of 1000 mA cm−2 at a low voltage of 1.38 V, exhibiting remarkable selectivity for formate and glycollate production. This superior performance stems from the optimized electronic structure and synergistic interactions within the FeNiCo LDHs, enabling the formation of high-valent species at lower potentials, efficient handling reaction intermediates, reduced charge transfer resistance, upward d band center and optimized mass transport, thereby enhancing glycerol adsorption and oxidation. Notably, the electrode exhibits stable operation at 120 mA cm−2 for 32 h and yields 227.50 and 104.17 mmol cm−2 for formate and glycollate, respectively, at industrial current densities for 8 h. This study unveils a novel transition metal-based glycerol oxidation reaction electrocatalyst and lays a foundation for its industrial application, highlighting significant advancements in biomass valorization.

Observation of Ferroelectricity in Carbapenem Intermediates Enables Reactive Oxygen Species Generation by Ultrasound.

Organic ferroelectrics show great applications in the fields of biomedicine, including disease treatment, biosensors, and tissue engineering. Organosilicon pharmaceutical intermediates generally include chiral centers and have satisfying biosafety, biocompatibility, or even biodegradability, which provide versatile platforms for the design of ferroelectricity. However, their academic values in ferroelectricity have long been long overlooked. Here, we demonstrated the ferroelectric properties of 4-acetoxy-azacyclic butanone (4-AA), a key synthetic organosilicon-based intermediate of carbapenem drugs. This compound undergoes a 222F2-type ferroelectric-ferroelastic phase transition at 326 K. As an organic piezoelectric material, 4-AA can produce reactive oxygen species when subjected to ultrasonic vibrations. Combined with its desirable biocompatibility, this material may contribute to antimicrobial and wound healing, tumor treatment, etc. This work will provide inspiration for the discovery of multifunctional biomedical ferroelectric materials as well as their related application prospects.

Stabilisation of Bromenium Ions in Macrocyclic Halogen Bond Complexes.

Halenium ions (X+) are highly reactive electron deficient species that are prevalent transient intermediates in halogenation reactions. The stabilisation of these species is especially challenging, with the most common approach to sequester reactivity through the formation of bis-pyridine (Py) complexes; [(Py)2X]+. Herein, we present the first example of a macrocyclic stabilisation effect for halenium species. Exploiting a series of bis-pyridine macrocycles, we demonstrate that preorganised macrocyclic ligands stabilise bromenium cations via endotopic complexation, impressively facilitating the isolation of a bench stable 'Br+ NO3 -' species. Solid state X-ray crystallographic structural comparison of macrocyclic Br(I) complexes with Ag(I) and Au(I) analogues provides insightful information concerning similarities and stark contrasts in halenium/metal cation coordination behaviors. Furthermore, the first chemical ligand exchange reactions of Br(I) complexes are reported between acyclic [(Py)2Br]+ species and a bis-pyridine macrocyclic donor ligand which importantly highlights a macrocycle effect for halenium cation stabilisation in the solution phase.

Stabilisation of Bromenium Ions in Macrocyclic Halogen Bond Complexes

AbstractHalenium ions (X+) are highly reactive electron deficient species that are prevalent transient intermediates in halogenation reactions. The stabilisation of these species is especially challenging, with the most common approach to sequester reactivity through the formation of bis‐pyridine (Py) complexes; [(Py)2X]+. Herein, we present the first example of a macrocyclic stabilisation effect for halenium species. Exploiting a series of bis‐pyridine macrocycles, we demonstrate that preorganised macrocyclic ligands stabilise bromenium cations via endotopic complexation, impressively facilitating the isolation of a bench stable ‘Br+ NO3−’ species. Solid state X‐ray crystallographic structural comparison of macrocyclic Br(I) complexes with Ag(I) and Au(I) analogues provides insightful information concerning similarities and stark contrasts in halenium/metal cation coordination behaviors. Furthermore, the first chemical ligand exchange reactions of Br(I) complexes are reported between acyclic [(Py)2Br]+ species and a bis‐pyridine macrocyclic donor ligand which importantly highlights a macrocycle effect for halenium cation stabilisation in the solution phase.

A novel approach for the preparation of furandiamines utilizing biomass platform chemicals as substrates via Gabriel synthesis

Primary diamines are significant chemical intermediates and raw materials for high-added-value chemical products, which are regarded as essential monomers in the synthesis of polyamides and polyurethanes. Primary diamines are also particularly pronounced in the automotive, aerospace, and pharmaceutical fields. Among them, 2,5-bis(aminomethyl)furan (BAF) has garnered grant attention as a highly promising renewable diamine. In this work, a new route for the reduction preparation of BAF using a platform compound 5-chloromethylfurfural (CMF) utilizing the Gabriel method was developed, which reasonably avoids the disadvantage of molecular internal polymerization that often occurs in traditional routes that converting BAF from 5-hydroxymethylfurfural (HMF) and HMF derivatives. Additionally, under mild reaction conditions, this novel route yields BAF efficiently by employing Ni/SiO2 as the catalyst. According to the kinetic analysis the reduction process was proved to be predominant. In addition, the analysis of the mechanism showed that compared to other catalysts, Ni/SiO2 contains more active sites and more hydrogen active components (Ni0), achieving an impressive yield of 82.35 % under mild conditions. This work provides a pioneering method for the preparation of BAF, which is crucial for the development of primary diamine preparation.