Cyclohexanone Selectivity Research Articles

Polarized Catalytic Polymer Nanofibers.

Molecular scale modifications were achieved by spontaneous polarization which is favored in enhancements of β-crystallization phase inside polyvinylidene fluoride (PVDF) nanofibers (NFs). These improvements were much more effective in nano and submicron fibers compared to fibers with relatively larger diameters. Metallic nanoparticles (NPs) supported by nanofibrous membranes opened new vistas in filtration, catalysis, and serving as most reliable resources in numerous other industrial applications. In this research, hydrogenation of phenol was studied as a model to test the effectiveness of polarized PVDF nanofiber support embedded with agglomerated palladium (Pd) metallic nanoparticle diameters ranging from 5–50 nm supported on polymeric PVDF NFs with ~200 nm in cross-sectional diameters. Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM), Energy Dispersive X-Ray Spectroscopy (EDX), Fourier Transform Infrared Spectroscopy (FTIR) and other analytical analysis revealed both molecular and surface morphological changes associated with polarization treatment. The results showed that the fibers mats heated to their curie temperature (150 °C) increased the catalytic activity and decreased the selectivity by yielding substantial amounts of undesired product (cyclohexanol) alongside with the desired product (cyclohexanone). Over 95% phenol conversion with excellent cyclohexanone selectivity was obtained less than nine hours of reaction using the polarized PVDF nanofibers as catalytic support structures.

Ionic liquids modified cobalt/ZSM-5 as a highly efficient catalyst for enhancing the selectivity towards KA oil in the aerobic oxidation of cyclohexane

AbstractThe industrial oxidation of cyclohexane is currently performed with very low conversion level, i.e. 4-6% conversion and poor selectivity for cyclohexanone and cyclohexanol (K-A oil), i.e.70-85%, at above 150oC reaction temperature and above 10atm reaction pressure using molecular oxygen oxidant and homogeneous catalyst. Several disadvantages are, however, associated with the process, such as, complex catalyst-product separation, high power input, and low safe operation. Therefore, the oxidation of cyclohexane using heterogeneous catalyst oxygen oxidant from air at mild conditions has received particular attention. Aerobic oxidation of cyclohexane over ionic liquids modified cobalt/ZSM-5 (IL-Co/ZSM-5) in absence of solvents was developed in this article. The prepared catalysts were characterized by XRD, FT-IR, N2 adsorption-desorption, SEM, TEM and XPS analyses. The influence of reaction parameters on the oxidation of cyclohexane was researched, such as the various catalysts, reaction temperature, reaction time, and the reaction pressure, on the process. Highly selective synthesis of KA oil was performed by aerobic oxidation of cyclohexane using ionic liquids modified cobalt/ZSM-5 (IL-Co/ZSM-5) as the catalyst in absence of solvents for the first time. A selectivity of up to 93.6% of KA oil with 9.2% conversion of cyclohexane was produced at 150℃ and 1.5 MPa after 3 h, with about 0.1 mol cyclohexane, C7mimHSO4-Co/ZSM-5 catalyst equal to 6.0 wt%, respectively. The induction period of oxidation was greatly shortened when the ionic liquid was supported on ZSM-5. The catalyst was easy to centrifuge and was reused after five cycles. It was found that both the characterization and performance of the catalysts revealed that both the presence of oxygen vacancies with incorporation of Co ions into the framework of ZSM-5 and the introduction of C7mimHSO4 into the ZSM-5 leads to the both satisfactory selectivity and robust stability of the C7mimHSO4-Co/ZSM-5 heterogeneous catalyst.

Hydrogenation of Phenol to Cyclohexanone over Bifunctional Pd/C-Heteropoly Acid Catalyst in the Liquid Phase

Cyclohexanone is an important intermediate in the manufacture of polyamides in chemical industry, but direct selective hydrogenation of phenol to cyclohexanone under mild conditions is a challenge. Hydrogenation of phenol to cyclohexanone has been investigated in the presence of the composite catalytic system of Pd/C-heteropoly acid. 100% conversion of phenol and 93.6% selectivity of cyclohexanone were achieved within 3 h under 80 °C and 1.0 MPa hydrogen pressure. It has been found that a synergetic effect of Pd/C and heteropoly acid enhanced the catalytic performance of the composite catalytic system which suppressed the hydrogenation of cyclohexanone to cyclohexanol.

Liquid Phase Selective Hydrogenation of Phenol to Cyclohexanone over Electrospun Pd/PVDF-HFP Catalyst

Cyclohexanone is an important industrial intermediate in the synthesis of materials such as nylons, but preparing it efficiently through one-step hydrogenation of phenol is hindered by over-reduction to cyclohexanol. Using an efficient catalyst can enhance the selectivity of cyclohexanone at high phenol conversion. In this study, catalysts comprised of palladium nanoparticles supported on electrospun PVDF-HFP (polyvinylidene fluoride-co-hexafluoropropylene) nanofibers were prepared using the electrospinning technique. The catalysts were characterized using thermogravimetric analyzer (TGA), scanning electron microscopy (SEM), transmission electron microscope (TEM), and drop shape analyzer (DSA). The prepared catalysts were used to hydrogenate phenol into cyclohexanone in a batch reactor. The Pd/PVDF-HFP catalyst showed a very high product selectivity and high phenol conversion. The conversion of phenol achieved was 98% with 97% cyclohexanone selectivity in 7 h using 15 wt% of palladium (0.0021 moles) relative to phenol (0.0159 moles). The turnover number (TON) and turnover frequency (TOF) values calculated were 7.38 and 1.05 h−1, respectively. This paper presents original research in heterogeneous catalysis using novel electrospun nanofibers. Multiphase hydrogenation of phenol to cyclohexanone over electrospun Pd/PVDF-HFP catalyst has not been reported by any researcher in the literature. This work will also provide a research window for the application of electrospun polymeric nanofibers in multiphase reactions.

Matching Relationship Between Carbon Material and Pd Precursor

The matching relationship between carbon material and Pd precursor was investigated by constructing Pd@C catalysts with four carbon materials (mesoporous carbon, activated carbon, N-doped carbon and O-doped carbon) and three Pd precursors (PdCl2, Pd(C2H3O2)2 and Pd(NO3)2) and evaluating their catalytic performance in the phenol hydrogenation to cyclohexanone. The Pd precursor or the carbon material has no obvious influence on the cyclohexanone selectivity, but strongly affects the catalytic activity. The Pd@C prepared via PdCl2 shows good performance among all tested catalysts due to higher Pd content and better Pd dispersion. Conversely, although Pd(NO3)2 is easily adsorbed by carbon carriers, the catalytic activity is poor due to the worse Pd dispersion. The Pd(C2H3O2)2 adsorption is very sensitive to the surface properties of carbon, and the N-doping can enhance the binding force between carbon and Pd2+, leading to higher Pd content and better Pd dispersion, thereby enhanced catalytic activity. This work would provide valuable references for the selection of Pd precursor for a given support.

Enhanced phenol hydrogenation for cyclohexanone production by membrane dispersion

Continuous liquid-phase phenol hydrogenation to cyclohexanone over Pd/Al2O3 was conducted in a membrane dispersion based fixed-bed reactor system. The effects of membrane structure on the phenol hydrogenation and gas–liquid two-phase flow were investigated by experimental results coupled with computational studies. The phenol conversion and cyclohexanone yield can be effectively improved by selecting suitable pore size and channel number of membrane. Gas holdup, axial fluid velocity and gas distribution predicted by computational fluid dynamics (CFD) studies provide insights into the relationship between membrane structure and catalytic efficiency. As compared to the phenol conversion and cyclohexanone yield obtained by direct feeding of hydrogen, those are enhanced substantially in the presence of membrane dispersion at the conditions of high LHSV and low hydrogen/phenol aqueous solution volume ratio. A phenol conversion above 85.6% and a cyclohexanone selectivity at ∼98% can be achieved in a continuous phenol hydrogenation to cyclohexanone of 50 h. This work will provide guidance for the green cyclohexanone production.

Fabrication of Pd@N-doped porous carbon-TiO2 as a highly efficient catalyst for the selective hydrogenation of phenol to cyclohexanone in water

A highly efficient catalyst with the structure of semiconductor–metal heterojunction for phenol hydrogenation in water was fabricated by loading the Pd nanoparticles on the N-doped porous carbon-TiO2 (CN-TiO2) materials, which was synthesized via the one-step carbonization of TiO2-contained ZIF-67. The microstructures of the as-prepared Pd@CN-TiO2 catalysts were investigated in detail and the catalytic properties were tested by the phenol hydrogenation under mild conditions. With increasing TiO2 amount, the charge transfer and specific surface area of Pd@CN-TiO2 initially increase and then reduce, thereby the catalytic performance show a similar regular pattern. The as-fabricated Pd@CN-TiO2 exhibits a superior catalytic performance than the Pd nanoparticles supported on TiO2 or CN separately, owing to their synergistic effect. When the parameters affecting the catalytic efficiency are optimized, the conversion of phenol and selectivity for cyclohexanone can even achieve 98% in pairs with a higher reaction rate of 0.45 mmol h−1. Furthermore, the Pd@CN-TiO2 shows stable performance in the recycling experiments.

Nitrogen doped graphene-supported trimetallic CuNiRu nanoparticles catalyst for catalytic dehydrogenation of cyclohexanol to cyclohexanone

In different hydrocarbons reactions, copper based catalysts have industrial importance especially in the synthesis of the cyclohexanone from dehydrogenation of the cyclohexanol. At operating conditions, one of the significant problems in the industrial process is fast deactivation of the copper based catalysts. The present work focuses on the formulation of two types of the supported catalysts namely supported tri metals alloy (CuNiRu/N-rGO) in paper forms and supported copper (Cu/N-rGO), analysing the properties of the synthesised catalyst support (N-rGO) by Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), Temperature-programmed desorption (TPD-NH3), Temperature Programmed Reduction (TPR-H2) and X-ray diffraction (XRD) as well as to investigate the catalytic performance of the two supported catalysts in the dehydrogenation of cyclohexanol to the cyclohexanone. All experiments on the catalytic performance were conducted at moderate temperatures (200–270 °C), 1 atm, 0.1 ml/min cyclohexanol flow rate and ∼8 h time on stream (TOS). The performances of the catalysts were evaluated in the gas phase dehydrogenation of cyclohexanol to the cyclohexanone. The conversion of the cyclohexanol using CuNiRu/N-rGO is 4% higher compare to use of the Cu/N-rGO. The selectivity for cyclohexanone in case of the Cu/N-rGO catalyst is about 83.88%, whilst, the CuNiRu/N-rGO illustrated approximately 6% better performance. The yield of the cyclohexanone using the Cu/N-rGO is about 78%, while by adding the Ni and Ru as promoters with the improvement of the Cu/N-rGO the yield of cyclohexanone was improved by 8%. The duration of the steady state period significantly improved by using CuNiRu/N-rGO which was proposed up to 7 times. This research shows that the CuNiRu/N-rGO catalyst provides the suitable and selective active sites for the dehydrogenation of cyclohexanol to the cyclohexanone reaction.

Selective hydrogenation of phenol to cyclohexanone by SiO2-supported rhodium nanoparticles under mild conditions

A silica-supported rhodium catalyst for the selective hydrogenation of phenol to cyclohexanone under mild conditions has been developed. As the Rh concentration on the catalyst increased from 0.5 to 15 wt%, the conversion (at phenol/Rh mole ratio 100/1) dropped whereas the initial selectivity to cyclohexanone increased. The direct hydrogenation to cyclohexanol occurred in parallel with partial hydrogenation to cyclohexanone. The negative correlation between selectivity and Rh dispersion suggests that direct hydrogenation occurs at low coordination sites whereas dissociation of phenol to phenoxy followed by hydrogenation to cyclohexanone takes place at higher coordinated terrace sites. DFT calculations revealed that the activation barrier for O–H bond cleavage is lower for phenol adsorbed on a Rh(1 1 1) flat surface than on small particles. By blocking the low coordination edge and step sites through grafting with (3-mercaptopropyl)trimethoxysilane, the cyclohexanone selectivity was improved from 82 to 93% at 100% conversion. The catalyst is active at room temperature and 1 atm H2 pressure and can be easily activated by in-situ reduction.

Immobilization of phosphotungstic acid on amine-grafted graphene oxide via a facile and efficient solid-phase reaction for the selective oxidation of cyclohexanol

Phosphotungstic acid was immobilized on the surface of 3-aminopropyltrimethoxysilane -grafted graphene oxide by one-step solid phase reaction between acid and base. The synthesized catalyst was characterized by Fourier transform infra-ed spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy, thermogravimetry, elemental analysis, NMR and contact angle measurements. The catalyst was exploited for selective oxidation of cyclohexanol to cyclohexanone. The catalytic results indicated that the cyclohexanol conversion of 89.2% along with cyclohexanone selectivity of 95.4% was achieved in selective oxidation of cyclohexanol using H2O2 as oxidant over the as-prepared catalyst. It also could be easily recovered and reused for at least four times without any significant loss in activity.

Synthesis of CuCr2O4/Reduced Graphene Oxide Composite: A Green Catalyst for Selective Oxidation of Cyclohexane to Cyclohexanone with Hydrogen Peroxide

AbstractCuCr2O4/reduced graphene oxide (rGO) composites were prepared using a two‐step method. Detailed characterizations of the material were performed with X‐ray diffraction (XRD), Zeta potential, Fourier transform infrared (FT‐IR), transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS), Raman spectra, and Thermal Gravimetric Analyzer (TGA). The characterizations showed that the ∼50 nm CuCr2O4 nanoparticles were successfully supported on the rGO via static electricity. The TGA results showed that the quality of rGO in composites was around 10%. The experimental results showed that the catalysts obtained high catalytic activity for the selective oxidation of cyclohexane to cyclohexanone with H2O2. The catalyst obtained a conversion rate of cyclohexane of up to 95.8%. 78.1% cyclohexanone selectivity was obtained. The catalyst had good cycling stability after 5 reuses. Compared to the other composite materials, the catalyst had high catalytic activity for the selective oxidation of cyclohexane to cyclohexanone.

Enhanced Selectivity of Phenol Hydrogenation in Low-Pressure CO2 over Supported Pd Catalysts

Selective hydrogenation of phenol to cyclohexanone is an important process in both chemical industry and renewable feedstock processing. However, direct hydrogenation of phenol to cyclohexanone under mild conditions over catalysts with high reactivity, selectivity, and facile preparation is still a challenge. In the present study, we report that 99% conversion and 99% selectivity can be achieved over as-prepared Pd/γ-Al2O3 catalyst under the medium of low-pressure CO2 (0.05–0.2 MPa) and H2O at 373 K. According to experiment results, ab initio calculations and in situ high-pressure FTIR measurements indicated enhanced selectivity of cyclohexanone in low-pressure CO2; this result originated from the molecular interaction between cyclohexanone and CO2 and can prevent the further hydrogenation of cyclohexanone. Notably, enhancement of selectivity to cyclohexanone in low-pressure CO2 was also achieved using commercial Pd/γ-Al2O3 and Pd/C catalysts.

Tuning the selectivity of phenol hydrogenation on Pd/C with acid and basic media

The selectivity of phenol hydrogenation over Pd/C was successfully tuned by various Bronsted acid and base additives. Compared with neutral reaction condition, the basic condition witnessed decreased catalytic activity and cyclohexanone selectivity while the opposite trend was observed under acidic condition. Mechanistic studies indicated the varied interaction of substrate with acid and base is responsible for the activity difference, while the changed keto-enol tautomerization correlates directly to the selectivity variation.

A Side-Stream Catalysis/Membrane Filtration System for the Continuous Liquid-Phase Hydrogenation of Phenol over Pd@CN to Produce Cyclohexanone

A catalysis/membrane filtration system combining a catalytic reaction and a separation process can realize the in situ separation of ultrafine catalysts from the reaction mixture and make the production continuous. In this study, a side-stream catalysis/membrane filtration system was developed for the first time for the continuous liquid-phase hydrogenation of phenol over Pd@CN to produce cyclohexanone. The operating parameters including the reaction and filtration conditions were optimized by balancing their influences on the catalytic and separation properties. It was found that the properties of the side-stream catalysis/membrane filtration system depended strongly on the operating conditions. Continuous phenol hydrogenation over Pd@CN was performed under the optimized operating conditions. A stable operation of 30 h was achieved with both a phenol conversion and a cyclohexanone selectivity of greater than 85%, and the ceramic membrane showed excellent stability. This study is a contribution to the dev...

Comparison of Pd-UiO-66 and Pd-UiO-66-NH2 catalysts performance for phenol hydrogenation in aqueous medium

UiO-66, a kind of Metal-organic framework materials (MOFs) was used as a support for nano-palladium particles (i.e., Pd-UiO-66) which was used in the catalytic hydrogenation of phenol in aqueous media in this work. The performance of Pd-UiO-66 was compared with Pd-UiO-66-NH2, in which the UiO-66 support had been modified through the introduction of NH2 groups. Pd-UiO-66 and Pd-UiO-66-NH2 were characterized by BET, XRD, XPS and TEM. The results indicated that the Pd particles are embedded in Pd-UiO-66 and fixed on Pd-UiO-66-NH2. With NH2 groups, the crystalline structure of UiO-66-NH2 is somewhat damaged and the interaction between Zr and Pd in Pd-UiO-66-NH2 is rather weaker than in Pd-UiO-66. Pd-UiO-66 has high activity for aqueous phenol hydrogenation, with 100% conversion of phenol being achieved within 2h at 120°C, which is much higher than with the Pd-UiO-66-NH2 catalyst. Pd-UiO-66 has higher selectivity for cyclohexanol, and Pd-UiO-66-NH2 has higher selectivity for cyclohexanone under the same conditions. The study of the chemical kinetics portion revealed that the hydrogenation reaction rates with the Pd-UiO-66 catalyst are over 10 times higher than those with Pd-UiO-66-NH2 under the same conditions. The phenol hydrogenation catalyzed by Pd-UiO-66 is more sensitive to the reaction temperature than when catalyzed by the Pd-UiO-66-NH2 catalyst. Thus, it has been shown that modifications of an MOF support for a catalyst can result in structural changes that lead to different catalytic activities and selectivities in aqueous phenol hydrogenation.

Study on the formation of photoactive species in XPMo12-nVnO40- HCl system and its effect on photocatalysis oxidation of cyclohexane by dioxygens under visible light irradiation

The formation of photoactive species in the Keggin-type XPMo12-nVnO40 polyoxometalates (POMs, n=1-3, X=H+, tetramethyl (TMA). tetrabutyl (TBA) or cetyltrimethyl (CTMA) ammonium cation (Q+))-HCl system was researched in details by UV–vis and its photo-catalysis performance evaluated via the oxidation of cyclohexane by dioxygens (O2) in acetonitrile (MeCN) under visible light irradiation The results showed that the VV-O-M (M for VV or MoIV) sites of POM can capture HCl to form a protonated photoactive species (PA, POM-(VVOHM)+Cl−) and the solvent MeCN likely participates the formation of such PA species via weak coordination. This PA species, with a characteristic absorption band of 475nm, a 51V-NMR chemical shift of −550ppm and an oxidative potential of higher than 0.9V, should be responsible for the present photo-catalysis oxidation. The formation of PA species was accelerated significantly with increasing the V atoms incorporated into POMs, but hampered seriously in the presence of slight excess water due to the replaced effect of water for the coordinated HCl and MeCN. Notably, such impediment effect of water was weakened obviously over the Q+-containing POMs due to a hydrophobicity of these POM's. As a result, most of the Q+-containing POMs showed a higher activity for this photo-catalysis reaction in MeCN-HCl-H2O media than the H+-containing counterparts. Isotope tracing test of water-containing heavy oxygen 18O (97%) in photo-catalysis reaction indicated that the oxygen atoms in water had partly contribution to the formation of cyclohexanol (ca.8.2%) and especially cyclohexanone (ca. 33.3%), which can drastically restrain chlorinated side reactions and thus improve cyclohexanone selectivity. Based on these findings, a free-radical mechanism initiated by the Cl atoms generated in the excited POM-(VVOHM)+Cl− species was proposed.

Hydrogenation of Phenol over Pt/CNTs: The Effects of Pt Loading and Reaction Solvents

Carbon nanotubes (CNTs)-supported Pt nanoparticles were prepared with selective deposition of Pt nanoparticles inside and outside CNTs (Pt–in/CNTs and Pt–out/CNTs). The effects of Pt loading and reaction solvents on phenol hydrogenation were investigated. The Pt nanoparticles in Pt–in/CNTs versus Pt–out/CNTs are smaller and better dispersed. The catalytic activity and reuse stability toward phenol hydrogenation both improved markedly. The dichloromethane–water mixture as the reaction solvent, compared with either pure medium, decreased the catalytic activity toward phenol hydrogenation and selectivity of cyclohexanone over Pt–in/CNTs, but significantly improved the catalytic activity toward phenol hydrogenation and selectivity of cyclohexanone over Pt–out/CNTs.

Selective oxofunctionalization of cyclohexane over titanium dioxide–based and bismuth oxyhalide (BiOX, X = Cl−, Br−, I−) photocatalysts by visible light irradiation

Solar photocatalysis has been employed for pollutant removal by driving the substrates to complete mineralization. These unselective systems can become selective by tuning the reaction conditions and the properties of the photocatalyst for the oxofunctionalization of unreactive compounds such as hydrocarbons.This work focused on the selective oxofunctionalization of cyclohexane by visible light photocatalysis under ambient conditions. For this purpose, five titanium dioxide–based photocatalysts (Fe–doped TiO2, N–doped and undoped TiO2) and three bismuth oxyhalide photocatalysts (BiOCl, BiOBr and BiOI) were synthesized and characterized (XRD, DRS, SEM and BET surface area). The titanium dioxide–based photocatalysts showed the highest selectivity for cyclohexanone (cyclohexanone/cyclohexanol=4.49–87.50). BiOCl and BiOBr showed similar yields for cyclohexanone and cyclohexanol production (cyclohexanone/cyclohexanol=1.92 and 1.27, respectively). The BiOI photocatalysts showed the highest selectivity for cyclohexanol production (cyclohexanone/cyclohexanol=0.23). The cyclohexanol yield depended linearly on the bandgap of the BiOX. BiOI reached the maximum cyclohexanol yield (16.5±1.3μmolm−2g). In all assayed systems, the cyclohexyloxy radical was identified as an intermediate. However, only when BiOI was utilized was there evidence of OH radical production. A higher yield of cyclohexanol than cyclohexanone was obtained only by using this photocatalyst. Thus, the selectivity was associated with cyclohexanol production by hydroxylation of the cyclohexyl radical by the OH radical.

OXIDATION OF CYCLOHEXANOL ON PHOSPHOTUNGSTIC ACID ANION INTERCALATED LAYERED DOUBLE HYDROXIDES WITH AQUEOUS H2O2 AS OXIDANT

The layered double hydroxides (LDH) of Mg2AlNi and Mg3Al pillared by Keggin-type phosphotungstic acid anion (POM), i.e. Mg2AlNi-POM LDH and Mg3Al-POM LDH were synthesized by an ion-exchange method. The synthesized POM intercalated LDH compounds were characterized using various techniques such as FTIR, XRD, TGA and BET. The observed results show that the obtained catalysts retain the layer structure of LDH. Compared with the binary Mg3Al-POM LDH, the ternary Mg2AlNi-POM LDH catalyst indicated a higher thermal and chemical stability. The catalytic activity of the resulting LDH-POM was also assessed in the green oxidation of cyclohexanol with aqueous H2O2 as an oxidant. The Mg2AlNi-POM LDH showed a much higher conversion and selectivity for cyclohexanone than the corresponding Mg3Al-POM LDH catalyst.

Selective phenol hydrogenation to cyclohexanone over alkali–metal-promoted Pd/TiO2 in aqueous media

High conversion of phenol and high selectivity of cyclohexanone could be achieved by using alkali–metal-promoted Pd/TiO2 catalysts under mild conditions.