Selectivity Of Cyclohexanol Research Articles

Immobilization of metalloporphyrin on organosilicon microsphere mixed with ceria as a new catalyst for oxidation of cyclohexane

In this study, cobalt tetraphenylporphyrin was immobilized through amide bond on organosilicon microsphere mixed with ceria. The catalysts were characterized and the catalytic performance was investigated. The results show that the catalysts are nanoparticles with average sizes of 30 nm and organosilicon microsphere is mixed with ceria. In addition, the catalysts exhibit excellent catalytic performance for selective oxidation of cyclohexane by molecular oxygen without solvent in a sealed autoclave reactor, due to the cooperative effect among the metalloporphyrin, organosilicon microsphere and ceria. The conversion of cyclohexane and the selectivity of cyclohexanol + cyclohexanone reached 14.21% and 54.6%, respectively. After repeated reuse, the conversion of cyclohexane and the selectivity of cyclohexanol + cyclohexanone were still kept at about 13.1% and 61.9%, respectively.

Experimental Study on Cyclohexane by Catalytic Oxidation Using H<sub>2</sub>O<sub>2</sub>/Ferrous Sulfate

Catalytic oxidation of cyclohexane to cyclohexanone and cyclohexanol using hydrogen peroxide over ferrous sulfate catalyst at atmospheric condition was studied. Effect of the solvent volume, catalyst amount, hydrogen peroxide volume, reaction temperature, reaction time on reaction was investigated. Results showed that using 10 mL of acetone, 0.02 g of a ferrous sulfate and 0.5 mL of hydrogen peroxide at thereaction temperature of 80 °C for 8 h, the conversion of cyclohexane was 35.35%, the total selectivity of cyclohexanone and cyclohexanol was 94.06%.

Self-assembly preparation of Au/SiO2 catalyst and its catalysis for cyclohexane oxidation with air

Au/SiO2 catalysts were prepared by self-assembly technique and characterized by EDS, XRD, XPS, AAS and N2 adsorption/desorption. They were found to be very efficient catalysts for the selective oxidation of cyclohexane with air in the absence of any solvent or promoter. The influences of Au loading, reaction temperature, reaction pressure and reaction time on the catalytic activity were explored in detail. Under suitable reaction conditions, the conversion of cyclohexane and total selectivity of cyclohexanone and cyclohexanol were up to ~10 and ~92%, respectively.

Selective Oxidation of Cyclohexane Catalyzed by Metallo-Deuteroporphyrins in Homogeneous Solution

To search for the efficient biomimetic catalysts for the oxidation of hydrocarbon,cobalt deuteroporphyrin [Co(DPDME)] was used as catalyst for the oxidation of cyclohexane with air.The effects of reaction temperature,pressure of air,the catalyst amount and different complexes were evaluated.The experiment results show that Co(DPDME) is more effective than the others,and the optimum reaction conditions for the oxidation of cyclohexane are:c=0.015 mmol/L,reaction temperature 423 K,pressure of air 0.8 MPa,reaction time 5 h.Under the optimum conditions,the conversion rate of cyclohexane could reaches to 18.2%,the total selectivity of cyclohexanol and cyclohexanone is 87.4%.The temperature has much more influence on the catalytic reaction.Although the stability of Co(DPDME) was reduced when the temperature is higher than 443 K,the turnover number reaches 66 646.We also discussed the possible reaction path of Co(DPDME)-catalyzed oxidation of cyclohexane with oxygen.

Catalytic oxidation of cyclohexane over Ti–Zr–Co catalysts

Ti–Zr–Co alloys have been fabricated and characterized, and their catalytic performance was discussed for the oxidation of cyclohexane with oxygen under solvent-free condition. The icosahedral quasicrystalline phase (I-phase)-forming ability of Ti–Zr–Co alloys with different compositions was discussed, and it was confirmed that I-phase could be formed as a dominating phase at the Ti-rich composition region from Ti 53Zr 27Co 20 to Ti 75Zr 5Co 20 in as-cast alloys. The composition and microstructure of Ti–Zr–Co alloys present crucial influences on its catalytic activity and selectivity in the oxidation of cyclohexane. The influences of some reaction parameters such as temperature, reaction time, and catalyst amounts were also investigated. Ti 70Zr 10Co 20 alloy containing quasicrystal microstructure showed good catalytic performance with a 6.8% conversion of cyclohexane and 90.4% selectivity of cyclohexanol and cyclohexanone. It behaves as an efficient heterogeneous catalyst for the oxidation of cyclohexane and could be recycled five times without loss in activity and selectivity.

Magnetic CoFe 2O 4 nanocrystal: A novel and efficient heterogeneous catalyst for aerobic oxidation of cyclohexane

Magnetic nanocrystalline spinel-type cobalt ferrite complex oxides were prepared by a simple sol–gel auto-combustion method at five different molar ratios of Co II to Fe III (1:4.0, 1:2.8, 1:2.0, 1:1.5, and 1:1.1) and characterized by X-ray diffractometry (XRD), Fourier transform infrared spectrophotometry (FT-IR) and transmission electron microscopy (TEM). Their catalytic performance was evaluated in the oxidation of cyclohexane with oxygen as oxidant in the presence of neither solvents nor reducing agents. It has been revealed that the catalysts had high catalytic activities for heterogeneous oxidation of cyclohexane. Especially, when pure CoFe 2O 4 was used as catalyst; excellent results with turnover number of 288 and 92.4% selectivity for cyclohexanone and cyclohexanol was obtained under 1.6 MPa of initial oxygen pressure at 418 K after 6.0 h of reaction. The influences of initial oxygen pressure, reaction temperature, reaction time, and free-radical initiator on the oxidation of cyclohexane over CoFe 2O 4 were investigated. The catalyst can be easily separated by an external magnet and no obvious loss of activity was observed when reused in five consecutive runs. CoFe 2O 4 was proved to be also efficient for oxidation of linear alkanes.

Cyclohexane oxidation catalyzed by manganese oxide octahedral molecular sieves—Effect of acidity of the catalyst

Oxidation of cyclohexane is an important industrial process, its oxidation products, cyclohexanol and cyclohexanone are raw materials for adipic acid and caprolactam synthesis. Acid exchanged cryptomelane type manganese oxide octahedral molecular sieves (H-K-OMS-2) was used for liquid phase oxidation of cyclohexane with t-butyl hydroperoxide as an oxidant. The H + form of K-OMS-2 was synthesized by ion-exchange of K-OMS-2 with concentrated nitric acid. H-K-OMS-2 has been found to be an efficient catalyst for the oxidation of cyclohexane with a high conversion (∼60%). More than 90% selectivity for cyclohexanol and cyclohexanone was obtained. A turn over number (TON) of 73 was obtained in 24 h at 80 °C and if we consider only contributions of acidic manganese sites then the TON is 287. Effect of increase in number of acid sites of the K-OMS-2 was correlated with the increase in conversion. The reactions were carried out in a semi-batch reactor at 80 °C using acetonitrile as solvent. Effects of solvent, temperature, and amount of t-butyl hydroperoxide on conversion and selectivity were studied.

Selective aerobic oxidation of cyclohexane catalyzed by metallodeuteroporphyrin-IX-dimethylester

Metallodeuteroporphyrin-IX-dimethylesters of Cu(II), Co(II), Ni(II) and Zn(II) were used successfully for the first time to catalyze the aerobic oxidation of cyclohexane without any co-catalysts and solvents. The reaction was carried out at 150 °C under 0.8 MPa and all the four metallodeuteroporphyrins acted as efficient catalysts. Among them, deuteroporphyrin-IX-dimethylester Co(II) had the best catalytic activity with enhanced cyclohexane conversion of 18.6%, selectivity of cyclohexanol and cyclohexanone of 84.6% and cyclohexane turnover number of 8.5 × 104. The cyclohexane conversion and catalysis turnover number for deuteroporphyrin-IX-dimethylester Co(II) were about 10 times of those for tetraphenylporphyrin Co(II), respectively.

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 samples was high (0.04 or 0.059), there were CeO 2 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 O 2 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.

Rational oxidation of cyclohexane to cyclohexanol, cyclohexanone and adipic acid with air over metalloporphyrin and cobalt salt

A systematic study on the effect of a catalyst on the aerobic oxidation of cyclohexane was carried out using cobalt isooctanoate, metalloporphyrin p- ClTPPCo and [p- ClTPPFe ]2 O as catalysts. The results showed that the metalloporphyrin-catalyzed system performed better than the traditional cobalt salt ( Co isooctanoate) in terms of both the reaction conversion and the selectivity of cyclohexanol and cyclohexanone (KA oil). More importantly, we discovered that bisironporphyrin complex, which was traditionally considered to be either non-active or not-so-active for hydrocarbon oxidation, excelled at 155°C, achieving high selectivity for KA oil (80%) and good reaction conversion (13.8%). This result is in sharp contrast to earlier results by others. Meanwhile, the production of adipic acid was also increased and good selectivity of adipic acid among the by-products was also obtained. Our study suggested that [p- ClTPPFe ]2 O catalyzed aerobic oxidation could be used to produce adipic acid in addition to KA oil. Some mechanistic rationales were proposed to explain the superior performance of the [p- ClTPPFe ]2 O catalyst based on its unique structural and chemical properties.

Aerobic oxidation of cyclohexane with γ-alumina supported metallophthalocyanines in the gas phase

Abstract Unsubstituted phthalocyanines of Co, Fe and Mn supported on γ-alumina were synthesized and characterized with UV–vis and IR spectroscopic techniques. Catalytic activities of the supported phthalocyanines for oxidation of cyclohexane to cyclohexanol and cyclohexanone by air were studied in the gas phase in the absence of solvents and reducing agents. These metallophthalocyanines (MPc) supported on γ-alumina were effective catalysts in a temperature range of 300–400 °C at 1 atm of air. Under these reaction conditions, the order of catalytic activities is as follows: CoPc/γ-alumina > FePc/γ-alumina > MnPc/γ-alumina. When the reaction was catalyzed with γ-alumina without any phthalocyanines, the reaction yield and conversion were reduced considerably compared to those of supported γ-alumina. With 10% CoPc supported on γ-alumina and under our experimental conditions, the conversion percent of cyclohexane is 32.6% with 37.3% selectivity of cyclohexanol + cyclohexanone and 17.4% cyclohexene at 340 °C. To achieve higher conversion of cyclohexane and better selectivity toward cyclohexanone + cyclohexanol, factors such as type and percentage of the metallophthalocyanine, reaction temperature and space velocity were studied, and optimized conditions were investigated.

Photocatalytic air oxidation of cyclohexane in CH 2Cl 2–C 6H 12 mixtures over TiO 2 particles : An attempt to rationalize the positive effect of dichloromethane on the yields of valuable oxygenates

Product selectivity and yields of cyclohexanol and cyclohexanone formation in the photocatalytic air oxidation of cyclohexane on TiO 2 particles in the presence of dichloromethane were determined at 303 ± 5 nm and 4.35 nEinstein cm −2 s −1, as a function of cyclohexane molar fraction, x. Apparent initial photonic efficiencies, ξ o x , for total monooxigenated products (cyclohexanol + cyclohexanone) ranged from 19 to 51% depending on solvent composition, attaining a maximum for an equimolar mixture of CH 2Cl 2–C 6H 12. Singlet oxygen, 1O 2, formation was determined by the specific 2,2,6,6-tetramethyl-4-piperidone EPR assay. Yields of 1O 2, correlate with the amount of cyclohexanol detected in the mixtures, strongly suggesting that cyclohexanol is formed through the recombination of cyclohexylperoxy radicals which is favoured in the more polar media. Simultaneous determinations of chloride yields provide direct evidence of the active participation of dichloromethane in the photocatalytic system. A mechanism is proposed to account for the observed increment in the apparent efficiencies and the selectivity changes.

Catalysis of structure-like macromolecules supported manganese tetraphenylporphyrin for cyclohexane oxidation

Manganese tetraphenylporphyrin (Mn TPP) has been successfully supported on chitosan (CTS), chitin (CTN) and cellulose (CLS) by means of physical adsorption, and they are characterized by UV–Vis spectroscopy. The supported catalysts exhibit enhanced activity and effective recycle (except for Mn TPP/CLS) for oxidation of cyclohexane in the presence of air as oxidant. Both Mn TPP/CTS and Mn TPP/CTN show higher selectivity for cyclohexanone and cyclohexanol, whereas Mn TPP/CLS shows lower selectivity. The kind of support influences the catalytic activities and the selectivity for the supported catalysts. Appearance of the catalytic differences is attributed to the presence of the microenvironment differences for the supports.

Vapour phase hydrogenation of phenol over Pd/C catalysts: A relationship between dispersion, metal area and hydrogenation activity

A series of palladium supported on activated carbon catalysts, with Pd varying from 0.5 to 6.0wt%, were prepared via wet impregnation method using PdCl2·xH2O as a precursor salt. The dried samples were further reduced at 573K in hydrogen and characterized by CO adsorption at room temperature in order to determine the dispersion, metal area and particle size. The catalysts were tested for vapour phase phenol hydrogenation in a fixed-bed all glass micro-reactor at a reaction temperature of 453K under normal atmospheric pressure. The decrease in metal surface area as well as dispersion with corresponding increase in turn-over frequency (TOF) against palladium loadings suggest the unusual inverse relationship that exist between Pd dispersion and phenol hydrogenation activity over Pd/carbon catalysts. The stability of TOF at larger crystallite size indicates that phenol hydrogenation is less sensitive reaction especially beyond 3wt% of Pd content. It is evident from the results that structural properties of the catalysts strongly influence the availability of Pd atoms on the surface for CO chemisorption and hence for phenol hydrogenation. A comparison between selectivity and product yield of the reaction against overall phenol conversion indicates that changes in reaction selectivity for cyclohexanone or cyclohexanol is independent of phenol conversion level and either of the product is not formed at the cost of another. The stability of the catalysts with reaction time suggests that coke formation on the surface of the catalyst is less significant and the formation of cyclohexanone remains almost total even at higher reaction temperatures.

Cyclohexane oxidation catalyzed by mononuclear iron(III) complexes

In this work, we present the oxidation of cyclohexane catalyzed by a family of mononuclear iron(III) complexes: [Fe(BMPA)Cl 3] 1, [Fe(MPBMPA)Cl 3] 2, [Fe(PBMPA)Cl 2] 3 and [Fe(PABMPA)Cl 2](ClO 4) 4 using hydrogen peroxide or tert-butyl hydroperoxide as oxidant, in acetonitrile solution. These complexes were able to oxidize the cyclohexane into cyclohexanol and cyclohexanone with good yields. It was also possible to characterize by gas chromatography and mass spectrometry the by-products, cyclohexyl hydroperoxide and tert-butyl cyclohexyl peroxide. Adipic acid (AA) was also formed in the reaction and it was determined by titration. The reactions with hydrogen peroxide exhibited much greater yields (about 30% for all the complexes) than when tert-butyl hydroperoxide was employed (about 17% of yield with complex 1). The alcohol/ketone ratio in the reactions with hydrogen peroxide after 24 h was around 1.5, indicating cyclohexanol selectivity, while with tert-butyl hydroperoxide the ratio was around 0.7–1.0. In conclusion, the studied complexes can be considered good catalysts to oxidize the cyclohexane in mild conditions.

A novel Ce/AlPO-5 catalyst for solvent-free liquid phase oxidation of cyclohexane by oxygen

Cerium-containing AlPO-5 with an AFI structure has been prepared by hydrothermal synthesis in the presence of HF, and characterized by XRD, XPS, SEM, N2 adsorption/desorption, solid state 27Al, 31P MAS NMR and TG-DTA techniques. The results show that all the samples have good crystallinity, high dispersity of Ce and high surface area, and Ce(III) replaces the position of Al(III) and enters the framework of AlPO-5. Ce/AlPO-5 is a very efficient catalyst for the oxidation of cyclohexane in a solvent-free system with oxygen as an oxidant. In the condition of 0.5 MPa O2 and 413 K for 4 h, the conversion of cyclohexane is 13%, the total selectivity of cyclohexanol and cyclohaxnone is above 92%. In addition, the Ce/AlPO-5 catalyst is very stable in the cyclohexane oxidation system.

Highly efficient catalysts of chitosan-Schiff base Co(II) and Pd(II) complexes for aerobic oxidation of cyclohexane in the absence of reductants and solvents

Three chitosan-Schiff base Co(II) and Pd(II) complexes were prepared in a simple way and characterized by FT-IR, XPS and TG. Their abilities to catalyze oxidation of cyclohexane into cyclohexanone and cyclohexanol with oxygen in the absence of any solvents or reducing agents were studied. It has been revealed that the complexes had high catalytic activities for heterogeneous cyclohexane oxidation with oxygen. Especially, the oxidation of cyclohexane catalyzed by chitosan-salicyaldehyde Schiff base Co(II) complex under 1.6 MPa of initial oxygen pressure at 418 K gave excellent results with 9100 turnover numbers (based on the cobalt atom) and 96% selectivity for cyclohexanone and cyclohexanol after reaction of 4.5 h. The influences of oxygen pressure, reaction temperature and reaction time on the oxidation of cyclohexane were also investigated. It has been also revealed that the complexes were efficient for the oxidation of bulky cyclic alkanes and linear alkanes.

Photon Flux and Wavelength Effects on the Selectivity and Product Yields of the Photocatalytic Air Oxidation of Neat Cyclohexane on TiO2 Particles

Product selectivity and yields of cyclohexanol and cyclohexanone formation in the photocatalytic air oxidation of cyclohexane on TiO(2) particles were determined as a function of the irradiation wavelength (254 < or = lambda/nm < or = 366) and the photon flux (0.3 < or = I(0)/neinstein cm(-2) s(-1) < or = 5.0). Photonic efficiencies for total monooxygenated products (cyclohexanol + cyclohexanone) ranged from 10 to 25% depending on photon energy and fluency. The cyclohexanol-to-cyclohexanone ratio linearly increases with the incident photon flux at each wavelength and varies more than a magnitude order -- from 3 to 32%-at the same incident photon fluency -- 5 neinstein cm(-2) s(-1) -- by changing the irradiation wavelength from 366 to 303 nm. Experimental evidence indicates that both spectral and intensity effects emerge as a consequence of the change in the frequency of photon absorption per particle. A mechanism is proposed which accounts for the origin of the selectivity changes.

Mesoporous VMCM-41: highly efficient and remarkable catalyst for selective oxidation of cyclohexane to cyclohexanol

Liquid phase oxidation of cyclohexane was carried out under milder reaction conditions over mesoporous VMCM-41 molecular sieve catalysts using aqueous hydrogen peroxide as oxidant, acetic acid as solvent, and methyl ethyl ketone as initiator. The catalysts showed high substrate conversion and excellent product (cyclohexanol) selectivity. Although the activity of the catalyst slightly decreased after first recycle, owing to leaching of small amount of non-framework vanadium ions, it, however, remained nearly same thereafter. This observation was further confirmed by washing experiments where the non-framework vanadium ions were removed upon ammonium acetate treatment. Further, the washed catalyst also showed an activity similar to that of the recycled catalyst. Thus, the recycled or washed VMCM-41 behaves truly as heterogeneous catalyst. This observation was complemented and confirmed by both filtrate and quenching studies. The effects of reaction time, temperature, Si/V molar ratio, and catalyst concentration on the catalyst performance were examined in order to optimize the conversion of cyclohexane and selectivity of cyclohexanol. However, the use of strong oxidizing agent, e.g., tertiary butyl hydroperoxide, resulted in the formation of cyclohexanone as the major product. In addition, the use of solvents like methanol, dioxan and acetone showed lower activity.

Catalysis of chitosan-supported iron tetraphenylporphyrin for aerobic oxidation of cyclohexane in absence of reductants and solvents

The chitosan-supported iron(III) tetraphenylporphyrin was prepared and characterized structurally, and its ability to catalyse oxidation of cyclohexane into cyclohexanone and cyclohexanol with air in absence of any reductants and solvents was studied. The research results showed that the amino groups of the chitosan coordinated axially with the iron atoms of chloro[tetraphenylporphinatoiron(III)] to form chitosan-supported ironporphyrin, which has better catalytic power for cyclohexane oxidation with air than the corresponding unsupported ironporphyrin. Under reaction conditions of 418 K and 0.8 MPa, the cyclohexane oxidation catalyzed by chitosan-supported iron(III) tetraphenylporphyrin had 1.40×10 5 catalyst mole turnover (based on the iron atom), 10.48% cyclohexane conversion and the 79.20% cyclohexanone and cyclohexanol selectivity, respectively. The turnover in cyclohexane oxidation catalyzed by the supported ironporphyrin is about 22 times bigger than that by unsupported ironporphyrin and the conversion is about double. The values are also higher than 3.9% conversion and 78% selectivity catalyzed by soluble cobalt catalyst used in industry at present. This paper has also investigated the influences of reaction time, temperature and pressure on the catalyst turnover, cyclohexane conversion and ratio of cyclohexanol to cyclohexanone in the cyclohexane oxidation catalyzed by the chitosan-supported iron(III) tetraphenylporphyrin.