Liquid-phase Oxidation Of Benzene Research Articles

Thermal catalysis vs. photocatalysis: A case study with FeVO4/g-C3N4 nanocomposites for the efficient activation of aromatic and benzylic C[sbnd]H bonds to oxygenated products

Three semiconductor metal vanadates FeVO4, BiVO4, and LaVO4 were synthesized. To improve the thermal catalytic and photocatalytic activity of highly efficient metal vanadate FeVO4, nanocomposites of FeVO4 and graphitic C3N4 were prepared. Nanocomposites were prepared via thermal annealing method by varying the composition of FeVO4 and g-C3N4. Catalysts were characterized by a series of complementary combination of powder X-ray diffraction, thermogravimetric analysis, N2 adsorption-desorption, scanning/transmission electron microscopy, energy dispersive X-ray analysis, Fourier transform infrared spectroscopy, diffuse reflectance ultraviolet-visible spectroscopy, X-ray photoelectron spectroscopy, photoluminescence, and photoelectrochemical techniques. Catalysts were investigated in the liquid phase oxidation of benzene, phenol, hydroquinone, naphthalene, anthracene, toluene, ethyl benzene, di-phenyl methane, and p-xylene under conventional thermal condition and visible light irradiation condition. Kinetic and thermodynamic parameters (such as k, Ea, ΔH, ΔG, and ΔS) were calculated for the benzene hydroxylation by varying the reaction parameters under thermal catalytic condition. In order to confirm the active species responsible for the thermal catalytic and photocatalytic processes, UV–vis, fluorescence, cyclic voltammetry, and radical scavenging experiments were carried out with the help of suitable probe molecules. Based on the results obtained, reaction mechanism was proposed, and the structure-activity relationship was established. The catalyst was magnetically separated and recycled with negligible loss in the activity which is important for the sustainable heterogeneous catalysis. The developed catalytic process has the potential for the sustainable synthesis of a wide range of industrially important fine chemicals. Such a unique and detailed investigation of comparative study between thermal catalysis and photocatalysis using FeVO4/g-C3N4 nanocomposite will be highly useful to design optimum catalyst for an appointed catalytic reaction.

Preparation of iron oxide nanocatalysts and application in the liquid phase oxidation of benzene

Abstract A series of iron oxide nanocatalysts were prepared using an ultrasonically assisted co-precipitation technique. Molybdenum promoted Fe3O4 and Fe2O3 were prepared from the original materials by wet impregnation using a solution of ammonium molybdate. The catalysts were tested in the liquid phase oxidation of benzene at atmospheric pressure and at 60°C using molecular oxygen. Phenol yields between 7% and 14.5% were obtained. The major products were pyrogallol and catechol.

Surfactant-assisted Hydrothermal Synthesis of Ceria-Zirconia Nanostructured Materials for Catalytic Applications

CeO2-ZrO2 oxides were prepared by the surfactant-templated method using cetyl trimethyl ammonium bromide (CTAB) as template and modified with chromium nitrate. These were characterized by XRD, FT-IR, TEM, SEM, BET and TPD-CO2. The XRD data showed that as prepared CeO2-ZrO2 powder particles have single phase cubic fluorite structure. HRTEM shows mesoscopic ordering. Average particle size is 12-13 nm as calculated from particle histogram. The nitrogen adsorption/desorption isotherm were classified to be type IV isotherm, typical of mesoporous material. The presence of uni-modal mesopores are confirmed by the pore size distribution which shows pore distribution at around 60 A°. Catalytic activity was studied towards liquid-phase oxidation of benzene. Keywords- Mixed rare earth oxide, Ceria-zirconia, BET, TEM, benzene oxidation.

Liquid-phase oxidation of benzene to phenol using CuO catalytic polymeric membranes

Catalytic polymeric membranes filled with copper oxides of different particles size were prepared and tested in the liquid phase oxidation of benzene to phenol. Polyvinylidenefluoride (PVDF) was used as polymer to make the membranes. Three different solvents, dimethylacetammide (DMAc), dimethylformammide (DMF) and 1-methyl-2-pyrrolidone (NMP) were used as polymer solvents and distilled water as a nonsolvent. The prepared membranes were characterised morphologically by scanning electron microscopy (SEM). Pore size distribution was determined using gas a permeation method. Membrane characterisation tests evidenced that DMAc was the best solvent. Permeability tests were carried out for measuring the contact time of the catalyst with the reacting mixture. Catalytic membranes were tested in the liquid phase oxidation reaction of benzene to phenol by using hydrogen peroxide as oxidant in an ultrafiltration membrane reactor. The obtained results showed a higher phenol concentration using the PVDF membrane filled with the CuO nanopowder rather than CuO powder catalysts. A phenol concentration of 2.4 g L −1 and a benzene conversion to phenol of 2.3% were obtained using a contact time with the catalyst of 19.4 s at 35°C.

Liquid-Phase Oxidation of Benzene to Phenol by Molecular Oxygen over La Catalysts Supported on HZSM-5

The liquid-phase oxidation of benzene to phenol over lanthanum oxide catalysts (LaOx/HZSM-5) supported on HZSM-5 was studied in the presences of oxygen as an oxidant and ascorbic acid as a reducing regent. LaOx/HZSM-5 effectively catalyzes the formation of phenol at 353 K under the pressurization of oxygen. The LaOx/HZSM-5 catalysts take place no leaching of lanthanum species from the catalysts to acidic solvent. Therefore, it is demonstrated that the supported lanthanum catalysts are stable and reusable for the benzene oxidation even in the acidic reaction solution.

Structural and catalytic investigation of vanadia supported on ceria promoted with high surface area rice husk silica

Rice husk silica was utilized as the promoter of ceria for preparing supported vanadia catalysts. Effect of vanadium content was investigated with 2–10 wt.% V 2O 5 loading over the support. Structural characterization of the catalysts was done by various techniques like energy dispersive X-ray (EDX), X-ray diffraction (XRD), BET surface area, thermal analysis (TGA/DTA), FT-infrared spectroscopy (FT-IR), UV–vis diffused reflectance spectroscopy (DR UV–vis), electron paramagnetic spectroscopy (EPR) and solid state magnetic resonance spectroscopies ( 29Si and 51V MASNMR). Catalytic activity was studied towards liquid-phase oxidation of benzene. Surface area of ceria enhanced upon rice husk silica promotion, thus makes dispersion of the active sites of vanadia easier. Highly dispersed vanadia was found for low V 2O 5 loading and formation of cerium orthovanadate (CeVO 4) occurs as the loading increases. Spectroscopic investigation clearly confirms the formation of CeVO 4 phase at higher loadings of V 2O 5. The oxidation activity increases with vanadia loading up to 8 wt.% V 2O 5, and further increase reduces the conversion rate. Selective formation of phenol can be attributed to the presence of highly dispersed active sites of vanadia over the support.

Partial Oxidation of Benzene in Benzene-Water Bi-Phase System

The liquid-phase oxidation of benzene to phenol in a benzene-water bi-phase system was studied. The catalyst was dissolved in water that was saturated with benzene. Therefore benzene was oxidized to phenol in water. The produced phenol was extracted to the benzene phase. By extracting the produced phenol into the organic phase, products were easily separated from the catalyst. Therefore consecutive oxidation of phenol was prevented. The experiment was carried out in a stirred tank batch reactor. Two kinds of catalyst systems were used. One was an Fe-H 2 O 2 system and the other was a V-O 2 system. The effect of the reaction conditions such as hydrochloric acid concentration, oxidant concentration and catalyst concentration on the yield of phenol and selectivity to phenol in the Fe-H 2 O 2 system was discussed. The yield became large at low hydrochloric acid concentrations, high oxidant concentrations and high catalyst concentrations. The selectivity was independent of the oxidant concentration and the catalyst concentration. But the hydrochloric acid concentration affected the selectivity. The effect of the catalyst concentration on the yield of phenol and the selectivity to phenol in the V-O 2 system was discussed. The yield was increased with an increase of catalyst concentration. Selectivity slightly decreased when the yield increased. An extractor that had aqueous alkaline, was used to separate phenol from the reactor. Selectivity was improved when phenol was taken out from the reactor by the extractor in both catalyst systems cases.

Liquid-Phase Oxidation of Benzene to Phenol over V-Substituted Heteropolyacid Catalysts

The liquid-phase oxidation of benzene was carried out in aqueous acetic acid solvent over V-substituted heteropolyacids (V−HPAs) using molecular O2 and ascorbic acid as the oxidant and reducing reagent, respectively. Phenol was exclusively obtained as the oxygenation product. The elimination of the V species from the V−HPA (Keggin structure) catalyst into the reaction solvent during the benzene oxidation reaction was largely inhibited by ion-exchanging the proton of the V−HPA catalyst with Cs+. The main active species were assumed to be the V species anchored in the HPA. The influences of the reaction temperature, the concentration of acetic acid in the aqueous solvent, and the reaction pressure on the yield of phenol were investigated to obtain the optimal reactions condition for phenol formation. The reuse of the V−HPA catalyst caused gradual deactivation for phenol formation, despite the retention of the structure of the V−HPA catalyst. The deactivation was suggested to be due to the reduction of the V species in the V−HPA catalyst on the basis of the diffuse reflection spectra of the used catalysts.

Hydrogen peroxide oxidation of aromatic hydrocarbons by immobilized iron(III)

Abstract Supported iron(III) ions on neutral γ-alumina are an efficient catalyst for the oxidation of aromatic hydrocarbons with hydrogen peroxide in acetonitrile at 60 °C. The catalyst is active in the low temperatue liquid phase oxidation of benzene, toluene, chlorobenzene, p-xylene, mesitylene, benzaldehyde with hydrogen peroxide. Conversions of 31–88% with respect to starting substrate were obtained within 6 h. Oxidation on both the side chain and the aromatic ring of hydrocarbons occurred.

BiO x clusters occluded in a ZSM-5 matrix: preparation, characterization, and catalytic behavior in liquid-phase oxidation of hydrocarbons

A series of Bi-ZSM-5 containing 4.26, 5.54, and 6.64 wt% bismuth oxide was prepared by introducing Bi during ZSM-5 synthesis. For comparison, 5 wt% Bi (expressed as bismuth oxide)-impregnated ZSM-5 samples were also prepared. These samples were characterized by N 2 adsorption–desorption isotherms at 77 K, XRD, XPS, IR spectroscopy in the lattice vibration range and in the presence of chemisorbed pyridine and CO 2 and EXAFS. The characterization data confirmed the occlusion of bismuth oxide clusters in the zeolite pores. An intrinsic acidity due to bismuth oxide clusters was evidenced. This consisted, on one hand, in weak Lewis acid sites, ascribed to coordinatively unsaturated bismuth cations, and, on the other hand, in strong Brönsted acid sites, attributed to boundary Bi⋯OSi linkages. These catalysts were tested in the liquid-phase oxidation of benzene, toluene, and cyclohexane using hydrogen peroxide as oxidizing agent. The results showed that Bi-ZSM-5 catalysts are more active than the reported titanium silicalites, but the efficiency of H 2O 2 use was quite small, an important part of this being nonselectively decomposed. A good selectivity was observed in cyclohexane oxidation.

Biphasic oxidation of arenes with oxygen catalysed by Pd(II)—heteropoly acid system: oxidative coupling versus hydroxylation

Liquid-phase oxidation of benzene or toluene with oxygen (100–140 °C, 5–10 atm, in AcOH–H 2O) catalysed by the Pd(OAc) 2–H 5[PMo 10V 2O 40] redox system leads mainly to oxidative coupling (biphenyl and terphenyl or bitolyl) and ring hydroxylation (phenol or cresol). The reaction has been carried out homogeneously (at [H 2O] <15 vol.% in the solvent) and in biphasic conditions including an arene phase and an AcOH–H 2O catalyst phase (at [H 2O] >15 vol.%). The biphasic oxidation using AcOH–H 2O 80:20 (v/v) as the solvent has been found to be more efficient towards the oxidative coupling than the homogeneous system (AcOH–H 2O 95:5 (v/v)) in terms of both catalytic activity and selectivity to biaryls. Increasing the H 2O/AcOH ratio in the solvent (up to AcOH–H 2O 30:70 (v/v)) greatly enhances the ring hydroxylation to form phenol with 64% selectivity at 6% benzene conversion (100 °C, 5 atm O 2, 2 h).

Oxidation of hydrocarbons with peroxides catalyzed by chromium(III) and iron(III) incorporated in SAPO-37 framework

SAPO-37 containing structural chromium(III) and iron(III) ions were tested as catalysts in liquid phase oxidation of benzene and cyclohexane, using hydrogen peroxide and tert-butylhydroperoxide as oxidants. Only chromium(III) is active as oxidation catalyst. In spite of the SAPO-37 framework stability under the reaction conditions, leaching of small quantities of chromium occurs and the observed catalytic reaction is mainly due to the chromium ions in solution.

Incorporation of Iron(III) and Chromium(III) in SAPO-37

Incorporation of iron(III) and chromium(III) in the SAPO-37 framework was investigated. Pure faujasite structures were obtained using a molar composition of 0.95 Al 2O 3 : 1.0 P 2O 5 : 0.50 SiO 2 : 0.05 Me : 1.0 (TPA) 2O : 0.05 (TMA) 2O : 120 H 2O (Me = Fe or Cr) in the synthesis gel and a crystallization temperature of 180°C. Iron replaces tetrahedrally coordinated aluminum in the structure, whereas chromium is preferentially coordinated to the oxygen atoms of the lattice, probably in structural defects, and only a minor amount is in an isomorphous position. A major part of the tetrapropylammonium ions, located in the supercages, can be exchanged by sodium ions in methanolic solution without a significant loss of crystallinity of the samples. FeAPSO-37 and CrAPSO-37 are active catalysts in the liquid-phase oxidation of benzene and cyclohexane.

Phenol synthesis by liquid-phase oxidation of benzene with molecular oxygen over iron-heteropoly acid

The phenol synthesis by liquid-phase oxidation of benzene with molecular oxygen over iron-heteropoly acid (HPA) system was studied. When iron salts were used with H 3PW 12O 40, the highest activity was obtained. Spectroscopic studies showed that the state of the iron ion was changed after interaction with heteropoly acid (HPA) while the Keggin structure of HPA remained. The acidic nature of HPA activated benzene to form cationic species. Insoluble iron ion-exchanged heteropoly acid was obtained by partial ion exchange method, which also showed high activity on oxidation of benzene with molecular oxygen. The effects of reaction conditions were studied and the mechanism of deactivation was discussed. For the regeneration of catalytic activity, the addition of l-ascorbic acid as a reducing agent was suggested.

Liquid-Phase Benzene Oxidation to Phenol with Molecular-Oxygen Catalyzed by Cu-Zeolites

The oxidation of benzene to form phenol using cuprous chloride as a catalyst has been reported by Sasaki and his co-workers, who used reaction system oxygen molecules as the oxidant. Takehira and his co-workers have studied benzene oxidation with molecular oxygen catalyzed by Cu(II) salts in the presence of ascorbic acid. Cu ion-exchanged zeolites have been reported to be useful as catalysts for the gas-phase oxidation of some organic materials, and copper ions in zeolites have been indicated to have redox properties according to physicochemical measurements. Armed with this knowledge, the authors have tried the liquid-phase oxidation of benzene with molecular oxygen under atmospheric pressure at room temperature using Cu ion-exchanged zeolite catalysts in the presence of ascorbic acid as a reducing reagent for Cu ions. The catalytic behavior of the Cu zeolites for the benzene oxidation was compared with that of nonanchored cupric and cuprous chloride catalysts. Also, some Cu catalysts impregnated on some amorphous oxide supports, in addition to the zeolites, were tested as catalysts for benzene oxidation with molecular oxygen. 13 refs., 5 figs., 3 tabs.

Liquid phase oxidation of benzene to phenol over K2Cr2O7/SiO2

Catalytic behavior of K2Cr2O7 supported on SiO2 has been tested in the liquid phase oxidation of benzene to phenol. A small amount of phenol is detected in the presence of air. The yield of phenol is almost 100 times larger than on air oxidation when H2O2aq is used as an oxidant.