The synthesis of Co-doped SAPO-5 molecular sieve and its performance in the oxidation of cyclohexane with molecular oxygen

Silicoaluminophosphate（SAPO） molecular sieves doped with cobalt（Co-SAPO-5） were synthesized hydrothermally with different concentrations of Co.Each sample was characterized by X-ray diffraction,N2 adsorption-desorption,scanning electron microscopy,ultraviolet-visible spectroscopy,temperature-programmed desorption of NH3（NH3-TPD）,and infrared spectrascopy of adsorbed pyridine（Py-IR）.The results showed that Co was highly dispersed in the Co-SAPO-5 samples.In addition,a part of the Co content had been incorporated into the SAPO-5 framework,while the remainder existed on the surface as extra-framework Co.The surface areas of the Co-SAOP-5 samples were similar to the SAPO-5 sample.However,the pore volumes of the Co-SAOP-5 samples were lower than that of the SAOP-5 sample.As the concentration of Co increased,the pore volume gradually decreased because extra-framework cobalt oxide was present on the catalyst surface.NH3-TPD and Py-IR results revealed that the amount of Br（？）nsted acid and the total amount of acid for the Co-SAPO-5 samples were higher than that for the SAPO-5 sample.These values were also higher for samples with higher Co content.The catalytic activity of the Co-SAPO-5 samples was evaluated for the oxidation of cyclohexane with molecular oxygen.When Co was added to the SAPO-5 catalyst,the catalytic activity of the Co-SAPO-5 catalysts improved.In addition,the conversion of cyclohexane increased as the Co content in the Co-SAPO-5 catalysts increased.However,with a high conversion of cyclohexane（6.30%）,the total selectivity of cyclohexanone（K） and cyclohexanol（A） decreased sharply.The K/A ratio ranged from 1.15 to 2.47.The effects of reaction conditions（i.e.,reaction temperature,reaction time,initial oxygen pressure,and the catalyst amount） on the performance of the Co-SAPO-5 catalysts have also been measured.Furthermore,the stability of the Co-SAPO-5 catalyst was explored and found to be good for the selective oxidation of cyclohexane by molecular oxygen.

Solvent-free selective oxidation of cyclohexane with molecular oxygen over manganese oxides:Effect of the calcination temperature

The effects of calcination temperature on the physicochemical properties of manganese oxide catalysts prepared by a precipitation method were assessed by X-ray diffraction,N2 adsorption-desorption,X-ray photoelectron spectroscopy,H2 temperature-programmed reduction,O2 temperature-programmed desorption,and thermogravimetry-differential analysis.The catalytic performance of each of these materials during the selective oxidation of cyclohexane with oxygen in a solvent-free system was subsequently examined.It was found that the MnOx-500 catalyst,calcined at 500 °C,consisted of a Mn2O3 phase in addition to Mn5O8 and Mn3O4 phases and possessed a low surface area.Unlike MnOx-500,the MnOx-400 catalyst prepared at 400 °C was composed solely of Mn3O4 and Mn5O8 and had a higher surface area.The pronounced catalytic activity of this latter material for the oxidation of cyclohexene was determined to result from numerous factors,including a higher concentration of surface adsorbed oxygen,greater quantities of the surface Mn4＋ ions that promote oxygen mobility and the extent of O2 adsorption and reducibility on the catalyst.The effects of various reaction conditions on the activity of the MnOx-400 during the oxidation of cyclohexane were also evaluated,such as the reaction temperature,reaction time,and initial oxygen pressure.Following a 4 h reaction at an initial O2 pressure of 0.5 MPa and 140 °C,an 8.0% cyclohexane conversion and 5.0% yield of cyclohexanol and cyclohexanone were achieved over the MnOx-400 catalyst.In contrast,employing MnOx-500 resulted in a 6.1% conversion of cyclohexane and 75% selectivity for cyclohexanol and cyclohexanone.After being recycled through 10 replicate uses,the catalytic activity of the MnOx-400 catalyst was unchanged,demonstrating its good stability.

Synthesis of cerium-doped MCM-48 molecular sieves and its catalytic performance for selective oxidation of cyclohexane

Cerium-doped MCM-48 molecular sieves were synthesized hydrothermally and characterized by X-ray diffraction, nitrogen adsorption, transmission electron microscope, FT-IR spectroscopy, UV-visible spectroscopy, and Raman spectroscopy. The results showed that all the samples held the structure of MCM-48, and Ce could enter the framework of MCM-48. However, when Ce/Si molar ratio in the sampies was high （0.04 or 0.059）, there were CeO2 crystallites as secondary phase in the extraframework of MCM-48. Ce-doped MCM-48 was a very efficient catalyst for the oxidation of cyclohexane in a solvent-free system with oxygen as an oxidant. In the conditions of 0.5 MPa 02 and 413 K for 5 h, the conversion of cyclohexane was 8.1% over Ce-MCM-48-0.02, the total selectivity of cyclohexanol and cyclohaxnone was 98.7%. With an increase of Ce content, the conversion of cyclohexane and the selectivity to cyclohexanol decreased somewhat, but the selectivity to cyclohexanone increased.

Highly efficient cobalt-doped carbon nitride polymers for solvent-free selective oxidation of cyclohexane

Selective oxidation of saturated hydrocarbons with molecular oxygen has been of great interest in catalysis, and the development of highly efficient catalysts for this process is a crucial challenge. A new kind of heterogeneous catalyst, cobalt-doped carbon nitride polymer(g-C_3N_4),was harnessed for the selective oxidation of cyclohexane. X-ray diffraction, Fourier transform infrared spectra and high resolution transmission electron microscope revealed that Co species were highly dispersed in g-C_3N_4 matrix and the characteristic structure of polymeric g-C_3N_4 can be retained after Co-doping, although Co-doping caused the incomplete polymerization to some extent. Ultraviolet-visible, Raman and X-ray photoelectron spectroscopy further proved the successful Co doping in g-C_3N_4 matrix as the form of Co(Ⅱ)-N bonds. For the selective oxidation of cyclohexane, Co-doping can markedly promote the catalytic performance of g-C_3N_4 catalyst due to the synergistic effect of Co species and gC_3N_4 hybrid. Furthermore, the content of Co largely affected the activity of Co-doped g-C_3N_4 catalysts, among which the catalyst with 9.0 wt%Co content exhibited the highest yield(9.0%) of cyclohexanone and cyclohexanol, as well as a high stability. Meanwhile, the reaction mechanism over Co-doped g-C_3N_4 catalysts was elaborated.

New insights for the catalytic oxidation of cyclohexane to K-A oil

Au-based catalysts have been reported to be active in the cyclohexane oxidation to K-A oil, but they showed some limitiations in terms of productivity, selectivity and required reaction conditions. The possibility to overcome some of these limits has been explored coupling Au with Cu, which can be suitable for undergoing the electron-switch in the initial step of the cyclohexane oxidation. Hence, a bimetallic 2 wt% Au Cu/Al_(2)O_(3) catalyst was tested in the oxidation of cyclohexane, working at mild conditions of 120 ℃ and 4 bar of O_(2). The combination of the catalyst with a very small amount of benzaldehyde used as cheaper and non-toxic radical initiator allowed to obtain a very high productivity of cyclohexanol and cyclohexanone(45 mmol*m L/mgmet*h) with a selectivity of 94%. Moreover, comparing the catalysed reaction with the non-catalysed one, the role of the catalyst has been disclosed.

Exploring the Low-Temperature Oxidation Chemistry of Cyclohexane in a Jet-Stirred Reactor:an Experimental and Kinetic Modeling Study

We report the investigation on the low-temperature oxidation of cyclohexane in a jet-stirred reactor over 500-742 K. Synchrotron vacuum ultraviolet photoionization mass spectrometry （SVUV-PIMS） was used for identifying and quantifying the oxidation species. Major products, cyclic olefins, and oxygenated products including reactive hydroperoxides and high oxygen compounds were detected. Compared with n-alkanes, a narrow low-temperature window （-80 K） was observed in the low-temperature oxidation of cyclohexane. Besides, a kinetic model for cyclohexane oxidation was developed based on the CNRS model [Combust. Flame 160, 2319 （2013）], which can better capture the experimental results than previous models. Based on the modeling analysis, the 1,5-H shift dominates the crucial isomerization steps of the first and second O2 addition products in the low-temperature chain branching process of cyclohexane. The negative temperature coefficient behavior of cyclohexane oxidation results from the reduced chain branching due to the competition from chain inhibition and propagation reactions, i.e. the reaction between cyclohexyl radical and O2 and the de- composition of cyclohexylperoxy radical, both producing cyclohexene and HO2 radical, as well as the decomposition of cyclohexylhydroperoxy radical producing hex-5-en-l-al and OH radical.

Estimation of Kinetic Parameters for Autocatalytic Oxidation of Cyclohexane Based on a Modified Adaptive Genetic Algorithm

A modified genetic algorithm of multiple selection strategies, crossover strategies and adaptive operator is constructed, and it is used to estimate the kinetic parameters in autocatalytic oxidation of cyclohexane. The influences of selection strategy, crossover strategy and mutation strategy on algorithm performance are discussed. This algorithm with a specially designed adaptive operator avoids the problem of local optimum usually associated with using standard genetic algorithm and simplex method. The kinetic parameters obtained from the modified genetic algorithm are credible and the calculation results using these parameters agree well with experimental data. Furthermore, a new kinetic model of cyclohexane autocatalytic oxidation is established and the kinetic parameters are estimated by using the modified genetic algorithm.

Ship-in-bottle synthesis of NaY zeolite encapsulated Cosalen complex and its catalytic performance for cyclohexane oxidation

N, N＇-bis （salicylidene） ethylenediiminocobalt （Cosalen） was encapsulated into microporous NaY zeolite via the technique of ＂ship-in-bottle＂. The encapsulated complex （Cosalen-NaY） was characterized by Fourier-transform infrared spectrum, ultraviolet-visible spectrum, Brunaner-Emmett-Teller surface areas, X-ray diffraction, thermogravimetry-differential thermal analysis and scanning electron microscope. The reaction of cyclohexane oxidation using oxygen was chosen to investigate the catalytic performance of Cosalen-NaY, and the effects of oxygen pressure, temperature and reaction time were also studied. The results show that Cosalen complex is encapsulated into the supercage of the zeolite and the structure of NaY zeolite remains integrity and the thermal stability of Cosalen is greatly enhanced after encapsulation. Cosalen-NaY shows the better activity in the oxidation of cyclohexane without reductant and solvent. The conversion of cyclohexane is up to 13.4% at 150 ℃ for 3 h under oxygen pressure of 0.85 MPa, with the higher total selectivity to cyclohexanol, cyclohexanone, cyclohexyl hydroperoxide （CHHP） and acid （79.2%） than the neat complex （55.5%）. NaY zeolite cartier maybe contributes to the results. There is no obvious induction period to initiate the reaction; furthermore, the amount of CHHP among the products is small, which indicates that the Cosalen-NaY has the strong ability to accelerate the decomposition of CHHP. Recycling tests show that the hybrid material can be used repeatedly with a negligible loss of active sites.

Catalytic Oxidation of Cyclohexane over ZSM-5 Catalyst in N-alkyl-N-methylimidazolium Ionic Liquids

Heterogeneous oxidation of cyclohexane by tert-butyl hydroperoxide (TBHP) was carried out over ZSM-5 catalysts with different Si/Al ratios in ionic liquids and organic molecular solvents. Higher yield and selec-tivity of the desired products were found in ionic liquids than in molecular solvents. The conversion of cyclohexane exhibits a decrease from 15.8% to 10.8% with the increase of Si/Al ratio of the HZSM-5 catalyst, and all the cata-lysts exhibit good selectivity of monofunctional oxidation products at around 97%. The activity of catalyst is found strongly dependent on the alkyl chain length of ionic liquid.

Solution-combustion Synthesized Nano-pellet α-Al_(2)O_(3) and Catalytic Oxidation of Cyclohexane by Its Supported Cobalt Acetate

Nano-pelletα-Al_(2)O_(3) was prepared using aluminum nitrate as precursor and urea as fuel by a fast method of solution combustion synthesis.The formation of the nano material was dependent on the molar ratio of fuel/oxidant,calcination temperature,and foreign metallic ions.The prerequisite conditions of the formation were a suitable fuel/oxidant molar ratio larger than two and calcination temperature higher than 673 K.Foreign ions,Ce^(4+) or Co^(2+),hindered this formation via promoting the generation of stable penta-coordinated Al^(3+) ions due to strong interaction with alumina,were revealed by ^(27)Al NMR spectra.Such Al^(3+) ions were recognized as a critical intermediate state for the phase transformation of alumina and their presence deterred the transformation.The nano-pellet morphology of the product demonstrated a specific surface area of 69 m^(2)/g,of which the external surface area occupied 59 m^(2)/g.It was found that the supported cobalt acetate on such nano-pellets existed as nanoparticles attached to the external surface,evidenced by the TEM characterization.The prepared catalyst could efficiently catalyze the selective oxidation of cyclohexane under the reaction condition of pressure under 0.8 MPa,temperature at 373 K,and time for 4 hours.The conversion of the reaction achieved up to 7.9%;while the cyclohexanone selectivity was 42.7%and the cyclohexanone and cyclohexanol selectivity was 91.6%.This catalytic performance recommends the supported cobalt acetate on the inert nano-pellet a-Al_(2)O_(3) as a promising catalyst for the selective oxidation of cyclohexane.

Solvent-free partial oxidation of cyclohexane to KA oil over hydrotalcitederived Cu-MgAlO mixed metal oxides

A highly efficient and stable hydrotalcite-derived Cu-MgAlO catalyst was developed for the partial oxidation of cyclohexane with molecular oxygen.The physical–chemical properties of Cu-MgAlO catalysts were studied,and the results indicated that the copper component had been successfully introduced into the hydrotalcite unit layer structure.The catalytic reaction results showed that copper as the active species could activate CAH bond and effectively promote the decomposition of cyclohexyl hydroperoxide(CHHP)to the mixture of cyclohexanol and cyclohexanone(KA oil).8.3%of cyclohexane conversion and 82.9%of selectivity for KA oil were obtained over 9%Cu-MgAlO catalyst at 150℃with 0.6 MPa of oxygen pressure for 2 h.Especially,its catalytic performance was still stable after five runs.

Studies of Cyclohexane Catalytic Oxidation Processes over Titanium Silicate-1 Zeolite

The catalytic oxidation processes for cyclohexane/H_2O_2/acetone system overthe TS-1 zeolite was studied. Study results have revealed that the cyclohexane conversion was 27%after the reaction proceeded at 100℃ for 2 hours at a cyclohexane/H_2O_2 molar ratio of 0.8. Thecyclohexanol/cyclohexanone molar ratio was 1.3 along with a certain amount of organic acids andesters, the formation of which was closely associated with the oxidation of reaction solvent anddeep oxidation of cyclohexanone and cyclohexanol contained in the reaction products. With respect tothe catalytic oxidation of cyclohexane/H_2O_2 system the selection of appropriate solvent wascritically important.

XPS,Chemical Trapping, and DRFTIR Study on Mechanism of By-Products Formation in Selective (AMM)Oxidation of Propylene on MoO_3 and γ-Bi_2MoO_6

XPS and chemical trapping experments with H2, NH3, and CH3I as trapping agents were carried out for studying the adsorption of propylene over MoO3 or r-Bi2MoO6. The results show that the fragmentation of carbon chain takes place during the adsorption of propylene through breaking C -C double bond and C-C bond on Mo2+ and the adjacent lattice oxygen, leading to formation of the oxygen- or nitrogen-containing by-products of C1 and C2 species. Diffuse-Reflection Fourier Transform Infrared (DRFTIR) Spectroscopy was used to study the surface species formed during the chemisorption and reaction of propylene over y-Bi2MoO6 at a lower temperature. The results that C1, C2 adspecies were detected by DRFTIR at 175℃ are consistent with the results of XPS and chemical trapping experiments, whlle the results at 50℃ Grasselli et al.

Photoelectrocatalytic Oxidation of Ethinylestradiol on a Ti/TiO₂Electrode: Degradation Efficiency and Search for By-Products

The degradation of ethinylestradiol (EE, an orally bio-active estrogen) in an aqueous-methanolic solution using a Ti/TiO2 thin-film electrode and UV radiation (a photoelectrocatalytic system) was evaluated. Hence, HPLC/UV analysis shows that EE (at 0.34 mmol) is totally consumed after 30 minutes of exposure to the photoelectrocatalytic system in the presence of Na2SO4 (0.1 mol·L-1) and with an applied bias potential of +1.0 V versus the Ag/AgCl reference electrode. Moreover, monitoring by direct infusion electrospray ionization mass spectrometry (ESI-MS) and SPME-GC/ MS (solid phase microextraction coupled with gas chromatography-mass spectrometry) reveals that apparently no degradation products are formed under these conditions. Hence, this study demonstrates that the photoelectrocatalytic system can be efficiently used to promote the complete degradation (and likely mineralization) of this hormone under these conditions.

Copper Tetrahydrosalen Complex Encapsulated in Zeolite Y:an Effective Heterogeneous Catalyst for the Oxidation of Cycloalkanes

A new heterogeneous catalyst, copper tetrahydrosalen complex encapsulated in zeolite Y （denoted as Cu[H4]salen/Y） has been developed with flexible ligand method, and characterized by FTIR, DR UV-Vis spectroscopy, N2 adsorption/desorption at -196℃. This catalyst behaved like a bio-mimic enzyme, and exhibited much higher activity for the oxidation of cycloalkanes than Cusalen/Y prepared with the same method. The effects of the reaction conditions on the catalytic performance were investigated.

Construction of multifunctional lanthanum manganese mixed nanoparticles mediated by ionic liquids for selective aerobic oxidation of cyclohexane

Selective oxidation of alkanes to produce highvalue chemicals is an essential strategy and means to realize efficient utilization of resources.In this work,a strategy of lanthanum manganese mixed metal oxides(LMMO)regulated via a facile ionic liquid(IL)-assisted hydrothermal method was proposed to construct the multifunctional catalysts,which exhibited excellent catalytic performance in the selective aerobic oxidation of cyclohexane.An 8.9%cyclohexane conversion with 90%KA oi(cyclohexanol and cyclohexanone)selectivity was achieved over the optimal LMMO catalyst under mild conditions.The effects of anion type,carbon chain length and concentration of ILs on the structure and properties of catalysts were investigated through various characterizations,indicating the structure-directing and template effect of ILs on the multifunctional catalysts.The formation of self-assembled spherical nanoparticles followed the"dissolution-nucleation-proliferation"mechanism with the introduction of 1-butyl-3-methylimidazolium hydrogen sulfate,ascribing the synergistic effect between the microenvironment of ILs and the hydrothermal environment.Importantly,the high reactive oxygen concentration redox capacity,and suitable basic sites of LMMO catalysts mediated by ILs enhance the activation of C-H bonds and molecular oxygen,simultaneously influencing the adsorption and desorption of the substrate.A comprehensive understanding of the high KA oil selectivity and radical reaction mechanism was elucidated based on in situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS)and radical trapping experiments.The recycling and regeneration experiments further illuminated that the removal of adsorbed cyclohexanone acting on the LMMO catalyst was the key to achieve high KA oil selectivity.

Highly dispersive tetrahedral vanadium species on pure silica ZSM-12 zeolite boosting the selective oxidation of cyclohexane into cyclohexanone

The selective oxidation of cyclohexane is a promising green route for the production of KA oil(cyclohexanol and cyclohexanone),but remains a huge challenge to design high-performing heterogeneous catalysts under mild conditions.Herein,a pure silica ZSM-12(MTW topology)zeolite was applied as the support to immobilize highly dispersive tetrahedrally coordinated vanadium(V)species and the constructed catalyst 1%V/SZ-12 exhibited high efficiency in the fast and selective oxidation of cyclohexane into cyclohexanone with H_(2)O_(2).The reaction completed within 30 s,affording the selectivity of 99%towards cyclohexanone and the extremely high turnover frequency(TOF)of 5,891 h^(-1).1%V/SZ-12 was facilely reused with stable activity and feasibly extended to the oxidation of various cyclohexane derivatives.The one-dimensional 12-membered ring microchannels contributed to the formation and accessibility of tetrahedrally coordinated high valent V5+species as the robust active centers,which activated H_(2)O_(2) to generate V–O–O·,the active oxygen species for the electrophilic attack on cyclohexane to produce cyclohexanone as the sole product.

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 CoCl_(2),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.

Cobalt-nitrogen co-doped porous carbon sphere as highly efficient catalyst for liquid-phase cyclohexane oxidation with molecular oxygen and the active sites investigation

The selective oxidation of cyclohexane to cyclohexanone and cyclohexanol(KA oil)is a challenging issue in the chemical industry.At present the industrial conversion of cyclohexane to cyclohexanone and cyclohexanol is normally controlled at less than 5%selectivity.Thus,the development of highly active and stable catalysts for the aerobic oxidation of cyclohexane is necessary to overcome this low-efficiency process.Therefore,we have developed a cobalt-nitrogen co-doped porous sphere catalyst,Co-NC-x(x is the Zn/Co molar ratio,where x=0,0.5,1,2,and 4)by pyrolyzing resorcinol-formaldehyde resin microspheres.It achieved 88.28%cyclohexanone and cyclohexanol selectivity and a cyclohexane conversion of 8.88%under Co-NC-2.The results showed that the introduction of zinc effectively alleviated the aggregation of Co nanoparticles and optimized the structural properties of the material.In addition,Co0 and pyridinic-N are proposed to be the possible active species,and their proportion efficiently increased in the presence of Zn^(2+)species.In this study,we developed a novel strategy to design highly active catalysts for cyclohexane oxidation.

Advances and perspectives in catalysts for liquid-phase oxidation of cyclohexane

The latest progress and developments in catalysts for the oxidation of cyclohexane are reviewed. Catalytic systems for the oxidation of cyclohexane including metal supported, metal oxides, molecular sieves, metal substituted polyoxometalates, photocatalysts, orga nocatalysts, Gif systems, metal-organic catalysts and metalloporphyrins are discussed with a particular emphasis on metalloporphyrin catalytic systems. The advantages and disadvantages of these methods are summarized and analyzed. Finally, the development trends in the oxidation technology of cyclohexane are examined.