Selective Oxidation Of Cyclohexane Research Articles

Z-Scheme g-C3N4-Au-MoO3-x heterojunction for boosted photocatalytic H2O2 production and enhanced selective oxidation of cyclohexane

Rational design of Z-Scheme photocatalyst with outstanding charge separation and robust redox capabilities for photocatalytic H2O2 generation and cyclohexane oxidation under mild conditions still poses a significant hurdle. In response to this challenge, ternary g-C3N4-Au-MoO3-x composite catalyst was developed though combining in-situ reduced MoO3-x-Au composite and exfoliated g-C3N4 nanosheets using an ultrasonic liquid-phase approach. In addition, variations in the synthesis procedures led to the preparation of g-C3N4−MoO3-x, g-C3N4-Au, and Au-g-C3N4−MoO3-x composites, aimed at exploring their effectiveness in both H2O2 production and catalyzing cyclohexane oxidation. Notably, the g-C3N4-Au-MoO3-x composite exhibited an impressive optical rate of H2O2 generation at 723.18 µmol·L−1·h−1, achieving a 11.94-fold enhancement compared to Au-g-C3N4−MoO3-x. Meanwhile, the conversion rate of cyclohexane reached 11.59 %, with a high selectivity of 97.43 % towards KA oil (cyclohexanol and cyclohexanone), and a KA oil production rate of 1166.86 µmol·L−1·g−1. Through analyzing the photoelectrochemical properties and band energy structures, it has been established that the involvement of an Au mediator was essential and vital for the Z-Scheme electron transfer in g-C3N4-Au-MoO3-x. The incorporation of a Z-scheme heterojunction has resulted in increased light absorption, reduced charge recombination rates, and a substantial elevation in the levels of ·O2− and ·OH radicals, leading to a significant enhancement in photocatalytic efficiency for both H2O2 generation and cyclohexane oxidation. This study opens the door to on-site immediate production of hydrogen peroxide to boost the oxidation efficiency in the photocatalytic cyclohexane oxidation process.

Cover Feature: Ionic liquid templated synthesis of cobalt‐substituted mesoporous aluminophosphates: A novel heterogeneous catalyst for selective oxidation of cyclohexane to cyclohexanol (ChemCatChem 8/2024)

Cover Feature: Ionic liquid templated synthesis of cobalt‐substituted mesoporous aluminophosphates: A novel heterogeneous catalyst for selective oxidation of cyclohexane to cyclohexanol (ChemCatChem 8/2024)

Highly enhanced direct catalytic oxidation of cyclohexane to adipic acid by prussian blue analogues-derived C, N doped CuCo composite catalysts

The oxidation of cyclohexane to produce adipic acid suffered from the inefficient and polluting two-step process. We introduce the CuCo Prussian blue analogues derived in situ C, N doped CuCo composite catalysts in the selective oxidation of cyclohexane. Due to the in-situ doping of C and N elements in the form of active graphite carbon and pyridine nitrogen, the oxygen vacancy content and the ability to activate oxygen are improved. The one-step efficient catalytic oxidation of cyclohexane to adipic acid was realized due to the excellent electron transfer performance between C, N elements and metals.

Roles of the A-Site Ca Dopant in Modifying Surface Properties of a Co-Based Perovskite Catalyst for Selective Oxidation of Cyclohexane

Roles of the A-Site Ca Dopant in Modifying Surface Properties of a Co-Based Perovskite Catalyst for Selective Oxidation of Cyclohexane

Ionic liquid templated synthesis of cobalt‐substituted mesoporous aluminophosphates: A novel heterogeneous catalyst for selective oxidation of cyclohexane to cyclohexanol

AbstractOrdered hexagonal mesoporous aluminophosphate and its cobalt‐substituted analogue were successfully synthesized using ionic liquid as a structure‐directing agent. The resulting materials were systematically characterized by various analytical, spectroscopic, and imaging methods, confirming the presence of divalent cobalt in the tetrahedral framework of the matrix. Further, the high surface area, pore volume, and thicker mesopore walls of these materials impart good thermal and hydrothermal stability. The mesoporous catalysts showed excellent activity towards the oxidation of cyclohexane reactions using hydrogen peroxide as an oxidant, with 98.5 % conversion and 90.4 % selectivity towards cyclohexanol.

Prussian Blue Analogue-Derived Co3O4 as Catalysts for Enhanced Selective Oxidation of Cyclohexane Using Molecular Oxygen.

Selective conversion of inert C-H bonds in alkanes into high-value-added functional groups (alcohols, ketones, carboxylic acids, etc.) plays a vital role in establishing a green and sustainable chemical industry. Catalytic selective oxidation of cyclohexane to KA oil (cyclohexanol and cyclohexanone) is a typical representative of alkane functionalization. In this work, hollow cage-like Co3O4 (Co3O4-C) and particle Co3O4 (Co3O4-P) were synthesized by calcining two types of Prussian blue analogues (PBAs), which were used to catalyze the selective oxidation of cyclohexane. The Co3O4-C predominantly exposed (311) crystal plane is easier to adsorb cyclohexane than Co3O4-P, which is beneficial to shorten the induction period, accelerate the reaction rate, and improve the conversion. Consequently, Co3O4-C displayed a 10% conversion of cyclohexane within 1 h, and the KA oil selectivity reached 90%. The Co3O4-P exposed (220) crystal plane has a higher molar percentage of oxygen vacancies and more active oxygen species, as well as a strong cyclohexanone adsorption capacity, which is conducive to the deep oxidation of cyclohexanone to adipic acid and other diacid products. The mechanism analysis of cyclohexane oxidation catalyzed by PBA-based Co3O4 shows that it exemplifies the feasibility to tailor the surface of catalysts by modulating the PBAs, which ultimately influences their reaction performance for accelerating the reaction and maintaining high cyclohexane conversion and KA oil selectivity.

Selective oxidation of cyclohexane over nanostructured manganese tungstate: Contribution of Mn and W related sites

Nanostructured MnWO4 catalysts prepared with different initial pH exhibited systematic variation in the activity in the selective oxidation of cyclohexane. 2-propanol TPD showed that the ratio of Mn to W related sites increased with the initial synthesis pH. W sites were found to be mainly active in the formation of CHHP and dehydrogenation of cyclohexanol, while Mn sites appeared to be more active in decomposition of CHHP and deep oxidation, giving a significant selectivity to adipic acid. The high yield of KA oil at intermediate synthesis pH suggests an optimum balance of Mn and W surface sites.

The Deposition of Isolated Fe(3+) Species in Mesoporous Silicon for Oxidation of Cyclohexane

AbstractThe balance of activity and selectivity in liquid alkane oxidation is challenging for the design of supported Fe catalysts. When Fe species leach to the solvent, uncontrolled free radical chain reactions happen. Herein, isolated Fe(3+) species were constructed by forming a strong Fe−O−Si bond for the selective oxidation of cyclohexane to cyclohexanone by H2O2. Compared to the supported FeOx clusters, the strong Fe−O−Si bond between isolated Fe(3+) species and SiO2 prevents the leaching of Fe in strong oxidation (H2O2) reaction conditions and dominates the non‐free radical mechanism. The turnover frequency over 10FeOx/SBA‐15 reached 15.2 h−1, higher than for reported Fe‐based catalysts. High selectivity of cyclohexanone is maintained at different conversions. Moreover, the (SiO)xFe3+(OH)3‐x−OOH active species were detected by Raman and FTIR and are generated from the oxidation of isolated Fe species. The strong Fe−O−Si bond and non‐free‐radical mechanism by (SiO)xFe3+(OH)3‐x−OOH active species induce high activity and selectivity for the oxidation of many other alkanes.

One-step highly selective catalytic oxidation of cyclohexane to KA-oil over functional CeMn0.5Co0.5Ox composite oxide: Synergistic effects between Mn and Co species with different valences and metal ion ratios

Presently, one-step highly selective oxidation of cyclohexane to KA-oil, which is a crucial organic chemical intermediate for the production of ε-caprolactam and adipic acid, is still a tremendous challenge. In this work, the functional CeMn0.5Co0.5Ox composite oxide catalysts were successfully prepared by glycine-nitrate combustion method. The results showed that 93.0% of selectivity to KA-oil with 4.6% of cyclohexane conversion was achieved over CeMn0.5Co0.5Ox under the optimal reaction conditions. The experimental and characterization results showed that the excellent catalytic performance of CeMn0.5Co0.5Ox is attributed to the synergistic effects between Mn and Co species with different valences and metal ion ratios, which efficiently promote the directional decomposition or reduction of cyclohexyl hydroperoxide (CHHP) intermediate to KA-oil. The density functional theory (DFT) calculations further confirmed the synergistic catalysis of CeMn0.5Co0.5Ox in the selective oxidation. This work affords the new insights into the design of efficient catalyst for the selective oxidation of alkanes.

Chemo‐Enzymatic One‐Pot Oxidation of Cyclohexane via in‐situ H2O2 Production over Supported AuPdPt Catalysts

AbstractThe introduction of dopant concentrations of Pt into supported AuPd nanoparticles, when used in conjunction with an evolved unspecific peroxygenase (UPO) from Agrocybe aegerita (PaDa‐I) is demonstrated to offer high efficacy towards the one‐pot selective oxidation of cyclohexane to KA oil (cyclohexanol and cyclohexanone), via the in‐situ synthesis of H2O2. The optimised AuPdPt/TiO2/PaDa‐I system achieves significant improvements over analogous AuPd or Pd‐only formulations or the use of commercially available H2O2, with this attributed to the increased rate of H2O2 production by the chemo‐catalyst, which results from the electronic modification of Pd species via Pt incorporation, upon the formation of trimetallic nanoalloys.

Selective cyclohexane oxidation enhancement by electronic structures regulation of metal-poly(ionic liquid)s

Poly(ionic liquids) (PILs) combined with the macromolecular structure and unique properties of ionic liquids show unlimited potential in catalysis. In this work, a series of metal-based PIL with different ionic ratios were prepared for the selective oxidation of cyclohexane. Characterization analysis reveals that different degrees of ionization could adjust the Co–N sites of the catalysts efficiently, leading to significant changes in their electronic structure, which strongly relate to catalytic performance in oxidation. 20.07% cyclohexane conversion and 13.06% cyclohexanone and cyclohexanol (KA oil) yield can be achieved by metal-based PILs that are better than other commercial catalysts. Compared with CoCl2, metal-based PILs perform well, with superior conversion and KA oil yield. More interestingly, the catalyst created in this study features a malleable Co–N site, which may potentially have an impact on how oxygen species adsorb and desorb from the catalyst. Therefore, the catalyst studied in this work is used as molecular oxygen for the selective oxidation of cyclohexane to produce KA oil, and its application prospect is promising.

Selective Oxidation of Cyclohexane to Cyclohexanol/Cyclohexanone by Surface Peroxo Species on Cu-Mesoporous TiO2.

Selective oxidation of cyclohexane to cyclohexanol/cyclohexanone (KA-oil) is an important chemical process, which is still constrained by low conversion and selectivity and high energy consumption. In this study, Cu-doped mesoporous TiO2 (Cu-MT) has been successfully synthesized via calcinating MIL-125(Ti) doped with copper acetylacetonate, which shows high reactivity in selective oxidation of cyclohexane to KA-oil by persulfate (PS) with the desirable cyclohexane conversion of 16.8% and a selectivity of 98.0% under mild conditions and the low ratio of PS/cyclohexane of 1:1. A series of characterizations and density functional theory calculations reveal that the doped Cu(I,II) on Cu-MT is the reactive site for non-radical activation of PS with the moderate elongation of the O-O bond in PS, which then abstracts 1H (1H+ + 1e-) from cyclohexane to form Cy• and eventually KA-oil. This study gives new insight on the importance of moderately activated PS in selective oxidation of C-H.

Liquid phase selective oxidation of cyclohexane using gamma alumina doped manganese catalysts and ozone: an insight into reaction mechanism

Abstract In this study, we investigate the oxidation of cyclohexane using various percentages of Mn/γ-Al2O3 catalysts. The catalysts were characterized with various spectroscopic and microscopic techniques. The XRD showed the presence of γ-Al2O3 and MnO only. However, the XPS showed that AlO, AlOH, Mn2O3 and MnO2 also exist. The TEM results of pristine γ-Al2O3 showed characteristics of a spherically shaped material, whereas Mn/γ-Al2O3 catalysts displayed rod shaped particles. The EPR results showed that hydroxide radicals are the main reactive species responsible for the significant oxidation of cyclohexane and the catalysts play a profound role in the generation of hydroxide radicals. The oxidation of cyclohexane was performed for 1 h and the reaction products were analysed using GC-MS and FT-IR in 30 min intervals. The 2.5% Mn/γ-Al2O3 was the most reactive catalyst with a percentage conversion of 33% after 1 h oxidation. The cyclohexanol and the cyclohexanone were the only reaction products obtained. This study exhibited that Mn/γ-Al2O3 catalysts when used in conjunction with ozone are potential replacement for industrially used homogeneous manganese catalysts.

Bio-inspired V-TiO2 architectures with regulable surface ultrastructure for visible-light photocatalytic selective oxidation of cyclohexane

Photocatalytic selective oxidation of cyclohexane is more energy saving and sustainable when compared with traditional thermal catalysis, but highly effective visible-light photocatalyst for this reaction remains challenging. Herein, vanadium-doped TiO2 was prepared by using a solvent-thermal-assisted biotemplating method, while glycerol was used to regulate the surface ultrastructure of the catalyst. It is found that the use of the biotemplate, regulation of the surface ultrastructure of the catalyst by glycerol, as well as vanadium doping are all beneficial to improve the performance of the photocatalyst. Resultantly, the biotemplated TiO2 doped with 2 % vanadium, which has a needle-like surface ultrastructure (2 %V-CTiO2(g)) achieves the best performance for cyclohexane conversion (0.98 %), which is 7.0, 8.9 and 49 times higher than TiO2 sample without vanadium doping, surface ultrastructure adjustment and biotemplating, respectively. Characterizations and DFT calculations confirm that biotemplating and the use of glycerol endow the sample with unique morphology, oxygen vacancies and high surface area. Doping of vanadium not only changes the band structure of TiO2 but also introduces the interconversion of V4+ and V5+ into the photocatalytic process. This work offers a new approach to the green conversion of cyclohexane.

Engineering of mixed metal oxides photocatalysts derived from transition-metal-based layered double hydroxide towards selective oxidation of cyclohexane under visible light

In this work, visible-light-driven mixed metal oxide nanostructures were synthesized selecting layered double hydroxide (LDHs) as precursors. Such LDHs-derived mixed metal oxide photocatalysts possessed distinct difference in cyclohexane oxidation under visible light, which was mainly due to the controllable composition of metal cations. Through the analysis of photocatalytic performances, it was figured out that, Cr0.2Mg3AlO showed the best catalytic activity among the series of photocatalysts, possessing 12.5% conversion and 96.7% recyclability for oxidation of cyclohexane. The superior oxidation performance of Cr0.2Mg3AlO was largely dependent on the formation of MgAlO/MgCr2O4 heterojunction, and it matched band structure could effectively enhance the absorption of visible light and the separation of electron-holes, and therefore accelerated the photocatalytic activity. This work provided an effective strategy for the preparation of highly efficient photocatalysts toward oxidation of cyclohexane.

Solvent-free selective oxidation of cyclohexane to KA oil in air over CoWO4@W18O49 catalyst

The challenge for researchers in heterogeneous catalysis is to develop robust catalysts while using benign reaction conditions, without producing unwanted by-products and preventing leaching of metal during the processes. We have synthesized nanosized CoWO4@W18O49 catalyst with oxygen vacancy sites for molecular oxygen activation from air, and this catalyst selectively oxidized cyclohexane to KA oil (KA oil referred to ketone-alcohol oil) in solvent-free conditions, where under optimum conditions, ∼24 % cyclohexane conversion with ∼93 % KA oil selectivity was achieved. The catalyst has been synthesized by the co-precipitation method and studied with the help of various analytical tools. DFT studies were also performed to calculate the energy needed for the oxygen vacancy generation over the CoWO4 (111), W18O49 (010) and CoWO4@W18O49 (010) surfaces. The energy required for the removal of oxygen atom at the CoWO4@W18O49 (010) surface was found to be − 15.8 kJ/mol, which is 96.2 kJ/mol and 46.9 kJ/mol lower than the CoWO4 (111) and W18O49 (010) surfaces respectively. The exceptional catalytic activity of CoWO4@W18O49 is an outcome of the combined contribution of the active CoWO4 and W18O49 interfaces, which have redox sites and a lot of vacancies of oxygen that benefit from the effective interaction.

High performance BaCO3-CeO2 composite catalyst for solvent-free selective oxidation of cyclohexane with molecular oxygen

BaCO3-CeO2 composite catalysts were prepared by the hydrothermal synthesis method, and the influence of Ba/Ce on the structural and catalytic performance for selective oxidation of cyclohexane with molecule oxygen was studied. The characterization results exhibited that the doping amount of BaCO3 would influence the morphology, the content of surface Ce3+ and surface oxygen species (Oβ), and alkalinity. Meanwhile, the amount of alkali is the key to the decomposition of cyclohexyl hydrogen peroxide (CHHP). 10.5% conversion of cyclohexane and 85.0% selectivity of KA oil were achieved under the reaction conditions of 1.0 MPa O2 and 150 °C for 2 h. The excellent catalytic activity was attributed to its high atomic ratios of Ce3+/Cetotal and Oβ/Ototal on the surface and optimal redox capacity.

Concepts of Heterogeneously Catalyzed Liquid‐Phase Oxidation of Cyclohexene with tert‐Butyl Hydroperoxide, Hydrogen Peroxide and Molecular Oxygen

AbstractThe oxidation of hydrocarbons is of great significance for the chemical industry as it provides access to valuable functionalized chemicals. The oxidation of cyclohexene has raised much interest because it enables the direct synthesis of adipic acid, which is an important building block in polymer chemistry. However, the selective oxidation of cyclohexene is rather challenging due to its two reactive centers so that epoxidation or allylic oxidation may occur leading to a variety of products. Whether the oxidation takes place at the allylic C−H bond or at the C=C bond is strongly influenced by the chosen oxidant and catalyst, and different reaction mechanisms can occur. Therefore, this concept article aims at giving a broad overview of the recent advances in the selective cyclohexene oxidation over heterogeneous transition metal‐based catalysts using environmentally benign oxidants like tert‐butyl hydroperoxide, H2O2 and molecular O2.

Design of Prussian Blue Analogue-Derived Magnetic Binary Ce–Fe Oxide Catalysts for the Selective Oxidation of Cyclohexane

Design of Prussian Blue Analogue-Derived Magnetic Binary Ce–Fe Oxide Catalysts for the Selective Oxidation of Cyclohexane

Synthesis of a highly active Nb2O5 for 1,2-cyclohexanediol production

A commercial niobium oxide was used to form a gelled material, which was lyophilized producing a novel polyoxoniobate catalyst (L-AmNbO) containing peroxo groups. The activity of this new catalyst was assessed through oxidation reactions of the cyclohexene. In the presence of L-AmNbO catalyst, the oxidation of cyclohexene with H2O2 reached 90% of conversion after 12 h at 75 °C, with selectivity for 1,2-cyclohexanediol (∼ 50%). The catalytic results and the surface properties of this new material indicated that it can be a promising catalyst for niobium compounds applications in the selective oxidation of cyclohexene.