348 Search Results

Epoxides are important intermediates in synthetic chemistry. Stoichiometric peroxyacids, such as meta-chloroperoxybenzoic acid (mCPBA), are widely used to convert alkenes to epoxides but show poor compatibility with aromatic heterocycles and present hazards when scaled. Herein, we report a highly practical alkene epoxidation method that uses the commercially available iron porphyrin, Fe(TPFPP)Cl (TPFPP = tetrakis(pentafluorophenyl)porphyrin), as a catalyst (0.05 mol %) and aqueous NaOCl as the oxidant in acetonitrile as the solvent. No additional ligands or additives are needed, and the reactions proceed under ambient conditions. The method shows a broad scope, affording high yields of epoxides in reactions with terminalmore » and internal aromatic and aliphatic alkenes, heterocycle-containing substrates, glycals, and polyenes. The practicality of the method is demonstrated in the 100 g scale epoxidation of tri-O-acetyl-D-glucal, which proceeds to completion in 15 min at room temperature.« less

Amine-functionalized solid sorbents are a class of sorbent materials proposed for direct air capture (DAC) of CO₂, yet their long-term performance is susceptible to degradation under realistic operating conditions. Many amines are not thermodynamically stable in air, and amine sorbents oxidize while in use during DAC temperature swing adsorption processes. In this study, we investigate the role of transition metal ion contaminants, specifically Cu²⁺, Fe²⁺, and Ni²⁺, on the oxidative degradation of poly(ethylenimine) (PEI)-impregnated SBA-15 sorbents. By introducing metal ions via different modes mimicking both synthesis-related impurities and impurities derived from environmental exposure, we systematically evaluate sorbent stability after exposuremore » to dry air at an elevated temperature. Thermogravimetric CO₂ uptake measurements reveal that even trace levels of Cu and Fe (as low as ∼4 ppm) can lead to measurable sorbent deactivation after oxidative aging, despite negligible loss in the performance of the control samples. In situ infrared, UV–vis, and X-ray photoelectron spectroscopies indicate that these metals catalyze radical-driven oxidation pathways, altering the chemical structure of the sorbent and accelerating degradation. Our findings underscore the need to account for trace metal contamination during DAC sorbent synthesis and deployment and highlight the importance of environmental contamination pathways.« less

Measurements of sulfuric acid (H₂SO₄) and sulfur trioxide (SO₃) were conducted in Pittsburgh, Pennsylvania, during field campaigns in Fall 2023 and Fall 2024. These measurements identified nocturnal concentrations of H₂SO₄ comparable to those of daytime values. Nocturnal H₂SO₄ concentrations were observed to increase by 5 × 10⁵ to 5 × 10⁷ molecules cm^–3 above background on 16 of the 31 measurement nights. The median peak concentration during events was 6.5 × 10⁶ molecules cm^–3, with a maximum of 1.0 × 10⁸ molecules cm^–3, exceeding previously reported nighttime concentrations. Increases in H₂SO₄ concentrations were positively correlated with the anomalously high SO₃more » concentrations and condensation sink rates, indicating that the formation of H₂SO₄ increased to overcome the loss rates to particles. Increases in particulate mass and the mass fraction of metals commonly emitted from coal combustion and steel production were also observed. The air masses were traced back to the southeast of Pittsburgh, a region home to a steel mill, coke plant, and a steel processing plant. The observations indicate a previously unrecognized nighttime formation pathway for H₂SO₄, potentially from heterogeneous catalysis with metal or black carbon, originating from steel and coke plant emissions. Further measurements are needed to identify key compounds and chemical processes driving these increases in nocturnal H₂SO₄ concentrations.« less

Electrification of 2-butanone synthesis via ketonization of 1-butene offers a viable pathway to reduce emissions associated with its production as a commodity chemical and enhance its prospects as a clean carbon-based synthetic fuel. However, the direct electrochemical ketonization of alkenes remains underexplored, with previous studies largely limited to epoxides and glycols. Herein, we report an electrochemical heterogeneous system optimized for 1-butene ketonization, converting 1-butene to 2- butanone using a bimetallic PdCu catalyst in aqueous electrolytes. The system achieves a Faradaic efficiency of 20% and a partial current density of 0.6 mA/cm² at 1.8 V_RHE. In comparison to monometallic Pd andmore » oxidized PdCu analogs, the PdCu catalyst doubles the ketonization Faradaic efficiency and quadruples the production rate. Postelectrolysis characterization reveals that PdCu preserves the surface metallic alloy phase under anodic polarization, which likely accounts for the enhanced ketonization activity. This work demonstrates the significance of the Pd−Cu speciation dynamics and provides a framework for designing selective electrocatalysts for alkene ketonization.« less

The success of direct air capture (DAC) of CO₂ depends on sorbents that combine high capacity, low energy requirements, and long-term durability. Amine-based sorbents-including solid-supported aminopolymers, grafted amines, and amine-functionalized resins-remain the leading candidates, but their limited lifetimes drive up costs and constrain deployment. In this review, we outline the current understanding of amine-based sorbent degradation with an emphasis on clearly identifying what is known about structure-property-performance relationships, as well as important knowledge gaps. More specifically, we discuss how polymer chemistry, sorbent design variables, and environmental and process conditions contribute to performance loss. In parallel, we outline how advances inmore » spectroscopy, modeling, and accelerated testing are beginning to illuminate chemical and physical degradation mechanisms. Looking forward, we identify future research directions that will be critical for gaining a deeper understanding of degradation, as well as opportunities for developing innovative mitigation strategies for improving the lifetime of amine-based sorbents.« less

Reduction of (depe)₂CrCl₂ (depe = 1,2-bis- (diethylphosphino)ethane) and (dep-benz)₂CrCl₂ (dep-benz = 1,2-bis(diethylphosphino)benzene) under 1 atm of N₂ furnished the dinitrogen complexes (depe)₂Cr(N₂)₂ and (dep-benz)₂Cr(N₂)₂, respectively. One-electron oxidation of these products with FcBAr^F ₄ (Fc = ferrocenium, BAr^F ₄ = B(3,5-(CF₃)₂C₆H₃)₄) yielded the unusual, high-spin tetrahedral complexes [(depe)₂Cr][BAr^F ₄] and [(dep-benz)₂Cr][BAr^F ₄] with concomitant loss of dinitrogen. Reaction of the chromium(I) derivatives with Ph₃CN₃ furnished rare examples of chromium(IV) nitrides as confirmed spectroscopically and by X-ray crystallography. While [(depe)₂Cr(≡N)][BAr^F ₄] underwent association of isocyanides accompanied by partial ligand dissociation, neither chromium nitride was reactive toward H₂ or diphenylsilane under thermal ormore » photochemical conditions. These results distinguish the unique properties of the chromium(IV) nitrides as compared to heavier group 6 congeners and demonstrate both the feasibility of nitride synthesis and the limitations of dinitrogen cleavage and subsequent N−H bond formation.« less

The Rh-catalyzed conversion of olefins and arenes to alkenyl arenes using [(η²-C₂H₄)₂Rh(μ-OPiv)]₂ as the catalyst precursor and 12 ortho- and para-substituted benzoquinone derivatives as the in situ oxidant is reported. Included are comparative studies of the quinone derivatives for (1) rate of styrene production from benzene and ethylene, (2) Markovnikov to anti-Markovnikov selectivity for reactions of benzene and propylene, and (3) ortho/meta/para selectivity when using tert-butylbenzene as the arene. Cyclic voltammetry was utilized to measure reduction potentials for each quinone to determine any possible influence of the quinone redox potential on arene alkenylation rate and selectivity. While significant differences inmore » selectivity are observed between ortho-quinone derivatives, such differences are minimal when para-substituted quinones are utilized. These results suggest that ortho-benzoquinone derivatives likely serve as bidentate ligands, which explains the stronger influence on catalyst activity of ortho-benzoquinone identity compared to para-benzoquinones. Although ortho-benzoquinones generally give styrene production rates faster than those of para-benzoquinones, 3,5-di-tert-butyl-ortho-benzoquinone and ortho-chloranil react with ethylene to form bicyclo[2.2.2]oct-5-ene-2,3-dione derivatives as a significant side product.« less

Formaldehyde (HCHO) is a fundamental chemical feedstock with widespread industrial applications. The direct oxidation of methane by oxygen to formaldehyde (CH₄ + 1/2O₂ → H₂ + HCHO) under mild conditions represents an attractive but challenging transformation, as it requires both activation of the inert C–H bonds of CH₄ and suppression of overoxidation to products such as carbon dioxide. In this work, mass spectrometry experiments combined with theoretical calculations reveal that CoMoO⁺ cations can efficiently mediate this transformation at room temperature. The unique electronic structure of CoMoO⁺ facilitates the formation of a crucial CoMoOCH₂⁺ intermediate during the reaction with CH₄ andmore » prevents methanol formation. In the subsequent oxidation reaction, the Mo atom in CoMoO⁺ serves as the active site for O₂ adsorption, and both Mo and Co atoms act as electron donors to activate O₂, leading to the formation of the C–O bond in formaldehyde. This work reports the first gas-phase example of achieving conversion of CH₄ to HCHO and its radical derivatives by O₂ at room temperature using heteronuclear non-noble metal cations. Remarkably, the CoMoOCH₂⁺ cation maintains high reactivity after adsorbing one or two CH₄ molecules. Finally, these findings provide new mechanistic insights into selective methane activation and conversion.« less

Here, we investigated the mechanisms underlying strong metal-support interactions in CO oxidation using model systems where noble metal crystals support reducible, monolayer-thick CoO_x films. The effect of the Co oxidation state, film thickness, and substrate identity were studied in varying reaction conditions using ambient pressure X-ray photoelectron spectroscopy. At low O₂ pressures, the same oxide phase forms on both Pt(111) and Au(111) surfaces. But when heated at higher O₂ pressures, the oxide phase depends on the substrate. We found that CoO_x/Pt is more active for the CO oxidation reaction than CoO_x/Au, even when both surfaces stabilize the same oxide phase.more » DFT calculations on these and related noble-metal-supported CoO_x films reveal an SMSI-induced reactivity enhancement that strongly depends on the oxide film thickness and which is mediated by charge transfer between the metal and oxide. Charge transfer is also found to correlate with the reaction energy and activation barrier for CO oxidation. This effect was found to be greatest for oxide films on Pt, decreasing on other noble metal supports in the order Pt > Pd > Au > Ag, in agreement with the experiments. The role of charge transfer in the activation barriers and reaction energies provides insight into the nature of SMSI-induced catalytic activity, and suggests that the noble metal work function can serve as an indicator for the strength of SMSI effects.« less

In this work, the conversion of ultrathin 2D-Ni (OH)₂ to NiO is studied using in situ X-ray absorption near edge spectroscopy at the Ni L₃ and O K edges and using variable photon energy X-ray photoelectron spectroscopy at the Ni 2p_3/2 and O 1s edges. The Ni L₃ X-ray absorption spectroscopy and corresponding 2p_3/2 X-ray photoelectron spectroscopy show the oxidation state of the Ni atom to be Ni²⁺ in the course of the reaction; however, the film surface and oxygen defect structure show the presence of a large metallic Ni component before the complete disappearance of the hydroxide phase indicatingmore » oxygen vacancy formation before the completion of water desorption. O 1s spectral changes during heat treatment under ultrahigh vacuum, O₂ dosing, and H₂O dosing suggest the spectral features are due to water desorption and adsorption. Furthermore, by comparing the relative probe depths of X-ray photoelectron spectroscopy and X-ray absorption spectroscopy, it is determined that the surface, at each step in the dehydration process, consists of a combination of Ni, NiO, and Ni (OH)₂ phases, which each contain a mixture of adsorbed hydroxyl groups. Repeated dosing with H₂O, studied with O 1s X-ray photoelectron spectroscopy, suggests that the dissociation of water facilitates the formation of oxygen vacancies.« less