Effect of manganese on Cu/SiO2 catalysts for the dehydrogenation of cyclohexanol to cyclohexanone

The effect of the addition of manganese to Cu/SiO₂ catalysts for cyclohexanol dehydrogenation reaction was investigated. At reaction temperature of 250 °C, the conversion and the selectivity to cyclohexanone were both increased with the addition of manganese to Cu/SiO₂ catalyst. However, as the reaction temperature was further increased, higher loading of manganese in Cu/SiO₂ catalyst led to a decrease in the conversion of cyclohexanol. Manganese in Cu/ SiO₂ catalyst decreased the reduction temperature of copper oxide, increased the dispersion of copper metal, and decreased the selectivity to cyclohexene. It was found that the dehydration of cyclohexanol to cyclohexene occurred on the intermediate acid sites of catalyst. At high Mn loading, catalyst surface was more enriched with manganese in used catalyst compared to that in freshly calcined or reduced catalyst, which may account for the sharp decrease of the conversion at high temperature of 390 °C. Upon reduction, copper manganate on silica was decomposed into fine particles of copper metal and manganese oxide (Mn₃O₄).     

Silica-Supported Gold Catalyst Modified by Doping with Titania for Cyclohexane Oxidation

Amorphous silica was modified by doping with titania through a surface sol–gel process and applied as the support for depositing gold. These doped silica-supported gold catalysts were tested in the selective cyclohexane oxidation to cyclohexanone and cyclohexanol using oxygen. Under the oxidation conditions of 150 °C, 1.5 MPa and 3 h, a selectivity of 91.7% for cyclohexanone and cyclohexanol could be reached over the gold catalyst, affording a cyclohexane conversion of 8.4% and a turnover frequency up to 40,133 per hour. Moreover, the catalytic activity and selectivity could be well retained in 4 recycling oxidation reactions, showing a high stability of the gold catalyst supported on titania-doped silica.     

Preparation of MCM-41 Supported Salen Vanadium Complex and its Catalysis for the Oxidation of Cyclohexane with H<Subscript>2</Subscript>O<Subscript>2</Subscript> as an Oxidant

A secondary amino group modified MCM-41 (mobile crystalline material number 41) was synthesized and used as a support for the immobilization of a salen oxovanadium complex via a multi-grafting method. The immobilized complex was characterized by UV–Vis spectroscopy, X-ray diffraction (XRD), N₂ adsorption and ICP analysis techniques. The immobilized complex was found to be an effective catalyst for oxidation of cyclohexane using H₂O₂ as an oxidant under mild conditions. A conversion of 45.5% of cyclohexane was obtained with a selectivity of 100% of the cyclohexanone/cyclohexanol mixture when the reaction was run at 60 °C for 12 h in acetonitrile. Decomposition of the complex, which leads to the deactivation of the catalyst, is observed and a decomposition mechanism is discussed.     

Synthesis, Characterization of Ag/MCM-41 and the Catalytic Performance for Liquid-phase Oxidation of Cyclohexane

Nano-scale silver supported mesoporous molecular sieve Ag/MCM-41 was directly prepared by one-pot synthesis method. The prepared sample was characterized by XRD, TEM, and N₂ sorption. The results showed that the sample of Ag/MCM-41 had no appreciable incorporation of silver into the mesoporous matrix of MCM-41 with good crystallinity, and silver nanoparticles were dispersed inside or outside of the channels in the mesoporous host. The catalytic performance of the sample for the cyclohexane liquid-phase oxidation into cyclohexanone and cyclohexanol by oxygen in the absence of solvents without inducing agents was investigated. The 83.4% selectivity to cyclohexanol and cyclohexanone at 10.7% conversion of cyclohexane was obtained over Ag/MCM-41 catalyst at 428 K for 3 h. The turn over numbers (TONs) of Ag/MCM-41 was up to 2946. The catalytic activity of Ag/MCM-41 was also compared with Ag/TS-1 as well as Ag/Al₂O₃. The results indicated that Ag/MCM-41 showed superior activity to both Ag/TS-1 and Ag/Al₂O₃. A calcined Ag/MCM-41 was found to be an efficient catalyst for the cyclohexane oxidation into cyclohexanol and cyclohexanone using oxygen as oxidant.     

Regeneration behaviors of Fe/Si‐2 and Fe–Mn/Si‐2 catalysts for C2H6 dehydrogenation with CO2 to C2H4

The catalytic performance of Fe/Si‐2 and Fe–Mn/Si‐2 catalysts for conversion of C₂H₆ with CO₂ to C₂H₄ was examined in a continuous‐flow and fixed‐bed reactor. The results show that the Fe–Mn/Si‐2 catalyst exhibits much better reaction activity and selectivity to C₂H₄ than those of the Fe/Si‐2 catalyst. Furthermore, the coking–decoking behaviors of these catalysts were studied through TG. The catalytic performances of the catalysts after regeneration for conversion of C₂H₆ or dilute C₂H₆ in FCC off‐gas with CO₂ to C₂H₄ were also examined. The results show that both activity and selectivity of the Fe–Mn/Si‐2 catalyst after regeneration reached the same level as those of the fresh catalyst, whereas it is difficult for the Fe/Si‐2 catalyst to refresh its reaction behavior after regeneration. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of iron on Cu/SiO2 catalysts for the dehydrogenation of cyclohexanol to cyclohexanone

At the temperature range of 250–390°C, the addition of iron to Cu/SiO₂ catalyst increased the conversion and the selectivity of cyclohexanone. The iron incorporation into Cu/SiO₂ catalyst enhanced the reduction temperature of copper oxide, increased the dispersion of copper metal and decreased the selectivity of cyclohexene. Copper was enriched on the surface of the used metal catalyst compared to that in freshly calcined or reduced catalyst. Unlike Cu dispersed on bulk iron oxide, the Cu-Fe dispersed on silica showed negligible amount of phenol formation, thus keeping the selectivity of cyclohexanone very high even at high reaction temperatures. The Fe³⁺ ion in the reduced Cu/Fe/SiO₂ catalyst resulted in a significant resistance of the Cu particle to sintering and a decrease in the selectivity of phenol arisen from the magnetite.     

锡卟啉的合成及其绿色催化氧气氧化环己烯

考察催化剂金属锡次卟啉二甲酯催化氧化环己烯的反应性能。探讨了在催化氧化过程中,反应温度、压力、时间、催化剂用量等因素对环己烯转化率和产物选择性的影响,并结合GC-MS在线分析检测。结果表明,当温度100℃、压力0.8 MPa、时间7 h、催化剂用量0.5 mg(7.6×10-4mmol)、环己烯10 mL(98 mmol)的条件下,环己烯的转化率达84%,相应产物2-环己烯-1-醇和2-环己烯-1-酮的总选择性为94%,并对该反应的催化氧化反应机理进行了初步研究。     

十聚钨酸季铵盐催化环己醇合成环己酮

以十聚钨酸季铵盐([Bmim]4 W10 O32)为催化剂,30%H2O2为氧化剂,研究环己醇催化氧化生成环己酮的反应,考察反应时间、反应温度、30%H2O2和催化剂用量的影响.结果表明,在80℃、催化剂用量0.065 mmol、30%H2O2用量75 mmol、环己醇用量50 mmol和回流反应6 h的条件下,环己醇...     

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%.     

Cobalt molybdenum oxide catalysts for selective oxidation of cyclohexane

Oxidation of cyclohexane has been carried out using molecular oxygen over cobalt molybdenum oxide (CoMoO₄) catalysts in solvent free conditions. The catalysts were prepared using citrate method with three different molar ratios of Co:Mo, 1:1, 1:2, and 2:1 along with individual oxides for comparative studies. While all the catalysts showed significant activity and selectivity, CoMoO₄ with 1:1 ratio showed the best performance compared to the others with a conversion of 7.38%, with selectivity to cyclohexanol and cyclohexanone (KA oil) of 94.3%, in 1 h. The performance of the catalyst, has been studied as a function of oxygen pressure, reaction temperature, and catalyst loading. It was observed that the catalyst deactivates during the course of the reaction. The reasons for deactivation and methods for restoring the activity have been studied. A kinetic model is presented that captures the complex kinetics and matches well with the experimental data. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4384–4402, 2016     

Enhanced photocatalytic degradation of tetramethylammonium on silica-loaded titania

Photocatalytic degradation (PCD) of tetramethylammonium (TMA) in water was studied using both pure TiO₂ and silica-loaded TiO₂ (Si–TiO₂). Use of Si–TiO₂ catalyst prepared from commercial TiO₂ powder by a simple method developed in this work enhanced the PCD rate of TMA considerably. The Si/Ti atomic ratio of 18% was found to be an optimum in photoactivity and the calcined sample was more efficient than the uncalcined one. Several factors were noted to be responsible for the higher photoefficiency of Si–TiO₂ catalyst. Si–TiO₂ calcined at 700 °C did not show any sign of change in the crystalline structure from that of uncalcined pure TiO₂. The increased thermal stability of Si–TiO₂ enabled the bulk defects to be removed at high temperatures without forming the inactive rutile phase, which may partly contribute to the higher photoactivity. The most outstanding characteristics of Si–TiO₂ is its surface charge modification. Loading silica on to a titania surface made the surface charge highly negative, which was confirmed by zeta potential measurements. The enhanced electrostatic attraction of cationic TMA onto the negatively charged Si–TiO₂ surface seems to be the main reason for the enhanced photoactivity of Si–TiO₂. As a result of this surface charge change, the TMA PCD rate with Si–TiO₂ exhibited a maximum around pH 7 whereas the PCD with pure TiO₂ was minimized at pH 7. The X-ray photoelectron spectroscopic analysis showed the formation of SiO_x on the TiO₂ surface but the diffuse reflectance UV spectra indicated no significant difference in the band gap transition between pure TiO₂ and Si–TiO₂. In addition, the diffuse reflectance IR spectra showed the presence of more surface OH groups on Si–TiO₂ than on pure TiO₂, which may also contribute to the higher photoactivity of Si–TiO₂ through generating more OH radicals upon UV illumination.     

Selective decomposition of cyclohexyl hydroperoxide by copper ion-containing quaternary ammonium salts in alkali-free medium

A novel catalytic system composed of quaternary ammonium salts and copper (II) chloride was prepared. The catalyst showed high conversion and selectivity in the decomposition of cyclohexyl hydroperoxide to cyclohexanol and cyclohexanone (K/A oil) at room temperature in alkali-free medium. 93% conversion with 96% selectivity for cyclohexanone and cyclohexanol could be obtained.     

Novel Fe‐based complex oxide catalysts for hydroxylation of phenol

Novel catalysts for the hydroxylation of phenol, Fe–Si–O, Fe–Mg–O and Fe–Mg–Si–O complex oxides, have been synthesized by a coprecipitation method. X‐ray diffraction studies show that MgFe₂O₄ crystallites with spinel structure are formed in Fe–Mg–Si–O and Fe–Mg–O complex oxides and the crystallite size of the metal oxide or complex oxide is reduced after addition of Si. In the hydroxylation of phenol with hydrogen peroxide, Fe‐based complex oxides exhibit high activities after a short induction period. The phenol conversion is improved when silicon is introduced into the Fe‐based complex oxides, and formation of MgFe₂O₄ crystals with spinel structure in the catalysts increases the diphenol selectivity. The addition of a little acetic acid to the reaction liquid can shorten the induction period effectively. Under the same reaction conditions, phenol conversion and diphenol selectivity over the Fe–Mg–Si–O catalyst are close to those over TS‐1, and furthermore, the reaction time is more than ten times shorter as compared to TS‐1. The reaction mechanism of the hydroxylation of phenol on the catalysts has been studied, and a free‐radical mechanism initiated by the formation of phenoxy free radicals is suggested. This revised version was published online in August 2006 with corrections to the Cover Date.     

Study of Mn-based Catalysts for Oxidative Dehydrogenation of Cyclohexane to Cyclohexene

The gas-phase oxidative dehydrogenation (ODH) of cyclohexane to cyclohexene in the presence of molecular oxygen has been studied over various Mn-based catalysts. It is found that LiCl/MnO_x/PC (Portland cement) catalyst exhibits the highest catalytic performance, and a 42.8% cyclohexane conversion, 58.8% cyclohexene selectivity and 25.2% cyclohexene yield can be achieved under 600 °C, 20,000 h⁻¹ and C₆H₁₂/O₂/N₂=14/7/79. There are good correlations between the selectivities to cyclohexene and the electrical conductivities of Li doped Mn-based catalysts, from which it is deduced that the non-fully reduced oxygen species (O₂⁻, O₂²⁻, O⁻) involved in a new phase of LiMn₂O₄ might be responsible for the high selectivity toward cyclohexene, whereas the Mn₂O₃ crystal phase results in the CO_x formation. The selectivity to cyclohexene increases with increasing molar ratio of Li to Mn in LiCl/MnO_x/PC.     

环己烷在Au-Co/SBA-15上选择性氧化的研究

以沉积-沉淀法制备了Au-Co/SBA-15催化剂,在没有任何有机溶剂或助剂的条件下,研究了以空气为氧化剂的环己烷选择性氧化。当Au-Co/SBA-15催化剂中金的质量百分含量为1.0%,催化反应在423 K 3.0 MPa下进行120 m in时,催化效果最好,此时环己烷的转化率为22.7%,环己酮和环己醇的总选择性为95.2%,酮醇比为2.9,且催化剂重复使用五次后活性基本不变。     

Preparation of Titanium-Containing Carbon–Silica Composite Catalysts and Their Liquid-Phase Epoxidation Activity

Titanium-containing catalysts have been prepared by two different post-synthesis methods using activated carbon and carbon-silica composite as catalyst supports. They have been applied to the liquid-phase epoxidation of cyclohexene with tert-butyl hydroperoxide (TBHP) and H₂O₂. The carbon-silica composite catalyst showed a high conversion and selectivity to epoxide compared to the Ti-carbon catalyst and silica-based catalysts for the cyclohexene epoxidation with H₂O₂. The highest values of cyclohexene conversion and epoxide selectivity were obtained with the carbon-silica composite catalyst having a titanium content of 3 wt%.     

环己酮、环己醇制备技术进展

介绍了制备环己醇和环己酮两条工业化路线：(1)通过环己烷氧化制备环己醇和环己酮;(2)通过环己烯水合制备环己醇。还特别介绍了近年来环己烷氧化反应催化剂方面的进展,包括光氧化催化剂,纳米催化剂,Gif催化剂,仿生催化剂,沸石催化剂以及复合催化剂等。并探讨了环己醇和环己酮工业化制备技术将来研究的方向。     

氯取代基对四苯基卟啉Co~(2+)/M_n~(2+)/Cu~(2+)催化氧化环己烷反应的影响

以四苯基金属络合物(Mn2+/Co2+/Cu2+)为对比催化剂,以环己烷转化率、醇酮的选择性为指标,考察研究氯取代基对四苯基卟啉金属络合物(Mn2+/Co2+/Cu2+)催化氧化环己烷反应的影响,实验采用反应压力为1.0MPa、催化剂浓度不变,空气流量控制在0.10~0.12/(m3·h-1)之间,重点考查了反应时间、反应温度、金属卟啉种类等因素对催化氧化环己烷反应的影响。实验结果表明:(1)取代基(单氯)对四苯基金属卟啉催化氧化环己烷反应活性影响较小;取代基(单氯)对四苯基金属卟啉催化氧化环己烷反应时,目标产物--环己醇和环己酮选择性影响也较小;(2)络合三种金属中,催化活性的大小为Co2+Cu2+Mn2+,目标产物-环己醇和环己酮选择性顺序:Cu2+Mn2+Co2+,当以TCPPCu、TPPMn为催化剂时,醇酮的选择性达90%以上,当以TPPCo、TCPPCo、TPPCu、TCPPMn为催化剂时,醇酮的选择性达85%以上;(3)在所考察的6种催化剂中,较佳催化剂有TPPCo和TCPPCo,其相应的反应条件为:1TPPCo作催化剂时,反应温度150~155℃,反应时间50~60min,转化率达到8%以上,选择性达到86%以上;2TCPPCo作催化剂时,反应温度155℃,反应时间60min,转化率达9%以上,选择性为86%以上。     

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.     

Oxidation of Cyclohexane with Molecular Oxygen Catalyzed by SiO2 Supported Palladium Catalysts

The di(ethylthio)ethane palladium (A) and di(ethylthio)propane palladium (B) complexes have been immobilized on the surface of silica gel and these catalyst systems are shown to serve as effective supported Pd catalysts for cyclohexane oxidation with O₂ under solvent free condition. The supported catalyst A provides best results (overall ca. 16.2% conversion, with a selectivity of 72 or 24% for cyclohexanol or cyclohexanone, respectively, which are further promoted in the presence of 2-pyrazinecarboxylic acid which acts as a co-catalyst (overall ca. 21.2% conversion).