Conversion Of Cyclohexanol Research Articles

Using novel open-framework copper borovanadate as an effective catalyst in the conversion of cyclohexanol to cyclohexanone

A new open-framework copper borovanadate containing two oxidation states of V4+ and V5+ cations {[Cu5(1,2-dap)10][VV2VIV10B18O54(OH)6(H2O)]}·2H3BO3·9H2O (1,2-dap: 1, 2-propylene diamine) (1) using 1,2-dap as template agent has been successfully prepared. It is composed of five coordination cations [Cu(1,2-dap)2]2+and one borovanadate anion [VV2VIV10B18O54(OH)6(H2O)]10- constructed by one {B18O30(OH)6} and two {V6O18} subunits, as well as two isolated H3BO3 molecules and nine H2O molecules. The compound exhibits for the first time penta-coordinated copper cations, uncoordinated H3BO3 molecules and 1, 2-dap ligands in the series of open-framework borovanadates. Its UV diffuse-reflectance spectrum, Mott-Schottky curve, fluorescent emission, chromaticity and second-order lifetime were investigated in detail. The stable pH range (5.8–2.3) of the borovanadate anion in DMF solution was explored by means of fluorescence and UV spectra. In particular, it showed effective catalytic activity in the conversion of cyclohexanol to cyclohexanone (conversion: 86.8 %, selectivity: 97.4 %). The possible catalytic mechanism for the catalytic reaction had been also established. The studies revealed that the borovanadate could be used as a potential stable catalyst for the selective oxidation of cyclohexanol.

Selective regulation of products for guaiacol hydrodeoxygenation by adjusting type and acidity of supports

Upgrading lignin-oil into advanced fuels or chemicals has been widely studied in recent years. To understand the effect of support type and acidity on the hydrodeoxygenation (HDO) of guaiacol (lignin-oil model compound), Ni-based catalysts were prepared with SiO2, Al2O3 and ZSM-5 as supports, respectively. The catalysts were characterized by X-ray diffraction (XRD), N2 adsorption desorption, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and Pyridine adsorption Fourier-transform infrared (Py-IR). The research results indicate that selective regulation of guaiacol hydrogenation products can be achieved by changing the type and acidity of support. Cyclohexanol is the main product over Ni/SiO2, while cyclohexane is the main product over Ni/ZSM-5 series catalysts. Moreover, as the Si/Al ratio increases, the catalytic activity of Ni/ZSM-5 slightly decreases, and the yield of cyclohexane also decreases. The Brønsted acidity of the support is the key to promoting the conversion of cyclohexanol to cyclohexane. The formation of NiAl2O4 is the main reason for the relatively low activity of Ni/Al2O3. The conversion of guaiacol is as high as 99.2 %, and the yield of cyclohexane is as high as 86.6 % over Ni/ZSM-5(Si/Al = 27). In addition, complete conversion of guaiacol and 92.6 % yield of cyclohexanol were achieved over Ni/SiO2. More importantly, Ni/SiO2 and Ni/ZSM-5(27) are suitable for aromatic substrates with different substituents, respectively.

Selective oxidation of cyclohexanol to cyclohexanone with peroxydisulfate over Co/N doped porous carbon

Cyclohexanone serves as a vital chemical intermediate in nylon production and as a solvent in the manufacturing of resins and paints. The quest for facile, environmentally-friendly, and cost-effective methods to achieve selective oxidation of cyclohexanol is highly desirable. In this study, we successfully achieved the oxidation in water solution using peroxydisulfate (PDS) activation. This was accomplished by employing a Co/N doped porous carbon catalyst synthesized through the one-step carbonization of zeolite-imidazolate frameworks (ZIFs). The catalysts derived from ZIFs with various Co/Zn ratios were extensively characterized using XRD, SEM, TEM, N2 adsorption–desorption, and XPS techniques. The catalyst's performance was assessed under different reaction conditions, including reaction temperature, PDS dosage, and water quality. Notably, the results revealed that under mild conditions, a high efficiency was achieved with over 55% cyclohexanol conversion and 80% cyclohexanone selectivity within 3 h. To gain a greater understanding of the reactive oxygen species involved, we conducted further quenching experiments and EPR analysis. Our findings suggested that·SO4-, ·OH, and mediated electron transfer played a dominant role in the oxidation process. The insights obtained from this work have the potential to offer a green and economically viable method for the selective oxidation of cyclohexanol to cyclohexanone.

Highly-dispersed Ni3Fe alloy nanoparticles anchored on MgAl-LDO for efficient catalytic amination of KA-oil to cyclohexylamine

The partial oxidation of cyclohexylamine to cyclohexanone oxime provides the new approach for preparation of caprolactam, which is vital important monomer of nylon-6 fibers and resins. In this work, a simple and efficient reductive amination of KA-oil to cyclohexylamine was developed over hydrotalcite-derived 9 %Ni-3 %Fe/MgAl-LDO catalyst. The results showed that the 9 %Ni-3 %Fe/MgAl-LDO catalyst exhibited the excellent catalytic performance, 97 % of cyclohexanol conversion and 99 % of cyclohexanone conversion were achieved with 98 % of selectivity to cyclohexylamine over 100 h at 170 °C. The highly-dispersed Ni3Fe alloy nanoparticles anchored on MgAl-LDO are responsible for the excellent catalytic performance and stability of catalyst. Moreover, the Ni sites of Ni3Fe alloy (111) facet as dominant catalytic active sites were identified by DFT calculation. The present work provides a new approach for green preparation of cyclohexylamine from reductive amination of KA-oil over hydrotalcite-derived 9 %Ni-3 %Fe/MgAl-LDO catalyst, and has important industrial application prospects.

High-entropy oxide-derived Cu catalysts for the coupling reaction of cyclohexanol dehydrogenation with acetone hydrogenation

A reduced Cu0.75Zn0.15Mg7.1Al1Sc1O11-HEO catalyst was highly active and stable for the dehydrogenation of cyclohexanol, and the conversion of cyclohexanol could be evidently enhanced when acetone was used as the solvent and/or hydrogen acceptor.

Highly Dispersed and Stable Hydrotalcite-Derived NiCu/MgAlO Alloy Catalyst for Efficient Amination of Cyclohexanol to Cyclohexylamine in the Vapor Phase

Developing a mild and efficient method for highly selective amination of alcohols to amines as important versatile compounds is very interesting in the organic synthesis field. In this work, we have developed a simple and efficient approach for high-yield preparation of cyclohexylamine from the vapor-phase catalytic amination of cyclohexanol with ammonia under atmospheric pressure. The results indicated that the hydrotalcite-derived NiCu/MgAlO alloy catalyst exhibited excellent catalytic performance and stability, and 98% cyclohexanol conversion with 95% selectivity toward cyclohexylamine had still been maintained after running for over 300 h at 170 °C. The super high activity and stability of the NiCu/MgAlO catalyst are attributed to the active Ni–Cu alloy nanoparticles with high dispersion and uniform particle size (about 4 nm). DFT calculation results indicated the Ni site of the NiCu alloy (111) facet as the main catalytic active site. The energy profiles for the potential comparative free energy of cyclohexanol to cyclohexylamine on the NiCu alloy (111) facet were calculated. This approach employing a highly dispersed and stable Ni–Cu bimetallic alloy catalyst for efficient amination of cyclohexanol to cyclohexylamine in the vapor phase is promising and has potential industrial application prospects. Especially, the designed Ni–Cu alloy catalyst can also be applied in the amination of other alcohols with ammonia to prepare the corresponding organic amines.

Enzyme cascade converting cyclohexanol into ε-caprolactone coupled with NADPH recycling using surface displayed alcohol dehydrogenase and cyclohexanone monooxygenase on E. coli.

SummaryThe application of enzymes as biocatalysts in industrial processes has great potential due to their outstanding stereo‐, regio‐ and chemoselectivity. Using autodisplay, enzymes can be immobilized on the cell surface of Gram‐negative bacteria such as Escherichia coli. In the present study, the surface display of an alcohol dehydrogenase (ADH) and a cyclohexanone monooxygenase (CHMO) on E. coli was investigated. Displaying these enzymes on the surface of E. coli resulted in whole‐cell biocatalysts accessible for substrates without further purification. An apparent maximal reaction velocity V MAX(app) for the oxidation of cyclohexanol with the ADH whole‐cell biocatalysts was determined as 59.9 mU ml−1. For the oxidation of cyclohexanone with the CHMO whole‐cell biocatalysts a V MAX(app) of 491 mU ml−1 was obtained. A direct conversion of cyclohexanol to ε‐caprolactone, which is a known building block for the valuable biodegradable polymer polycaprolactone, was possible by combining the two whole‐cell biocatalysts. Gas chromatography was applied to quantify the yield of ε‐caprolactone. 1.12 mM ε‐caprolactone was produced using ADH and CHMO displaying whole‐cell biocatalysts in a ratio of 1:5 after 4 h in a cell suspension of OD578nm 10. Furthermore, the reaction cascade as applied provided a self‐sufficient regeneration of NADPH for CHMO by the ADH whole‐cell biocatalyst.

Reductive amination of cyclohexanol/cyclohexanone to cyclohexylamine using SBA-15 supported copper catalysts

Amination of cyclohexanol was investigated in vapour phase over copper catalysts supported on mesoporous SBA-15. The different products identified during reductive amination of cyclohexanol reaction were cyclohexanone, cyclohexylamine, along with small amounts of N-Cyclohexylidinecyclohexylamine and dicyclohexylamine. Among several catalysts tested for the reductive amination, 5% Cu supported on SBA-15 exhibited better catalytic performance than other catalysts with 36% selectivity towards cylclohexylamine at 80% cyclohexanol conversion. The optimum reaction conditions employed to achieve the best catalyst performance were at 250 °C, 0.1 MPa of H2/NH3, TOS-10h. The active Cu sites, acidity of the catalyst, and effect of reaction parameters play a pivotal role in the reductive amination reaction. The prepared catalysts were characterized by XRD, BET, SEM, H2-TPR and NH3-TPD. The dispersion of Cu, particle size, and metal surface area (m2/g) calculated from pulse N2O decomposition method. TPR findings reveal the presence of substantially dispersed copper oxide species at lower loadings which is easily reducible than the bulk copper oxide species found at higher Cu loadings. The acidity measurements by NH3-TPD analysis suggest that the maximum acidic strength was obtained at 5 wt% copper on porous SBA-15, and decreased with Cu loadings. The catalytic properties are well in agreement with the findings of catalysts characterization.

CuO-ZnO-MgO as sustainable and selective catalyst towards synthesis of cyclohexanone by dehydrogenation of cyclohexanol over monovalent copper

• Cyclohexanol was converted into cyclohexanone by dehydrogenation. • Mixed metal oxide CuO-ZnO-MgO (1:1:1) as sustainable and robust catalyst. • The active species was monovalent copper. • No oxidant or coupling reaction was used in parallel. • Hydrogen as co-product can be used for different purposes. Cyclohexanone is the key ingredient for the manufacture of ε-caprolactam which is used for making Nylon 6. In this work, non-oxidative vapor phase dehydrogenation of cyclohexanol to cyclohexanone was carried out over monovalent copper using CuZnMg catalyst. The catalyst was prepared by co-precipitation method and characterized using different techniques, viz. XRD, FTIR, TPD, TPR, TGA, BET, SEM, EDX, and XPS. Cyclohexanol conversion of 55.0 % was resulted with 99.2 % selectivity of cyclohexanone at 260 ℃ with WHSV of 2.34 h −1 . Time on stream study (125 h) and catalyst reusability studies were performed to find that the catalyst was robust, stable and easily reusable. A reaction mechanism over surface Cu + is discussed and kinetics deduced.

Engineering the Distinct Structure Interface of Subnano-alumina Domains on Silica for Acidic Amorphous Silica-Alumina toward Biorefining.

Amorphous silica–aluminas (ASAs) are important solid catalysts and supports for many industrially essential and sustainable processes, such as hydrocarbon transformation and biorefining. However, the wide distribution of acid strength on ASAs often results in undesired side reactions, lowering the product selectivity. Here we developed a strategy for the synthesis of a unique class of ASAs with unvarying strength of Brønsted acid sites (BAS) and Lewis acid sites (LAS) using double-flame-spray pyrolysis. Structural characterization using high-resolution transmission electron microscopy (TEM) and solid-state nuclear magnetic resonance (NMR) spectroscopy showed that the uniform acidity is due to a distinct nanostructure, characterized by a uniform interface of silica–alumina and homogeneously dispersed alumina domains. The BAS population density of as-prepared ASAs is up to 6 times higher than that obtained by classical methods. The BAS/LAS ratio, as well as the population densities of BAS and LAS of these ASAs, could be tuned in a broad range. In cyclohexanol dehydration, the uniform Brønsted acid strength provides a high selectivity to cyclohexene and a nearly linear correlation between acid site densities and cyclohexanol conversion. Moreover, the concerted action of these BAS and LAS leads to an excellent bifunctional Brønsted–Lewis acid catalyst for glucose dehydration, affording a superior 5-hydroxymethylfurfural yield.

Dehydrogenation of Cyclohexanol to Cyclohexanone Over Nitrogen-doped Graphene supported Cu catalyst

In this study, the dehydrogenation of cyclohexanol to cyclohexanone over nitrogen-doped reduced graphene oxide (N-rGO) Cu catalyst has been reported. The N-rGO support was synthesized by chemical reduction of graphite oxide (GO). The synthesized N-rGO was used as a support to prepare the Cu/N-rGO catalyst via an incipient wet impregnation method. The as-prepared support and the Cu/N-rGO catalyst were characterized by FESEM, EDX, XRD, TEM, TGA, and Raman spectroscopy. The various characterization analysis revealed the suitability of the Cu/N-rGO as a heterogeneous catalyst that can be employed for the dehydrogenation of cyclohexanol to cyclohexanone. The catalytic activity of the Cu/N-rGO catalyst was tested in non-oxidative dehydrogenation of cyclohexanol to cyclohexanone using a stainless-steel fixed bed reactor. The effects of temperature, reactant flow rate, and time-on-stream on the activity of the Cu/N-rGO catalyst were examined. The Cu/N-rGO nanosheets show excellent catalytic activity and selectivity to cyclohexanone. The formation of stable Cu nanoparticles on N-rGO support interaction and segregation of Cu were crucial factors for the catalytic activity. The highest cyclohexanol conversion and selectivity of 93.3% and 82.7%, respectively, were obtained at a reaction temperature of 270 °C and cyclohexanol feed rate of 0.1 ml/min. Copyright © 2020 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Gas-phase selective oxidation of cyclohexanol to cyclohexanone over Au/Mg1-xCuxCr2O4 catalysts: On the role of Cu doping

The industrial production of cyclohexanone from cyclohexanol would benefit from a selective oxidation catalyst. Herein, Cu doping of MgCr2O4 supports for gold nanoparticles active in gas-phase oxidation of cyclohexanol was investigated. Mg1-xCuxCr2O4 exhibited spinel structures (x ≤ 0.25: MgCr2O4; x = 1: CuCr2O4) onto which 3–4 nm gold nanoparticles could be dispersed. Cu doping led to higher activity. During reaction, surface Cu2+ was reduced to Cu0, resulting in AuCu alloy formation. At low temperature, low-Cu-content catalysts (x ≤ 0.1) showed higher activity than high-Cu-content catalysts, likely because the AuCu alloy with highly diluted Cu was more active for the dehydrogenation step of cyclohexanol. However, Au/Mg0.99Cu0.01Cr2O4 and Au/Mg0.9Cu0.1Cr2O4 showed lower cyclohexanol conversion at high temperature than samples with high Cu content, because O2 activation involving Cu becomes rate-limiting. Stable cyclohexanol conversion and cyclohexanone selectivity were 99.1% and 90.2% (space-time yield of 266 gKetone gAu−1 h−1) for Au/Mg0.25Cu0.75Cr2O4 at 300 °C.

Performance of a Ni-Cu-Co/Al2O3 Catalyst on in-situ Hydrodeoxygenation of Bio-derived Phenol

The in-situ hydrodeoxygenation of bio-derived phenol is an attractive routine for upgrading bio-oils. Herein, an active trimetallic Ni-Cu-Co/Al2O3 catalyst was prepared and applied in the in-situ hydrodeoxygenation of bio-derived phenol. Comparison with the monometallic Ni/Al2O3 catalyst and the bimetallic Ni-Co/Al2O3 and Ni-Cu/Al2O3 catalysts, the Ni-Cu-Co/Al2O3 catalyst exhibited the highest catalytic activity because of the formation of Ni-Cu-Co alloy on the catalyst characterized by using X-ray powder diffraction (XRD), temperature programmed reduction (TPR), N2 physisorption, scanning electron microscope (SEM), and transmission electron microscope (TEM). The phenol conversion of 100% and the cyclohexane yield of 98.3% could be achieved in the in-situ hydrodeoxygenation of phenol at 240 °C and 4 MPa N2 for 6 h. The synergistic effects of Ni with Cu and Co of the trimetallic Ni-Cu-Co/Al2O3 catalyst played a significant role in the in-situ hydrodeoxygenation process of phenol, which not only had a positive effect on the production of hydrogen but also owned an excellent hydrogenolysis activity to accelerate the conversion of cyclohexanol to cyclohexane. Furthermore, the catalyst also exhibited excellent recyclability and good potential for the upgrading of bio-oils.

A Robust Au/ZnCr2O4 Catalyst with Highly Dispersed Gold Nanoparticles for Gas-Phase Selective Oxidation of Cyclohexanol to Cyclohexanone

Achieving uniformly dispersed and stable nanoparticles of gold on oxide supports is a challenge in heterogeneous catalysis. Here, we show that zincochromite (ZnCr2O4) is a promising support for obtaining high and stable gold dispersion. Despite a low surface area of ZnCr2O4, finely dispersed gold (∼3-4 nm particles) could be obtained by a simple deposition-precipitation method, pointing to strong gold-support interactions. Using a combination of XRD, XPS, SEM, TEM, HAADF-STEM, and IR spectroscopy, we confirmed that the calcination temperature of the ZnCr2O4 support had a substantial influence on the crystallinity, morphology, and acidic properties of thereof derived Au/ZnCr2O4 catalysts. Gold supported on a high-temperature (≥700 °C) calcined ZnCr2O4 support displayed the best catalytic performance in gas-phase oxidation of cyclohexanol to cyclohexanone, which is an important intermediate in the chemical industry. When calcined at 800 °C, the material did not show any sign of deactivation in a 90 h stability test, high cyclohexanol conversion (93%) and high cyclohexanone yield (91%) were achieved at 300 °C, with a space-time yield of 250 gproduct gAu-1 h-1. On the contrary, Au/ZnCr2O4 based on supports calcined at lower temperatures (≤600 °C) catalyzed side reactions such as cyclohexanol dehydration to cyclohexene (Lewis acid sites), which further oligomerized to coke deposits that deactivated the catalyst. The CO oxidation trends with respect to calcination temperature were inversed to those in cyclohexanol oxidation, showing that smaller gold particles and the presence of hydroxyls are favorable for CO oxidation to CO2. DFT calculations provided insight into the (electronic) nature of the strong interactions between Au and ZnCr2O4

A whole-cell process for the production of ε-caprolactone in aqueous media

Abstract e-Caprolactone is an industrially important intermediate produced in multi-10,000 ton scale annually with broad applications. We report on a whole-cell biocatalytic conversion of cyclohexanol to e-caprolactone using the combination of alcohol dehydrogenase (ADH) with two stability-improved variants (QM and M15) of the Baeyer-Villiger monooxygenase CHMO with a special focus on process development at the 200 mM scale. Influence of parameters such as volumetric mass transfer co-efficient, stirrer speed and catalytic loading (amount of E. coli whole-cells expressing ADH and CHMO) on the process efficiency were studied and optimised. This resulted in over 98% conversion, a product titer of 20 g L–1 and an isolated product amount of 9.1 g (80%). This corresponds to a space-time yield of 1.1 g L–1 h−1 and a reaction yield (mole of product per mole substrate) of 0.9. Comparing the two CHMO variants a significant difference in catalytic yield (weight of product to weight of catalyst; 0.6 vs 0.3) was observed without any inherent changes in the process. Hence, the reported process can accommodate in the future improved variants of the CHMO.

Tuning of the enzyme ratio in a neutral redox convergent cascade: A key approach for an efficient one-pot/two-step biocatalytic whole-cell system.

The efficiency of a versatile in vivo cascade involving a promiscuous alcohol dehydrogenase, obtained from a biodiversity search, and a Baeyer-Villiger monooxygenase was enhanced by the independent control of the production level of each enzyme to produce ε-caprolactone and 3,4-dihydrocoumarin. This goal was achieved by adjusting the copy number per cell of Escherichia coli plasmids. We started from the observation that this number generally correlates with the amount of produced enzyme and demonstrated that an in vivo multi-enzymatic system can be improved by the judicious choice of plasmid, the lower activity of the enzyme that drives the limiting step being counter-balanced by a higher concentration. Using a preconception-free approach to the choice of the plasmid type, we observed positive and negative synergetic effects, sometimes unexpected and depending on the enzyme and plasmid combinations. Experimental optimization of the culture conditions allowed us to obtain the complete conversion of cyclohexanol (16 mM) and 1-indanol (7.5 mM) at a 0.5-L scale. The yield for the conversion of cyclohexanol was 80% (0.7 g ε-caprolactone, for the productivity of 244 mg·L -1 ·h -1 ) and that for 1-indanol 60% (0.3 g 3,4-dihydrocoumarin, for the productivity of 140 mg·L -1 ·h -1 ).

Kinetic studies of reversible hydrogen storage over sodium phenoxide-cyclohexanolate pair in aqueous solution

Abstract With reduced dehydrogenation enthalpy change and reduced dehydrogenation temperature compared with its phenol-cyclohexanol pair, sodium phenoxide-cyclohexanolate pair developed recently is promising for large-scale energy storage and long-distance hydrogen transportation. In the present work, we investigate the kinetic behavior of the pair in the hydrogenation and dehydrogenation in water over three commercial catalysts. It is shown that 5% Ru/Al2O3 and 5% Pt/C perform well in the hydrogenation and dehydrogenation, respectively. Kinetic analyses show that the hydrogenation of sodium phenoxide is of first-order with respect to H2 pressure and zero-order to the concentration of sodium phenoxide in the presence of Ru/Al2O3 catalyst. >99% conversion of cyclohexanol and >99% selectivity to phenoxide can be achieved in the dehydrogenation catalyzed by Pt/C catalyst and in the presence of NaOH at 100 °C, where cyclohexanone was observed as an intermediate. According to the kinetic analysis, the hydrogenation of sodium phenoxide may undergo the hydrolysis and hydrogenation pathway. For the dehydrogenation, an intermediate, i.e., cyclohexanone, was detected and two possible pathways are proposed accordingly.

Oxidation of KA oil to caprolactone with molecular oxygen using N-hydroxyphthalimide-mediated Ce(NH4)2(NO3)6 catalyst

In traditional Baeyer-Villiger oxidation, peracids or hydrogen peroxide are usually adopted as the oxidants. When molecular oxygen is used as oxidant, the sacrificial agents are always indispensable, such as aldehydes that are transformed into cheap acids after reaction. In this work, KA oil (the industrial raw material, a mixture of cyclohexanol and cyclohexanone) has been oxidized to caprolactone by molecular oxygen using N-hydroxyphthalimide (NHPI) and cerium ammonium nitrate (CAN) as catalyst, in which the sacrificial agent is cyclohexanol, and it is converted into cyclohexanone, then into caprolactone rather than into byproducts. The selectivity of caprolactone was 98% with cyclohexanol conversion of 34% and it was still kept at 90% when the conversion reached to 46%. The mechanism investigation showed a bifunctional role of CAN, which performed both as a radical initiator for cyclohexanol oxidation and a Lewis acid for Baeyer-Villiger reaction. In the Baeyer-Villiger oxidation, a weak interaction between cerium and cyclohexanone was suggested by Fourier Transform Infrared Spectroscopy (FTIR), meanwhile, the active species generated from cerium and hydrogen peroxide was separated and characterized by FTIR. The detailed research also revealed an unusual effect between cerium and the Brønsted acid generated as a byproduct, which was critical for caprolactone synthesis.

Facile redbrick clay as splendid catalyst for selective dehydration of alcohols

Excellent catalytic activity of activated redbrick clay (ARB) for dehydration and highly selective conversion of cyclohexanol to cyclohexene and 1-phenylethanol to styrene is reported. The efficacy of the catalyst is compared with commercial catalysts, silica and α-Fe2O3, which performed poorly giving side products. Synergistic acidic properties and combinational Lewis and Bronsted acidic sites of ARB afforded superior performances relative to silica and α-Fe2O3 catalysts. Pyridine Fourier-transform-infrared spectra (FT-IR) and temperature-programmed desorption (NH3-TPD) measurements showed the presence of combinational Lewis and Bronsted acidic sites and a weak to mild acidic texture, which could facilitate favorable interaction between the ARB clay catalyst and the reactants (cyclohexanol and 1-phenylethanol). The physicochemical characteristics of ARB, commercial silica and α-Fe2O3 catalysts were investigated using X-ray diffraction, scanning electron microscopy, X-ray fluorescence, NH3-TPD, UV–visible diffuse reflectance spectroscopy, and pyridine FT-IR.

INTENSIFICATION OF THE CYCLOHEXANE LIQUID PHASE OXIDATION PROCESS

Liquid-phase oxidation of cyclohexane to cyclohexanol and cyclohexanone was studied in the absence of solvents under an air pressure of 0.5-5 MPa, in the temperature range 115-150 °C, catalyzed by N-hydroxyphthalimide (N-HPI). It was established for the first time that the use of N-HPI as a catalyst in place of the conventionally used metal salts of variable valence allowed a 2-3-fold increase in the conversion of the initial hydrocarbon and selectivity from 70-75 to 90%. The combined use of N-HPI with cobalt(II) acetate results in an additional increase in the conversion of cyclohexane by 30-40%, the selectivity of cyclohexanol and cyclohexanone formation to 94-97%, which seems to be due to the synergistic effect between the two components of the catalyst. The mechanism of catalytic oxidation of cyclohexane to cyclohexanol and cyclohexanone is discussed. It has been suggested that N-HPI plays a dual role in the oxidation of cyclohexane: it catalyzes the conversion of cyclohexane to cyclohexanol and cyclohexanone and, on the other hand, promotes the conversion of cyclohexanol to cyclohexanone, thereby substantially reducing the formation of adipic acid and its esters, by-products of the reaction, and increases selectivity of oxidation. This also explains the unusually high (1.3-1.5 : 1) ketone: alcohol ratio in the oxidation products of cyclohexane in the presence of N-HPI. The high selectivity of the formation of the desired products, the conversion of cyclohexane, the moderate temperature, the available catalyst, suggest that this method of oxidizing cyclohexane to cyclohexanol and cyclohexanone may be of interest for further practical use.