Cyclohexanol Research Articles

Catalytic activity of cobalt and cerium catalysts supported on calcium hydroxyapatite in ethanol steam reforming

Abstract In this paper, Co,Ce/Ca10(PO4)6(OH)2 catalysts with various cobalt loadings for steam reforming of ethanol (SRE) were prepared by microwave-assisted hydrothermal and sol-gel methods, and characterized by XRD, TEM, TPR-H2, N2 adsorption-desorption measurements and cyclohexanol (CHOL) decomposition tests. High ethanol conversion (close to 100%) was obtained for the catalysts prepared by both methods but these ones prepared under hydrothermal conditions (HAp-H) ensured higher hydrogen yield (3.49 mol H2/mol C2H5OH) as well as higher amount of hydrogen formed (up to 70%) under reaction conditions. The superior performance of 5Co,10Ce/HAp-H catalyst is thought to be due to a combination of factors, including increased reducibility and oxygen mobility, higher density of basic sites on its surface, and improved textural properties. The results also show a significant effect of cobalt loading on catalysts efficiency in hydrogen production: the higher H2 yield exhibit catalysts with lower cobalt content, regardless of the used synthesis method.

Effect of hydroxypropyl-β-cyclodextrin and coadjuvants on the sorption capacity of hydrophilic polymer films for monoterpene alcohols

Chitosan films filled with hydroxypropyl-β-cyclodextrin at a 1:1 weight ratio and plasticized with 35 or 50% glycerol or 35% propylene glycol were prepared by casting and conditioned at different relative humidities to achieve a similar water content. Sorption properties of the films for various monoterpene compounds with phenolic, or with linear or cyclohexyl alcohol structures were studied after their immersion in the volatile liquids. In general, the films presented a considerable capacity to retain monophenolic compounds, with sorption values ranging from 455% for meta-cumenol to 193% for guaiacol, for chitosan films with the same formulation. These values were two orders of magnitude higher than those of compounds without the phenol group. The affinity for monophenolic compounds decreased in films plasticized with hydrophilic propylene glycol, whereas no changes were observed in the retention of non-phenolic monoterpenes. Replacement of chitosan with polyvinyl alcohol polymer considerably decreased the retention of monophenolic compounds, with the exception of isoeugenol. Finally, the antimicrobial activity of monoterpenes and films loaded with them was evaluated in vitro by the microatmosphere test against Escherichia coli and Staphylococcus aureus. The present study shows that hydroxypropyl-β-cyclodextrin and the plasticization level achieved by hydrophilic films can be used to regulate loading capacity and sorption selectivity of naturally occurring antimicrobial compounds.

Commercial catalysts screening for liquid phase nitrobenzene hydrogenation

In this work, a series of commercially available materials was screened for the catalytic hydrogenation of nitrobenzene (NB). The materials revealed different performances, particularly different activities in what concerns the NB conversion, and notably diverse selectivities towards the industrially desired reaction product, aniline (ANL). The catalysts’ active phases are based on Pd and Ni (respectively groups I and II), namely 1wt.% Pd/Al2O3 (catalyst I.1), 0.3wt.% Pd/Al2O3 (catalyst I.2), 0.3wt.% Pd/Al2O3 (catalyst I.3), and 50wt.% NiO/(Al2O3+SiO2) (catalyst II.1). The fresh and used materials were characterized by several physical-chemical techniques, specifically scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), nitrogen adsorption (with BET surface area determination), X-ray diffraction (XRD), H2 temperature-programmed reduction (TPR), inductively coupled plasma mass spectrometry (ICP-MS) and elemental (CHNS) analysis. It was shown that the catalysts are stable in the conditions studied and no deactivation was found. The characterization results allowed explaining the catalytic behavior of the tested materials. In particular, catalyst I.1 was found to be the less active, probably due to its much lower BET surface area (and larger Pd particle size). On the other hand, catalyst I.2 was the more active, which was well correlated to the smaller average particle size (along with narrower Pd particle size distribution) and smaller pellet size, although the active metal content is low. Finally, it was observed that catalyst II.1 is the most selective towards light by-products (benzene (Bz), cyclohexylamine (CHA), cyclohexanol (CHOL) and cyclohexanone (CHONA)), probably due to its lower pore size dimensions.

Oxidovanadium(IV) complexes with tridentate N-heterocycle ligands: Synthesis, structure, and efficient catalyst for cyclohexane oxidation to cyclohexanone

A series of coordination oxidovanadium(IV) complexes: [VOSO4 (bpz-eaT)]·C4H6O4 (1), [VOSO4(bpz-eaT)]·0.5(C10H18O4) (2) and [VOSO4 (bpz-eaT)]·C5H8O4·CH3CN (3) (bpz-eaT=2,4-bis (3,5-dimethyl-1H-pyrazol-1-yl)-6-diethylamino-1,3,5-triazine) were synthesized in MeCN. All of the complexes are characterized by elemental analysis, IR spectra and single-crystal X-ray diffraction. The single-crystal X-ray diffraction analyses reveal that the vanadium atoms are six-coordinated in all complexes. In the study of Cyclohexane (Cy) oxidation, promoted by our complexes, the effects of the amount of H2O2 and HNO3 were investigated. It was found that complex 3 exhibited the highest catalytic activity in MeCN at 9h, 60°C, which is the first oxidovanadium(IV) complex catalyst that we found can catalyze Cy produce more cyclohexanone (CyO) than cyclohexanol (CyOH) oxidated by H2O2.

Solvothermal synthesis and characterization of mixed oxides with perovskite-like structure

Solvothermal synthesis was successfully used to prepare LaMeO3 (Me=Mn, Co, Fe) and La1−xSrxMnO3 (x=0.1, 0.3, 0.5), mixed oxides with perovskite-like structure. The prepared materials were examined by X-ray diffraction (XRD), nitrogen adsorption at low temperature (BET), transmission electron microscopy (TEM), decomposition of cyclohexanol (CHOL), temperature programmed reduction with hydrogen (TPRH2), temperature programmed desorption of oxygen (TPDO2) and X-ray photoelectron spectroscopy (XPS). Furthermore, catalytic activity for combustion of 0.6% vol. methane in air (GHSV=40000h−1) was determined.All prepared materials are nanocrystalline and well-crystallized, and they exhibit relatively well-developed specific surface area (9.2–39.2m2/g). The trigonal structure of the Mn-containing samples corresponds to the structure of the high-temperature bulk phase, which cannot be recovered at ambient conditions. Generally, the Mn-containing materials exhibit higher SSA, more basic character of the surface, lower temperature of maximum H2 consumption and higher catalytic activity in lean methane combustion than the corresponding Co- and Fe-based nanocrystals. The highest catalytic activity for lean methane combustion (100% of CH4 conversion at 451°C) is observed for LaMnO3. A partial substitution of La by Sr lowers content of Mn4+ on the surface of the corresponding materials, resulting in lower catalytic activity in lean methane combustion.

Lactic Acid Promoted Cyclohexane Oxidation with Ammonium Paramolybdate

Cyclohexane oxidation is one of the most important industrial reactions. In order to find more efficient and cheap catalysts for this reaction,we studied the catalytic activity of ammonium paramolybdate( APM). By GC analysis,we focus on the effects of the species and the amount of the acids on the reactivity.Compared with nitric acid,lactic acid is more effective for the oxidation of cyclohexanol to cyclohexanone,and thus improve the TON( turn over number) value of the target products from 124 to 161. Furthermore,we propose a possible reaction mechanism of this new way for green oxidation of cyclohexane.

Rapid determination of products of phenol hydrogenation in a supercritical water system using headspace gas chromatography

AbstractThis paper reports a headspace analysis technique for the determination of products, i.e., cyclohexanone (CE) and cyclohexanol (CL), of phenol hydrogenation in a supercritical water reaction system (SWRS) with water removal by hydrate formation. An addition of anhydrous calcium chloride leads to water absorption resulting in crystal water; thus, the samples can be quantitatively measured without the influence of water. After achieving equilibrium at 150­°C and maintaining it for 5 min, the obtained results showed a relative standard deviation of less than 5.3 % and the recovery ranged from 93 % to 104 %. The presented method is simple and accurate for the analysis of CL, CE and phenol in samples from phenol conversion in SWRS.

Densities, viscosities, sound speed, and IR studies of N-methyl-2-pyrrolidone with cyclohexylamine, cyclohexanol, and cyclohexene at different temperatures

Abstact Densities, viscosities, and speeds of sound of the binary liquid mixtures of N-methyl-2-pyrrolidone (NMP) with cyclohexylamine (CHA), cyclohexanol (CHOL) and cyclohexene (CHE) at temperatures of 303.15–318.15 K are measured over the entire composition range. From the experimental values excess molar volume V m E , deviation in isentropic compressibility Δks, excess free length L f E , deviation in viscosity Δη are computed. The variation with the temperature and concentration is discussed in terms of molecular interactions. All the excess parameters and deviations are fitted to Redlich–Kister polynomial equation to estimate the binary interaction parameters and mean deviation from the regression lines. The sign and magnitude of the computed parameters are discussed to reveal the nature and type of interactions existing between the component molecules in the binary mixtures. Thermodynamic investigations under the present study reveal the strong inter molecular interactions between the unlike molecules in the binary systems of NMP + CHA, NMP + CHOL, whereas in the other binary system NMP + CHE the reverse trend is observed due to dispersion forces. The strength of interaction of CHA, CHOL, and CHE with NMP found to follow the order: CHA > CHOL > CHE. FT-IR studies of these mixtures have been estimated and analyzed to study the interactions between unlike molecules. A good agreement is observed between the excess parameters and FT-IR studies.

Solid phase microextraction method for characterizing the organic fraction of an industrial brine stream

The manufacturing process of DOW Chemical Company in Portugal produces a brine stream containing organic contaminants. For recovering the sodium chloride by-product, it is necessary to fully characterize this brine stream. With this purpose, a direct immersion-solid phase microextraction-gas chromatograph (SPME-GC) analytical method was successfully optimized and implemented, being possible to quantify accurately, with reproducibility, the organic fraction at ppb levels. The effects of salt content, extraction time, temperature, and pH were investigated, and the SPME experimental conditions optimized. For the poly(dimethylsyloxane-co-divinylbenzene) fiber utilized, the resulting parameters were: 25% (wt.) of NaCl, 30 min, 20°C, and pH 11. The fiber desorption was performed at 250°C for 15 min. The calibration curves of the representative organics of the brine (benzenamine, cyclohexanamine, 2-methylbenzenamine, N–cyclohexylcyclohexanamine, cyclohexyl alcohol, nitrobenzene, cyclohexanone, and 4-phenylcyclohexylamine) presented good correlation coefficients (0.991 ⩽ R2 ⩽ 0.997). The detection limits of the method were determined for each species for the optimized analytical conditions; the detection limits vary from 0.21 to 3.22 ppb, respectively for N–cyclohexylcyclohexanamine and benzenamine, the, precision ranged from 4.4 to 8.7% RSD and the validation criteria was obeyed for all analytes. The industrial brine stream was then characterized during several days to register the concentration history of contaminants. Independently of the stream composition fluctuations, the SPME methodology developed and optimized in this work was able to assess accurately their concentrations at ppb levels.

Simultaneous phase and morphology controllable synthesis of copper selenide films by microwave-assisted nonaqueous approach

Copper selenide films with different phase and morphology were synthesized on copper substrate through controlling reaction solvent by microwave-assisted nonaqueous approach. The films were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The result showed that the pure films could be obtained using cyclohexyl alcohol or benzyl alcohol as solvent. The cubic Cu2−xSe dendrites were synthesized in cyclohexyl alcohol reaction system and hexagonal CuSe flaky crystals were obtained with benzyl alcohol as solvent.

Utilization of cyclohexanol dehydrogenation in a novel thermally coupled reactor for Fischer–Tropsch synthesis in gas to liquid technology

In this study, the dehydrogenation of cyclohexanol (CLL) and its utilization in a novel thermally coupled reactor for Fischer–Tropsch synthesis (FTS) has been investigated. In the new configuration, the produced heat of FTS reactions is removed by the endothermic reaction of CLL dehydrogenation instead of circulating high-pressure boiling water in the conventional reactor (CR). The products of this reaction are hydrogen and cyclohexanone (CLN). Some of the generated hydrogen is utilized in synthesis gas and also in hydro cracking unit for production of GTL products and other is stored and used in some other processes. Gasoline(C5+) – the desirable product – alongside some undesirable products like carbon dioxide and methane are produced in FTS reactions. To demonstrate the superiority and advantages of this new configuration it has been compared with another thermally coupled reactor for FTS in which the dehydrogenation of cyclohexane works as coolant reaction in the endothermic side of the reactor. In order to analyze this novel reactor a one-dimensional heterogeneous model has been applied. After modeling and solving the differential equations, the excellence and advantages of new configuration are clarified. The (C5+) yield is increased and a reduction in the generation of undesirable products like CO2 and CH4 is observed in this new configuration. Moreover, hydrogen and CLN which both are useful products are generated in considerable amounts in the endothermic side of the reactor.

Visible light-induced partial oxidation of cyclohexane on WO3 loaded with Ptnanoparticles

Photocatalytic oxidation of cyclohexane (CHA) with molecular oxygen (O2) was carried out using WO3 loaded with Pt nanoparticles (Pt/WO3) under irradiation of visible light (λ > 420 nm). The Pt/WO3 catalysts promote oxidation of CHA and give rise to partial oxidation products such as cyclohexanol (CHA-ol) and cyclohexanone (CHA-one) with ca. 93% selectivity. Among the catalysts, Pt/WO3 with 0.2 wt% Pt shows the highest activity. The high selectivity for partial oxidation on Pt/WO3 is because subsequent photocatalytic decomposition of partial oxidation products is suppressed. In the Pt/WO3 system, the photoformed electrons on the conduction band of WO3 are consumed by a multi-electron reduction of O2 on the Pt particles (formation of H2O and H2O2), where a single-electron reduction of O2 is unfavored. This suppresses the formation of a superoxide anion (O2˙−) that promotes decomposition of CHA-ol and CHA-one and, hence, results in selective formation of partial oxidation products.

Theoritical Evaluation of Ultrasonic Velocities in Binary Liquid Mixtures ofN-Methyl-2-pyrrolidone at Different Temperatures with Some Cyclic Compounds

Ultrasonic velocities and densities of the binary liquid mixtures ofN-methyl-2-Pyrrolidone (NMP) with Cyclohexylamine (CHA), Cyclohexanol (CHOL) and Cyclohexene(CHE) at a temperature range of 303.15 to 318.15 K over the entire composition range were measured. The theoretical values of ultrasonic velocity were evaluated using the Nomoto's relation(UNR), Impedence relation(UIR), Ideal mixing relation(UIMR), Jungie's relation(UJR) and Rao's specific velocity relation(UR).The molecular interaction parameter (α) was computed by using the experimental and theoretical ultrasonic velocity values. The variation of interaction parameter with the composition of the mixture has been discussed in terms of molecular interactions.

Synthesis of highly reactive polyisobutylenes with BF3·cyclohexanol initiating system

The selective cationic polymerization of isobutylene (IB) initiated by a BF3·cyclohexanol (CL) complex was carried out from the mixed C4 fraction feed containing the 4C saturated and unsaturated hydrocarbons at −20°C. The effects of CL concentration, BF3 concentration, solvent for preparing BF3·CL complex and polymerization time on the chemical structure of end groups, number-average molecular weight (M n) and molecular weight distribution (MWD, M w/M n) of the resulting polymers were investigated. The experimental results indicate that the BF3·CL complex initiating system exhibited an extremely high selectivity toward the cationic polymerization of IB in the mixed C4 fraction feed and low molecular weight (M n = 900–3600) polyisobutylenes (PIBs) with large proportion of exo-double bond end groups were obtained. The exo-double bond content in PIB chain ends increased by increasing CL concentration or by decreasing solvent polarity in initiating system, BF3 concentration and polymerization time. The M n and MWD of the resulting PIBs were dependent on the concentrations of CL and BF3. Highly reactive PIBs with around 90 mol% of exo-double bonds were successfully synthesized by the selective polymerization of IB from the mixed C4 fraction feed, providing a potentially practical process for its simplicity and low costs.

Structure-reactivity relationship for alcohol oxidations via hydride transfer to a carbocationic oxidizing agent

Second-order rate constants were determined for the oxidation of 27 alcohols (R1R2CHOH) by a carbocationic oxidizing agent, 9-phenylxanthylium ion, in acetontrile at 60 °C. Alcohols include open-chain alkyl, cycloalkyl, and unsaturated alcohols. Kinetic isotope effects for the reaction of 1-phenylethanol were determined at three H/D positions of the alcohol (KIEα-D = 3.9, KIEβ-D3 = 1.03, KIEOD = 1.10). These KIE results are consistent with those we previously reported for the 2-propanol reaction, suggesting that these reactions follow a hydride-proton sequential transfer mechanism that involves a rate-limiting formation of the α-hydroxy carbocation intermediate. Structure–reactivity relationship for alcohol oxidations was deeply discussed on the basis of the observed structural effects on the formation of the carbocationic transition state (Cδ+OH). Efficiencies of alcohol oxidations are largely dependent upon the alcohol structures. Steric hindrance effect and ring strain relief effect win over the electronic effect in determining the rates of the oxidations of open-chain alkyl and cycloalkyl alcohols. Unhindered secondary alkyl alcohols would be selectively oxidized in the presence of primary and hindered secondary alkyl alcohols. Strained C7C11 cycloalkyl alcohols react faster than cyclohexyl alcohol, whereas the strained C5 and C12 alcohols react slower. Aromatic alcohols would be efficiently and selectively oxidized in the presence of aliphatic alcohols of comparable steric requirements. This structure–reactivity relationship for alcohol oxidations via hydride-transfer mechanism is hoped to provide a useful guidance for the selective oxidation of certain alcohol functional groups in organic synthesis. Copyright © 2011 John Wiley & Sons, Ltd.

Sr 1− xK xTiO 3 catalysts for diesel soot combustion

Strontium titanates partially substituted with potassium (Sr 1− x K x TiO 3, x = 0.1–0.5) were prepared by sol–gel citric method. The obtained materials were characterized by XRD, S BET and cyclohexanol (CHOL) decomposition measurements, their catalytic activity in soot combustion was determined. It has been shown that substitution of strontium by potassium lowers temperature of soot ignition temperature by 270 °C in a 10% O 2 in Ar atmosphere and ca 400 °C in a 1500 ppm of NO 2, 10% O 2 in Ar atmosphere for Sr 0.2K 0.2TiO 3. The potassium promoting effect is discussed in terms of surface basicity and creation of oxygen vacancies where molecular oxygen or (NO, NO 2) is adsorbed forming basic surface oxygen species active for soot oxidation.

Production of hydrogen through the coupling of dehydrogenation and hydrogenation for the synthesis of cyclohexanone and furfuryl alcohol over different promoters supported on Cu–MgO catalysts

Cu–MgO is found to be an efficient catalyst for the coupling reaction of furfural (FAL) hydrogenation and cyclohexanol (CyOH) dehydrogenation. This process is not only efficient in compensating the thermodynamic equilibrium constraints in the cyclohexanol dehydrogenation and improving the yields towards cyclohexanone but also is a economical route for the synthesis of furfuryl alcohol (FFA) and cyclohexanone (Cyone) as the process do not need any external pumping of hydrogen. The effect of incorporation of various promoters viz., Co, Zn, Fe, Cr, Pd and Ni in Cu–MgO over its activity towards this coupling reaction has been studied. Incorporation of Cr in Cu–MgO catalyst is found be an advantageous in enhancing the yields of both FFA and Cyone. All other promoters though found to show higher activity for the individual reactions of FAL hydrogenation and CyOH dehydrogenation, failed to do the same in their coupling reaction. The stabilization of active species (Cu +/Cu 0) by Cr which also seem to increase the synergetic interaction between Cu and MgO as observed from higher dispersion of copper (from XRD results) and easier reducibility of copper oxide (from TPR results) seem to be the factors behind its higher activity over other promoted catalysts.

Synthesis of Boric Acid Ester Catalyzed by Pyrrolidonium Acidic Ionic Liquid

Esterification reaction of boric acid,pinacol and cyclohexanol has been studied in ionic liquids(IL),including 1-methyl-2-pyrrolidonium hydrogen sulfate([Hnmp]HSO4),1-butyl-3-methylimidazolium tetrafluoroborate([Bmim]BF4) and 1-butyl-3-methylimidazolium hexafluorophosphate([Bmim]PF6).The influences of the types of ionic liquids,reaction temperature,reaction time and molar ratio of reactants to IL on the yields of 2-cyclohexyloxy-4,4,5,5-tetramethyl-[1,3,2]dioxaborolan have been investigated.The results showed that under the optimized conditions[n(boric acid):n(pinacol):n(cyclohexanol):n([Hnmp]HSO4) = 1:1:1:1,70 ℃ and 4 h],the yield of 2-cyclohexyloxy-4,4,5,5-tetramethyl-[1,3,2] dioxaborolan could reach up to 72.5%.The ionic liquid can be used repeatedly for four times without remarkable loss of the catalytic activity.

Hydrophobic Cr–Si mixed oxides as a catalyst for visible light-induced partial oxidation of cyclohexane

Photocatalytic oxidation of cyclohexane (CHA) with molecular oxygen has been performed with hydrophobic Cr–Si mixed oxides as a catalyst under visible light irradiation (λ > 400 nm). The Cr–Si catalysts with highly dispersed chromate species were prepared by hydrolysis of tetraethyl orthosilicate (TEOS), organoalkoxysilane (1,2-bis(triethoxysilyl)ethane: BTESE), and Cr(NO3)3 followed by calcination. All of the Cr–Si catalysts promote partial oxidation of CHA to cyclohexanol (CHA-ol) and cyclohexanone (CHA-one) with high selectivity (>99%). Among the Cr–Si catalysts prepared with different TEOS and BTESE compositions, the catalyst prepared with 10% BTESE demonstrates the highest catalytic activity. The CHA vapor adsorption and electron spin resonance analysis reveal that the enhanced catalytic activity is due to the increased hydrophobicity of the catalyst surface, which enhances the access of CHA to the excited state chromate species.

Binuclear CuII complexes as catalysts for hydrocarbon and catechol oxidation reactions with hydrogen peroxide and molecular oxygen

The tridentate ligands HL1, [(2-hydroxybenzyl)(2-(imidazol-2-yl)ethyl)]amine, and HL2, [(2-hydroxybenzyl)(2-(pyridil-2-yl)ethyl]amine, were used to synthesize binuclear CuII complexes, [Cu2(L1)2]Cl2•2H2O, complex 1, and [Cu2(L2)2](ClO4)2•1.5H2O, complex 2, in order to obtain catalysts for oxidative processes. Both complexes were characterized by elemental analysis, IR, UV-Vis and EPR spectroscopies. In addition, they were studied by cyclic voltammetry and potentiometric titration in order to investigate their behavior in solution. The crystal structure of complex 1 revealed a binuclear cation where the metal centers are bridged by two phenoxo groups. This arrangement provides a Cu...Cu distance of 3.043(10) Å, which is similar to the observed for catechol oxidase (2.90 Å). The catalytic reactivities of both complexes were investigated for hydrocarbon and catechol oxidations. Complexes 1 and 2 led to low overall hydrocarbon oxidation conversion values of 6.34 % and 7.15 %, respectively. However, for complex 1, only cyclohexanol (Cy-OH) and cyclohexanone (Cy=O) were isolated as reaction products, with selectivities of 68.1% for Cy-OH. This low overall conversion is tentatively attributed to steric hindrance effects produced by the non-coplanar aromatic rings of the ligand scaffolds, which suggest that the access of the hydrocarbon molecule to the binuclear active center is a determinant step in the reaction mechanism. Investigation of catecholase activities has shown high efficiencies, with complex 2 being more active than complex 1. It indicates that the pyridine-containing ligand is able to stabilize the intermediate CuI CuI center which is proposed to be formed in this process. This is corroborated by the strong participation of pyridine in the LUMO (lowest unoccupied molecular orbital) of complex 2, which can help to accommodate the additional negative charge when the complex is reduced from CuII CuII to CuI CuI.