液相氧化环己烷制备环己酮的鼓泡塔新工艺

在连续无搅拌鼓泡塔反应器中,以环烷酸钴为催化剂,研究了空气液相氧化环己烷制备环己酮的氧化过程. 考察了空气流速、环己烷停留时间、催化剂浓度、压力及温度对反应效果的影响. 结果表明,在无搅拌鼓泡塔中,采用空气氧化环己烷制备环己酮的适宜操作条件为：反应温度413~423 K,压力1.2~1.5 MPa;当空气表观气速为2.5~3.5 cm/s、环己烷停留时间为30~40 min时,反应转化率为5%~7%,选择性达到80%~85%.     

Partial oxidation kinetics of m-hydroxybenzyl alcohol with noble metal catalysts in supercritical carbon dioxide

Partial oxidation of m-hydroxybenzyl alcohol was studied over several supported noble metal catalysts in a temperature range from 373 to 413 K, up to 2 MPa of oxygen pressure and 20 MPa of carbon dioxide pressure. The major product detected was m-hydroxybenzaldehyde. A charcoal supported palladium catalyst gave the highest yield of the aldehyde. For high temperature above 393 K and high oxygen pressure above 0.5 MPa, total oxidation was observed, which caused the selectivity of m-hydroxybenzaldehyde to decrease. Supercritical carbon dioxide medium seemed to improve heat dissipation of the reaction to allow the partial oxidation of m-hydroxybenzyl alcohol to occur under mild conditions. The partial oxidation of benzyl alcohol over a charcoal supported palladium catalyst was also examined for comparison and the major product formed was benzaldehyde. The conversion of benzyl alcohol and the selectivity to benzaldehyde was higher than those for the case of partial oxidation of m-hydroxybenzyl alcohol.     

Oxidation of styrene over polymer‐ and nonpolymer‐anchored Cu(II) and Mn(II) complex catalysts

Catalytic oxidation of styrene was investigated over polymer‐ and nonpolymer‐anchored Cu(II) and Mn(II) complex catalysts prepared by schiff base tridentate ligands. The effect of temperature, styrene to H₂O₂ mole ratio and catalyst amount on the catalytic activity and product selectivity was investigated. Further, the catalysts were characterized by various techniques, such as elemental analysis, atomic absorption spectroscopy (AAS), FTIR, FE‐SEM, EDAX, TGA, and UV–vis spectrophotometer. The elemental analysis, EDAX and AAS results confirmed the formation of Cu(II) and Mn(II) complexes, and it was found that the metal loading in the polymer‐anchored complex catalysts were in the range of 0.53–3.74 %. FTIR results showed the co‐ordination bond formation between the polymer ligands and metal ion. The catalytic data showed that, over all the catalysts, the main reaction products were benzaldehyde, styrene oxide, and benzoic acid. The polymer‐anchored complex catalysts were found to be much more active when compared with nonpolymer‐anchored catalysts. The maximum conversion of styrene (92.3%) was obtained over PS‐[Cu(Hfsal‐aepy)Cl] catalyst with benzaldehyde selectivity to 69% at the styrene to H₂O₂ mole ratio of 1 : 4 at 75°C. Although the PS‐[Mn(Hfsal‐aepy)Cl] catalyst was less active, it was highly selective to benzaldehyde. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Photocatalytic oxidation of cyclohexane over TiO2 nanoparticles by molecular oxygen under mild conditions

The structure, physical characteristics and photocatalytic selective oxidation properties of nanometer‐size TiO₂ particles produced by a sol–gel method were studied by X‐ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), X‐ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) and photocatalytic selective oxidation measurements. Analysis of the XRD results shows that sol–gel‐produced TiO₂ nanoparticles have the anatase structure at annealing temperatures ≤973 K, that the rutile structure begins to emerge at annealing temperatures ≥973 K and the particles have the pure rutile structure at 1023 K. DRS indicates that the obtained TiO₂ nanoparticles exhibit a blue shift with decreasing crystallite size. Analysis of the XPS results shows that the TiO₂ nanoparticles have a lot of oxygen vacancies. The EPR spectrum of TiO₂ at 77 K is composed of a strong isotropic EPR Surface‐Ti³⁺ signal(I) at g = 1.926 and a weak broad Bulk‐Ti³⁺ signal (II) at g = 1.987. Quantitative EPR indicates that both signals show a size and temperature dependence. Photocatalytic oxidation of cyclohexane into cyclohexanol with high selectivity and activity has been obtained by activation of molecular oxygen over sol–gel‐produced TiO₂ nanoparticles under mild conditions in dry solvent, which reveals that the quantum size effect and surface state effect of nanoparticles are key points for governing the selective photocatalytic reaction. The photocatalytic oxidation mechanism under dry solvent is different from that in aqueous solutions. Copyright © 2003 Society of Chemical Industry     

Effect of oxygen functional groups on synthetic carbons on liquid phase oxidation of cyclohexanone

Synthetic carbons from phenolic resins were used as catalysts for the aqueous phase oxidation of cyclohexanone to C₄-C₆ dicarboxylic acids (adipic, glutaric and succinic acids) at 413 K under 50 bar total air pressure. The changes in microporous structure and surface chemistry, produced as a consequence of activation or heat treatment processes, were analyzed. Using CO₂ or air as activating agent increased significantly the surface area and the total pore volume responsible for the activity. The surface chemistry of the samples was also modified and was characterized by titration with bases of different strength and with HCl, by temperature programmed desorption, and by X-ray photoelectron spectroscopy. To determine the role of surface oxygen functionalities on the catalytic behavior of the carbons, heat treatments in nitrogen at different temperatures were used to selectively eliminate oxygenated groups. Thus, treatment at temperatures of 1173 K eliminating the carbonyl/quinone groups decreased the selectivity to adipic acid and dicarboxylic acids. Introducing quinone groups during the synthesis of the carbons also improved the selectivity to adipic acid, proving that the mechanism of oxidation involves the quinone type groups on the carbon surface.     

颗粒内部毛细凝聚对气体有效扩散系数的影响

采用改进型Wicke-Kallenbath稳态扩散池,在373～413 K及0.4～1.0 MPa条件下测定了氢气在某工业催化剂CuO/ZnO/γ-Al₂O₃内部的有效扩散系数。实验采用逐步增加环己烷流量至某最大值而后逐步降低回到初始点的方法,测定了催化剂孔内发生毛细凝聚时氢气有效扩散系数随环己烷蒸气相对压力的变化。实验结果表明:在 373 K下环己烷蒸气相对压力为0.42时开始发生毛细凝聚,而在413 K下则延迟到0.6才开始出现这一现象。此外,滞后环宽度随着温度的升高而变窄,并且氢气的有效扩散系数随环己烷蒸气相对压力变化出现多重滞后环。建立了催化剂部分润湿时氢气的有效扩散系数与内部润湿分率的关联式,与实验测量值符合较好。     

Reprint of: Oxidative dehydrogenation of cyclohexane and cyclohexene over supported gold, –palladium catalysts

Supported gold, palladium and gold–palladium catalysts have been used to oxidatively dehydrogenate cyclohexane and cyclohexenes to their aromatic counterpart. The supported metal nanoparticles decreased the activation temperature of the dehydrogenation reaction. We found that the order of reactivity was Pd ≥ Au–Pd > Au supported on TiO₂. Attempts were made to lower the reaction temperature whilst retaining high selectivity. The space-time yield of benzene from cyclohexane at 473 K was determined to be 53.7 mol/kg_cat/h rising to 87.3 mol/kg_cat/h at 673 K for the Pd catalyst. Increasing the temperature in this case improved conversion at a detriment to the benzene selectivity. Oxidative dehydrogenation of cyclohexene over AuPd/TiO₂ or Pd/TiO₂ catalysts was found to be very effective (conversion >99% at 423 K). These results indicate that the first step in the reaction sequence of cyclohexane to cyclohexene is the slowest step. These initial results suggest that in a fixed-bed reactor the oxidative dehydrogenation in the presence of oxygen, palladium and gold–palladium catalysts are readily able to surpass current literature examples and with further modification should yield even higher performance.     

Kinetics of Liquid‐Phase Hydrogenation of Iso‐valeraldehyde to Iso‐amyl Alcohol Over A Ru/Al2O3 Catalyst

The liquid‐phase catalytic hydrogenation of iso‐valeraldehyde to iso‐amyl alcohol was studied in a slurry reactor. The kinetics of liquid‐phase hydrogenation of iso‐valeraldehyde over a 5% Ru/Al₂O₃ catalyst was studied in the range of temperature 373‐393 K and H₂ pressure 0.68‐2.72 MPa using 2‐propanol as the solvent. The selectivity to iso‐amyl alcohol was 100%. The kinetic data were analyzed using a simple power law model. A single site Langmuir‐Hinshelwood type model suggesting dissociative adsorption of hydrogen and surface reaction as the rate‐controlling step provided the best fit of the experimental data. The catalyst could be reused thrice without any loss in activity.     

Supported dicopper(II) complex catalyst Cu2(II)(μ-Br)2/SiO2: synthesis, characterization and catalytic properties for synthesis of ethylene carbonate

A μ-Br-bridged dicopper(II) complex, namely [Cu₂(μ-Br)₂·6H₂O](ClO₄)₂, has been prepared by metal ion grafting. A supported complex catalyst Cu₂(II)(μ-Br)₂/SiO₂was prepared by modifying the silica surface with NaOEt and anchoring the dicopper(II) complex precursor on the surface of the support. The structure of the complex catalyst has been characterized by elemental analysis, IR spectra and UV–VIS diffusion reflection spectra. Obtained data were compared with published data of the complex. TPD-MS and TPD-IR investigations indicated that CO₂ and ethylene oxide (EO) can be chemisorbed on the surface of the catalyst reversibly in a bridged state and can be desorbed from the surface at 105 and 115 K, respectively. In the high temperature range of 450–573 K, another reversible absorption state for CO₂ was also discovered. For EO, however, a decomposition absorption state was found which gave the dissociated species of CH₄ and CO. TPSR-MS experiments have shown that CO₂ and EO reacted on the surface effectively in the range of 343–413 K. An in situ IR method has been used to study the reactivity of the reactants on the surface of the catalyst, and the target product ethylene carbonate (EC) was detected in the range of 333–413 K. Catalytic experiments indicated that the one-way yield of EC is greater than 8.0% and that the selectivity of EC is greater than 82%. A synergic cyclization reaction pathway is proposed to account for the observed products.     

Efficient room temperature oxidation of cyclohexane over highly active hetero-mixed WO3/V2O5 oxide catalyst

An efficient room temperature catalyzed oxidation of cyclohexane to cyclohexanone (K) and cyclohexanol (A) was achieved over hetero-mixed tungsten–vanadia (WO₃/V₂O₅) using H₂O₂ oxidant. WO₃/V₂O₅ exhibited high catalytic activity to initiate the free-radical oxyfunctionalization of cyclohexane to afford up to 90% conversions within 6 h. The KA selectivity was found to depend on reaction time and the amount of catalyst. The WO₃/V₂O₅ catalyst was highly recyclable with consistent catalytic activity.     

Hydrogenation of methyl propionate over Ru–Pt/AlOOH catalyst: Effect of surface hydroxyl groups on support and solvent

A ruthenium–platinum bimetallic catalyst supported on boehmite was prepared by co-impregnation and hydrothermal reduction and characterized by XRD, TEM and TG–DTG. Reduction time of the catalyst affected the conversion of γ-Al₂O₃ to boehmite and the specific surface area of the catalyst, and consequently influenced the catalytic performance of the catalyst. Under the same conditions, the Ru–Pt/AlOOH catalyst showed much higher activity and selectivity than the Ru–Pt/γ-Al₂O₃ in aqueous hydrogenation of methyl propionate. The selectivity to 1-propanol of 97.8% could be obtained at methyl propionate conversion of 89.1% over Ru–Pt/AlOOH at 453 K under 5 MPa of H₂ for 6 h. It is postulated that the high performance of this novel catalyst is related to the cooperation of the hydroxyl groups of support surface and water solvent.     

Liquid-Phase Oxidation of Cyclohexane over Co-TUD-1

Cobalt was successfully incorporated into TUD-1 and characterized by means of X-ray powder diffraction, UV–Vis spectroscopy, N₂ adsorption and elemental analysis. The catalyst is highly efficient in the oxidation of cyclohexane with TBHP under solvent-free and mild oxidation conditions.     

Immobilization of manganese tetraphenylporphyrin on Au/SiO2 as new catalyst for cyclohexane oxidation with air

Manganese tetraphenylporphyrin was successfully immobilized on Au/SiO₂, by using mercaptopyridine with sulfhydryl and pyridyl groups as bridging agent. The synthesized catalyst with novel structure was characterized by FTIR spectroscopic technique, XPS measurement, TG–DTA analysis and so on. During aerobic oxidation of cyclohexane in the presence of this material, the conversion of cyclohexane and total selectivity to cyclohexanone and cyclohexanol were up to 5.39% and 88.74%, respectively.     

Characterization and Activity of Cu/ZSM5 Catalysts for the Oxidation of Phenol with Hydrogen Peroxide

The heterogeneous catalytic wet peroxide oxidation (CWPO), involving total oxidation of organic compounds to CO₂ and H₂O is a possible path for the treatment of toxic and bio‐refractory wastewater streams. The aim of this work was to synthesize and characterize three Cu/ZSM5 catalysts prepared by direct hydrothermal synthesis. The mass ratio of the active metal component in the zeolite ranged from 1.62–3.24 wt %. These materials were tested for CWPO of aqueous phenol in a stainless steel Parr reactor, in batch operation under mild conditions (at atmospheric pressure and a temperature of 353 K). The catalyst weight was 0.1 g dm^–3 and the initial concentration of phenol and hydrogen peroxide were 0.01 mol dm^–3 and 0.1 mol dm^–3, respectively. The catalysts were characterized by powder X‐ray diffraction (XRD), scanning electron microscopy (SEM), AAS and ICP‐MS. Their catalytic performance was monitored in terms of phenol and total organic carbon (TOC) conversion, hydrogen peroxide decomposition, by‐product distribution and the degree of copper leached into the aqueous solution. The experimental results indicated that within 180 min, these catalysts facilitated almost complete elimination of phenol and a significant removal of chemical oxygen demand, without significant leaching of Cu ions from the zeolite. The Cu/ZSM5‐DHS3 catalyst with the highest copper loading was proven to be the best candidate. The useful fraction of hydrogen peroxide that contributed to the removal of the organic compounds quantified in terms of selectivity, S, indicated that the CWPO selectivity was always less than 100 %, which meant that there was some self‐degradation of oxidant. It was also shown that oxidation of phenol took place on the catalyst surface via a heterogeneous mechanism, and that the contribution of any homogeneous reaction mechanism was not significant.     

α-Zirconium phosphate supported metal–salen complex: synthesis,characterization and catalytic activity for cyclohexane oxidation

Metal–salen intercalated α-zirconium phosphate, abbreviated as {α-ZrP·M(Salen), where M = Fe(III) and Mn(II)} was synthesized insitu by the flexible ligand method. The structure of resulting compounds was characterized by BET surface area, powder X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray analysis, X-ray photoelectron spectroscopy, thermogravimetric analysis and UV–visible spectroscopy. The catalytic activity of α-ZrP·M(Salen) was tested for the oxidation of cyclohexane using dry tert-butylhydroperoxide as an oxidant. In the oxidation reaction, cyclohexane was oxidized to cyclohexanol (A), cyclohexanone (K) and some unidentified products. It was found that the reactivity of α-ZrP·Fe(Salen) is greater than α-ZrP·Mn(Salen) in the oxidation reaction. Influence of various reaction parameters viz. reaction temperature, catalyst concentration, substrate to oxidant molar ratio was studied using α-ZrP·Fe(Salen) catalyst to obtain maximum conversion (29.30%) of cyclohexane. The catalyst was reused for five cycles without significant loss of catalytic activity.     

Effect of Rh content on carbon-supported PtRh catalysts for dehydrogenative electrooxidation of cyclohexane to benzene over polymer electrolyte membrane fuel cell

Electrochemical dehydrogenative oxidation of cyclohexane to benzene was studied over carbon-supported PtRh (PtRh/C) electrocatalysts, which were prepared with different Pt:Rh atomic ratios from 4:1 to 1:4 using a borohydride reduction method combined with freeze-drying procedure at room temperature. The bimetallic PtRh/C catalysts were characterized by various physicochemical analyses such as X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray absorption-near-edge spectroscopy (XANES). The variation of Rh content over the PtRh alloy formation caused significant structural and electronic modifications on the catalyst phase, which could be associated with consistent changes in electrocatalytic activities over a polymer electrolyte membrane (PEM) fuel cell. The Pt₄Rh₁/C catalyst as the anode electrocatalyst showed a maximum power density of ca. 8.5 mW cm^?2. Here, both the structural modification via lattice parameter change and the electronic modification through charge transfer from Rh to Pt could kinetically facilitate the sluggish electrode reaction with an increased exchange current density on the dehydrogenative electrooxidation of cyclohexane to benzene over the PtRh/C anodes of cyclohexane fuel cell.     

Butene Catalytic Cracking to Propene and Ethene over Potassium Modified ZSM-5 Catalysts

Catalytic cracking of butene over potassium modified ZSM-5 catalysts was carried out in a fixed-bed microreactor. By increasing the K loading on the ZSM-5, butene conversion and ethene selectivity decreased almost linearly, while propene selectivity increased first, then passed through a maximum (about 50% selectivity) with the addition of ca. 0.7–1.0% K, and then decreased slowly with further increasing of the K loading. The reaction conditions were 620 °C, WHSV 3.5 h⁻¹, 0.1 MPa 1-butene partial pressure and 1 h of time on stream. Both by potassium modification of the ZSM-5 zeolite and by N₂ addition in the butene feed could enhance the selectivity towards propene effectively, but the catalyst stability did not show any improvement. On the other hand, addition of water to the butene feed could not only increase the butene conversion, but also improve the stability of the 0.7%K/ZSM-5 catalyst due to the effective removal of the coke formed, as demonstrated by the TPO spectra. XRD results indicated that the ZSM-5 structure of the 0.07% K/ZSM-5 catalyst was not destroyed even under this serious condition of adding water at 620 °C.     

Enhanced hydroformylation by carbon dioxide‐expanded media with soluble Rh complexes in nanofiltration membrane reactors

A novel process for continuous hydroformylation in CO₂‐expanded liquids (CXLs) is demonstrated using bulky phosphite ligands that are effectively retained in the stirred reactor by a nanofiltration membrane. The reactor is operated at 50°C with a syngas pressure of 0.6 MPa to avoid CO inhibition of reaction rate and selectivity. The nanofiltration pressure is provided by ～3.2 MPa CO₂ that expands the hydroformylation mixture and increases the H₂/CO ratio in the CXL phase resulting in enhanced turnover frequency (～340 h^?1), aldehydes selectivity (>90%) and high regioselectivity (n/i ～8) at nearly steady operation. The use of pressurized CO₂ also reduces the viscosity in the CXL phase, thereby improving the mass‐transfer properties. Constant permeate flux is maintained during the 50 h run with Rh leakage being less than 0.5 ppm. This technology concept has potential applications in homogeneous catalytic processes to improve resource utilization and catalyst containment for practical viability. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4287–4296, 2013     

碳纳米管负载纳米二氧化钌一步催化氧化环己烷

以不同载体负载的纳米二氧化钌作为催化剂，O₂为氧化剂，实现一步催化氧化环己烷制备己二酸，考察催化剂载体、引发剂、反应时间、温度和压力对环己烷转化率和己二酸选择性的影响。结果表明，碳纳米管负载纳米二氧化钌作为催化剂具有高的活性和选择性；在125 ℃、1.5 MPa和反应6 h的条件下，环己烷转化率达到40％，己二酸选择性达80％以上；催化剂可重复使用，具有较好的稳定性。     

Redox kinetics of benzene oxidation to maleic anhydride

Steady state kinetics of the oxidation reaction have been determined with the help of a gradientless semi-differential, fixed-bed reactor. The Mars and van Krevelen phenomenological model satisfactorily correlates the experimental data but a modification of the Langmuir-Hinshelwood model taking into account partial coverage of the catalyst surface with reaction intermediates is preferred. Transient kinetics have been studied with a new automated periodic-pulse reactor, directly connected to a gas chromatograph. The response of a catalyst (essentially V₂O₅–MoO₃) to reduction and oxidation has been investigated. The rate of bulk (lattice) oxygen utilization as well as the degree of carbon coverage are estimated by this technique. Selectivity is dependent on the oxidation state of the catalyst: high partial pressure of either benzene or oxyen and high temperatures are detrimental to selectivity.