2-Methylimidazole Copper Iminodiacetates for the Adsorption of Oxygen and Catalytic Oxidation of Cyclohexane.
Ontology highlight
ABSTRACT:
SUBMITTER: Chen X
PROVIDER: S-EPMC7143979 | biostudies-literature |
REPOSITORIES: biostudies-literature
Similar Datasets
Project description:The direct catalytic conversion of methane to liquid oxygenated compounds, such as methanol or dimethyl ether, at low temperature using molecular oxygen is a grand challenge in C-H activation that has never been met with synthetic, heterogeneous catalysts. We report the first demonstration of direct, catalytic oxidation of methane into methanol with molecular oxygen over copper-exchanged zeolites at low reaction temperatures (483-498 K). Reaction kinetics studies show sustained catalytic activity and high selectivity for a variety of commercially available zeolite topologies under mild conditions (e.g., 483 K and atmospheric pressure). Transient and steady state measurements with isotopically labeled molecules confirm catalytic turnover. The catalytic rates and apparent activation energies are affected by the zeolite topology, with caged-based zeolites (e.g., Cu-SSZ-13) showing the highest rates. Although the reaction rates are low, the discovery of catalytic sites in copper-exchanged zeolites will accelerate the development of strategies to directly oxidize methane into methanol under mild conditions.
| S-EPMC4919767 | biostudies-literature
Project description:BACKGROUND:The oxidation of cyclohexane under mild conditions occupies an important position in the chemical industry. A few soluble transition metals were widely used as homogeneous catalysts in the industrial oxidation of cyclohexane. Because heterogeneous catalysts are more manageable than homogeneous catalysts as regards separation and recycling, in our study, we hydrothermally synthesized and used pure berlinite (AlPO4) and vanadium-incorporated berlinite (VAlPO4) as heterogeneous catalysts in the selective oxidation of cyclohexane with molecular oxygen under atmospheric pressure. The catalysts were characterized by means of by XRD, FT-IR, XPS and SEM. Various influencing factors, such as the kind of solvents, reaction temperature, and reaction time were investigated systematically. RESULTS:The XRD characterization identified a berlinite structure associated with both the AlPO4 and VAlPO4 catalysts. The FT-IR result confirmed the incorporation of vanadium into the berlinite framework for VAlPO4. The XPS measurement revealed that the oxygen ions in the VAlPO4 structure possessed a higher binding energy than those in V2O5, and as a result, the lattice oxygen was existed on the surface of the VAlPO4 catalyst. It was found that VAlPO4 catalyzed the selective oxidation of cyclohexane with molecular oxygen under atmospheric pressure, while no activity was detected on using AlPO4. Under optimum reaction conditions (i.e. a 100 mL cyclohexane, 0.1 MPa O2, 353 K, 4 h, 5 mg VAlPO4 and 20 mL acetic acid solvent), a selectivity of KA oil (both cyclohexanol and cyclohexanone) up to 97.2% (with almost 6.8% conversion of cyclohexane) was obtained. Based on these results, a possible mechanism for the selective oxidation of cyclohexane over VAlPO4 was also proposed. CONCLUSIONS:As a heterogeneous catalyst VAlPO4 berlinite is both high active and strong stable for the selective oxidation of cyclohexane with molecular oxygen. We propose that KA oil is formed via a catalytic cycle, which involves activation of the cyclohexane by a key active intermediate species, formed from the nucleophilic addition of the lattice oxygen ion with the carbon in cyclohexane, as well as an oxygen vacancy formed at the VAlPO4 catalyst surface.
| S-EPMC5884748 | biostudies-literature
Project description:Inorganic particles are effective photocatalysts for the liquid-state production of organic precursors and monomers at ambient conditions. However, poor colloidal stability of inorganic micro- and nanoparticles in low-polarity solvents limits their utilization as heterogeneous catalysts and coating them with surfactants drastically reduces their catalytic activity. Here we show that effective photo-oxidation of liquid cyclohexane (CH) is possible using spiky particles from metal oxides with hierarchical structure combining micro- and nanoscale structural features engineered for enhanced dispersibility in CH. Nanoscale ZnO spikes are assembled radially on α-Fe2O3 microcube cores to produce complex 'hedgehog' particles (HPs). The 'halo' of stiff spikes reduces van der Waals attraction, preventing aggregation of the catalytic particles. Photocatalysis in Pickering emulsions formed by HPs with hydrogen peroxide provides a viable pathway to energy-efficient alkane oxidation in the liquid state. Additionally, HPs enable a direct chemical pathway from alkanes to epoxides at ambient conditions, specifically to cyclohexene oxide, indicating that the structure of HPs has a direct effect on the recombination of ion-radicals during the hydrocarbon oxidation. These findings demonstrate the potential of inorganic photocatalysts with complex architecture for 'green' catalysis.
| S-EPMC9932155 | biostudies-literature
Project description:Controlling the surface is necessary to adjust the essential properties and desired functions of nanomaterials and devices. For nanostructured multivalent vanadium oxides, unwanted surface oxidation occurs at ambient atmosphere generally and needs to be suppressed or avoided. We describe the suppressed surface oxidation of VO2 nanostructures through blocking oxygen adsorption. During an enhanced photoinduced surface oxidation process, the increased oxidation states of vanadium in VO2 nanostructures are suppressed by the use of an inert atmosphere or coating. Intermediate oxidation states are observed, and an ALD-TiO2 coating has a good antioxidant capacity for preventing the formation of oxygen-enriched components. Such oxidation suppression is beneficial to improving the stability of VO2 nanostructures. Controllable surface oxidation helps us to understand the physical essentials of surface chemical reactions and achieve better control of surface functions and performances on correlated vanadium oxide nanostructures.
| S-EPMC6822112 | biostudies-literature
Project description:Copper-containing mixed metal oxides are one of the most promising catalysts of selective catalytic oxidation of ammonia. These materials are characterized by high catalytic efficiency; however, process selectivity to dinitrogen is still an open challenge. The set of Cu-Zn-Al-O and Ce/Cu-Zn-Al-O mixed metal oxides were tested as catalysts of selective catalytic oxidation of ammonia. At the low-temperature range, from 250 °C up to 350 °C, materials show high catalytic activity and relatively high selectivity to dinitrogen. Samples with the highest Cu loading 12 and 15 mol.% of total cation content were found to be the most active materials. Additional sample modification by wet impregnation of cerium (8 wt.%) improves catalytic efficiency, especially N2 selectivity. The comparison of catalytic tests with results of physicochemical characterization allows connecting the catalysts efficiency with the form and distribution of CuO on the samples' surface. The bulk-like well-developed phases were associated with sample activity, while the dispersed CuO phases with dinitrogen selectivity. Material characterization included phase composition analysis (X-ray powder diffraction, UV-Vis diffuse reflectance spectroscopy), determination of textural properties (low-temperature N2 sorption, scanning electron microscopy) and sample reducibility analysis (H2 temperature-programmed reduction).
| S-EPMC8585330 | biostudies-literature
Project description:We study the allylic oxidation of cyclohexene with O2 under mild conditions in the presence of transition-metal catalysts. The catalysts comprise nanometric metal oxide particles supported on porous N-doped carbons (M/N:C, M=V, Cr, Fe, Co, Ni, Cu, Nb, Mo, W). Most of these metal oxides give only moderate conversions, and the majority of the products are over-oxidation products. Co/N:C and Cu/N:C, however, give 70-80?% conversion and 40-50?% selectivity to the ketone product, cyclohexene-2-one. Control experiments in which we used free-radical scavengers show that the oxidation follows the expected free-radical pathway in almost all cases. Surprisingly, the catalytic cycle in the presence of Cu/N:C does not involve free-radical species in solution. Optimisation of this catalyst gives >85?% conversion with >60?% selectivity to the allylic ketone at 70?°C and 10?bar O2. We used SEM, X-ray photoelectron spectroscopy and XRD to show that the active particles have a cupric oxide/cuprous oxide core-shell structure, giving a high turnover frequency of approximately 1500?h-1. We attribute the high performance of this Cu/N:C catalyst to a facile surface reaction between adsorbed cyclohexenyl hydroperoxide molecules and activated oxygen species.
| S-EPMC5873426 | biostudies-literature
Project description:Supported atomic metal sites have discrete molecular orbitals. Precise control over the energies of these sites is key to achieving novel reaction pathways with superior selectivity. Here, we achieve selective oxygen (O2) activation by utilising a framework of cerium (Ce) cations to reduce the energy of 3d orbitals of isolated copper (Cu) sites. Operando X-ray absorption spectroscopy, electron paramagnetic resonance and density-functional theory simulations are used to demonstrate that a [Cu(I)O2]3- site selectively adsorbs molecular O2, forming a rarely reported electrophilic η2-O2 species at 298 K. Assisted by neighbouring Ce(III) cations, η2-O2 is finally reduced to two O2-, that create two Cu-O-Ce oxo-bridges at 453 K. The isolated Cu(I)/(II) sites are ten times more active in CO oxidation than CuO clusters, showing a turnover frequency of 0.028 ± 0.003 s-1 at 373 K and 0.01 bar PCO. The unique electronic structure of [Cu(I)O2]3- site suggests its potential in selective oxidation.
| S-EPMC7419315 | biostudies-literature
Project description:In this work, a consecutive adsorption-catalysis approach to remove Cu2+ ions and catalytic reduction of 4-nitrophenol (4-NP) is proposed. Attapulgite (ATP) nanorods are utilized as adsorbents to enrich Cu2+ ions from contaminated water. Subsequently, the adsorbed ions were in situ reduced to construct Cu-loaded ATP catalysts. The catalytic activities of the composite ATP-Cu catalysts are evaluated by 4-NP reduction in the presence of NaBH4. The optimal ATP-Cu50 sample prepared by putting ATP into a 50 mg L-1 CuSO4 solution could complete the catalytic reaction within 4 min. Moreover, the Cu-deposited ATP nanorods can be integrated into a continuous flow catalytic system, and the 4-NP can be rapidly reduced. This method sheds lights on the fabrication of ATP-based hybrid catalysts and the removal of multiple water pollutants.
| S-EPMC7496003 | biostudies-literature
Project description:Singlet oxygen (1O2) plays a pivotal role in numerous catalytic oxidation processes utilized in water purification and chemical synthesis. The spin-trapping method based on electron paramagnetic resonance (EPR) analysis is commonly employed for 1O2 detection. However, it is often limited to time-independent acquisition. Recent studies have raised questions about the reliability of the 1O2 trapper, 2,2,6,6-tetramethylpiperidine (TEMP), in various systems. In this study, we introduce a comprehensive, kinetic examination to monitor the spin-trapping process in EPR analysis. The EPR intensity of the trapping product was used as a quantitative measurement to evaluate the concentration of 1O2 in aqueous systems. This in situ kinetic study was successfully applied to a classical photocatalytic system with exceptional accuracy. Furthermore, we demonstrated the feasibility of our approach in more intricate 1O2-driven catalytic oxidation processes for water decontamination and elucidated the molecular mechanism of direct TEMP oxidation. This method can avoid the false-positive results associated with the conventional 2D 1O2 detection techniques, and provide insights into the reaction mechanisms in 1O2-dominated catalytic oxidation processes. This work underscores the necessity of kinetic studies for spin-trapping EPR analysis, presenting an avenue for a comprehensive exploration of the mechanisms governing catalytic oxidation processes.
| S-EPMC10372693 | biostudies-literature
Project description:During olive oil extraction, large amounts of phenolics are generated in the corresponding wastewaters (up to 10 g dm-3). This makes olive oil mill wastewater toxic and conventional biological treatment challenging. The catalytic wet peroxide oxidation process can reduce toxicity without significant energy consumption. Hydrogen peroxide oxidation of phenolics present in industrial wastewaters was studied in this work over copper catalysts focusing on understanding the impact of mass transfer and establishing the reaction kinetics. A range of physicochemical methods were used for catalyst characterization. The optimal reaction conditions were identified as 353 K and atmospheric pressure, giving complete conversion of total phenols and over 50% conversion of total organic carbon content. Influence of mass transfer on the observed reaction rate and kinetics was investigated, and parameters of the advanced kinetic model and activation energies for hydrogen peroxide decomposition and polyphenol oxidation were estimated.
| S-EPMC6644426 | biostudies-literature