环己烷催化氧化制环己酮的MCM-41催化剂研究

以十六烷基三甲基溴化铵为模板剂,正硅酸乙酯为硅源,采用水热合成法制备纯MCM-41分子筛和掺杂不同金属离子的MCM-41分子筛,并采用等体积浸渍法将一定量的金属离子负载在纯MCM-41分子筛内表面上,制备了负载型和掺杂型2类不同的MCM-41分子筛催化剂.分别考察了负载和掺杂的金属种类、金属Cr负载和掺杂量等对环己烷氧化制环己酮中的催化活性和选择性的影响.研究表明:采用掺杂制备的MCM-41分子筛催化剂活性明显高于负载型MCM-41分子筛催化剂;Cr掺杂量增加,虽然环己烷氧化转化率增加,但产物选择性下降;掺杂Cr的MCM-41分子筛催化剂,用于环己烷氧化制环己酮,在Si与Cr摩尔比为50以下、反应温度75℃、H2O2与环己烷摩尔比为1.2的条件下,环己烷的转化率可达60%左右,环己酮和环己醇的总选择性可达94%以上.     

Epoxidation of β-ionone using molecular oxygen over Pt/MCM-41 catalyst under mild conditions

The epoxidation of β-ionone over the Pt/MCM-41 catalyst using molecular oxygen in the liquid phase had been studied. The results indicated that the β-ionone was catalytically oxidized to 5,6-epoxy-β-ionone, 4-oxo-β-ionone, 4-hydroxy-β-ionone and dihydroactinidiolide using molecular oxygen as the sole oxidant. The effects of solvent, content of Pt, reaction temperature and time on the catalytic activity and product selectivity had also been investigated in detail.     

Selective oxidation of benzaldehyde by molecular oxygen over molybdovanadophosphoric acid supported MCM-41

A series of molybdovanadophosphoric acid (MVPA) supported on mesoporous silica was synthesized by an incipient wetness impregnation method. The catalysts were characterized by nitrogen adsorption?Cdesorption, X-ray powder diffraction, Fourier-Transform Infra red spectroscopy (FT-IR), UV?CVis Diffused reflectance spectroscopy (UV?CVis DRS), Temperature programmed reduction (TPR) and ³¹P MAS Nuclear magnetic resonance(NMR) study. The characterization data reveals the incorporation of vanadium in phosphomolybdic acid and retention of intact Keggin ion on the support. The catalytic activities were evaluated for oxidation of benzaldehyde using molecular oxygen as oxidant as the new green reaction system. Among all the promoted catalysts, 50wt% molybdovanadophosphoric acid supported on MCM-41 exhibits highest catalytic activity in oxidation of benzaldehyde, giving 95% conversion. Other oxidants like H₂O₂ and tert-butyl hydrogen peroxide (TBHP) were also tested for benzaldehyde oxidation reaction.     

Liquid-phase oxidation of cyclohexane using Co-P-MCM-41 catalyst

Co-P-MCM-41 catalyst was prepared by introduction of cobalt nitrate and phosphoric acid during gel-preparation for the synthesis of MCM-41. The catalyst, which was found to have very high surface area (995 m²/g), was tested for the one step liquid oxidation of cyclohexane to adipic acid using a semi-batch autoclave reactor (without addition of any promoter and solvent) at 115°C and in a flow of 5 bar of oxygen. The effect of the amount of catalyst on the induction time, catalytic conversion of cyclohexane, and selectivity to adipic acid was investigated. Depending on the amount of catalysts used in the reaction (from 0.1 to 3.0 g), an induction period from about 100 min to less than 10 min, cyclohexane conversion from 30 to 99%, and a selectivity to adipic acid from 15 to 40 %, could be achieved using Co-P-MCM-41 as the catalyst.     

Direct vapor phase oxidation of propylene by molecular oxygen over MCM-41 or MCM-22 based catalysts

Ti and Al containing MCM-41 (Al-c-MCM-41 and Al-Ti-c-MCM-41) have been synthesized and tested for direct oxidation of propylene with molecular oxygen. Al-Ti-c-MCM-41 is more effective than Al-c-MCM-41, while no product was formed for MCM-41 alone. It is also found that MCM-22 with Si/Al₂ ratio of 30 and Na/SiO₂ ratio of 0.18 is active for the reaction and a highest PO yield of 11.3% was obtained at 573 K.     

A highly active Au/Al2O3 catalyst for cyclohexane oxidation using molecular oxygen

The selective oxidation of cyclohexane to cyclohexanone and cyclohexanol has been investigated over Au/Al₂O₃ catalysts using molecular oxygen in a solvent-free system. The catalysts were prepared by a modified direct anionic exchange method and characterized by AAS, N₂ adsorption and TEM. The results showed that the catalytic performance of Au/Al₂O₃ is very high in terms of turnover frequency. Moreover, the nano-size effect of gold is also reported in the reaction.     

Synthesis of heterogeneous copper complex catalyst for oxidation of cyclohexane using molecular oxygen

Binuclear macrocyclic copper complex was synthesized and bonded ionically to the montmorillonite clay to enhance thermal stability upto 600°C. The oxidation of cyclohexane using molecular oxygen in the absence of initiators, promoters and coreactants has been studied in the temperature range 145–190°C. The overall cyclohexane conversion was 21% at 180°C and cyclohexanone, the major product with 71% selectivity. The experimental data were analyzed against kinetic scheme proposed and the rate constants determined using Genetic Algorithm.     

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     

In situ oxidation for stabilization of Fe/MCM-41 catalyst prepared by metal organic chemical vapor deposition

Oxygen has been found to be a key factor in the process of metal organic chemical vapour deposition (MOCVD) to stabilize the iron catalyst supported on MCM-41, particularly in the acidic aqueous reaction. Such stabilization is achieved by in situ oxidation of iron, which intercalates oxygen atoms into the framework of both siliceous and ferric oxides by developing Fe–O–Si and Fe–O–Fe bonds, respectively. This stable Fe/MCM-41 catalyst shows an excellent mineralization efficiency of orange II of ∼85% and an extremely low iron leaching concentration of ∼0.17 mg/L. The catalyst maintains its excellent catalytic activity after multiple reaction runs under acidic aqueous medium.     

杂原子MCM-41分子筛对过氧化氢液相氧化环己烷的研究

分别考察了反应温度、过氧化氢用量及加入方式等因素对Cr、Fe和Ce改性后的杂原子MCM-41分子筛催化剂液相催化氧化环己烷制取环己酮反应的影响。研究结果表明，Cr-MCM-41〖JP〗催化剂具有较好的催化活性。选择适当的反应温度、过氧化氢用量和加入方式可以有效提高环己烷转化率和过氧化氢利用率。在70 ℃和n(C₆ H₁₂)∶n(H₂O₂)=1∶2条件下，采用两次加入过氧化氢的方式，环己烷转化率为33.7％，酮醇总选择性97.2％，n(环己酮)∶n(环己醇）＝1.99，过氧化氢利用率37.1%。     

Co-M/Al2O3上环己烷的选择性氧化研究

采用溶胶-凝胶法制备了Co-M/Al₂O₃(M=Cu，Zn，Ni)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。所制备四种催化剂的活性为Co-Ni/Al₂O₃ >Co/Al₂O₃ >Co-Zn/Al₂O₃ >Co-Cu/Al₂O₃。在Co-Ni/Al₂O₃中Co、Ni的质量分数分别为4.0%和3.0%时活性最好。以Co-Ni/Al₂O₃为催化剂，在4.5 MPa、443 K下反应120 min，环己烷转化率达9.9%，环己酮和环己醇的总选择性达94.6%，n(酮)∶n(醇)为2.8。Co-Ni/Al₂O₃催化剂连续使用五次后活性基本不变。     

Methanol synthesis over Pd/SiO2 with narrow Pd size distribution prepared by using MCM-41 as a support precursor

All silicious MCM-41 was investigated as a support or a support precursor for Pd/SiO₂ and prepared catalysts were tested for methanol synthesis from CO and H₂. The methods of Pd loading on the MCM-41 were impregnation, seed impregnation and chemical vapor deposition (CVD). For both impregnations, most Pd existed outside of the pore as large particles, and only a small part of Pd was inserted into the pore of MCM-41 retaining the initial structure. On the contrary, in the catalyst prepared by CVD method, the MCM-41 structure was completely destroyed to become amorphous SiO₂. Yet the average Pd particle size in this catalyst was smaller and its distribution was narrower than those of the catalysts prepared by impregnation methods. In the methanol synthesis from CO hydrogenation the catalyst prepared by CVD showed higher methanol selectivity than other MCM-41-derived catalysts. This result was considered to be due to the more uniform distribution of the Pd particle size.     

Propylene epoxidation over Ti/MCM-41 catalysts prepared by chemical vapor deposition

Ti-containing mesoporous catalysts were prepared by chemical vapor deposition (CVD) of TiCl₄ on silica MCM-41 in the 700–900 °C temperature range. These samples were characterized (with XRD, ICP, nitrogen adsorption, FT-IR, ESCA, and TEM) and evaluated for the epoxidation of propylene with two alkyl hydroperoxides. The increase of CVD temperature resulted in the decrease of titanium content, catalyst hydroxyl population, crystallinity, and surface area. Catalyst selectivity to the desired product – propylene oxide – was highly sensitive to the deposition temperature. The best Ti/MCM-41 catalyst was prepared at the temperature of 800 °C, which had the maximum propylene oxide yield of 94.3%.     

The oxidation of sulfide to sulfoxide on Ti-complex/MCM-41 catalyst

The heterogeneous Kagan-type catalyst was prepared by an in situ method using MCM-41 as support. The influence of the incorporation process on the structure of MCM-41 was studied using XRD, FT-IR, UV-vis, ²⁹Si-MAS-NMR and N₂ adsorption–desorption. The obtained materials showed a definite catalytic activity on the oxidation of sulfide to sulfoxide in the medium containing dichloromethane (solvent) and H₂O₂ or TBHP (oxidant).     

Selective catalytic reduction of NOx in lean-burn engine exhaust over a Pt/V/MCM-41 catalyst

The activities of Pt supported on various metal-substituted MCM-41 (V-, Ti-, Fe-, Al-, Ga-, La-, Co-, Mo-, Ce-, and Zr-MCM-41) and V-impregnated MCM-41 were investigated for the reduction of NO by C₃H₆. Among these catalysts, Pt supported on V-impregnated MCM-41 showed the best activity. The maximum conversion of NO into N₂+N₂O over this Pt/V/MCM-41 catalyst (Pt=1 wt.%, V=3.8 wt.%) was 73%, and this maximum conversion was sustained over a temperature range of 70 °C from 270 to 340 °C. The high activity of Pt/V/MCM-41 over a broad temperature range resulted from two additional reactions besides the reaction occurring on usual supported Pt, the reaction of NO with surface carbonaceous materials, and the reaction of NO occurring on support V-impregnated MCM-41. The former additional reaction showed an oscillation characteristic, a phenomenon in which the concentrations of parts of reactant and product gases oscillate continuously. At low temperature, some water vapor injected into the reactant gas mixture promoted the reaction occurring on usual supported Pt, whereas at high temperature, it suppressed the additional reaction related to carbonaceous materials. Five-hundred parts per million of SO₂ added to the reactant gas mixture only slightly decreased the NO conversion of Pt/V/MCM-41.     

An efficient microwave-assisted Suzuki reaction using Pd/MCM-41 and Pd/SBA-15 as catalysts in solvent-free condition

Palladium catalysts, Pd/MCM-41 and Pd/SBA-15 were prepared by impregnation of an aqueous solution of [Pd(NH₃)₄]Cl₂ on MCM-41 and SBA-15. Palladium contents of Pd/MCM-41 and Pd/SBA-15 are 8.4% and 8.7%, respectively. It has been shown that these catalysts are very suitable to microwave-assisted Suzuki reactions under solvent-free condition. It is also found that the base additives for this reaction are K₂CO₃, Cs₂CO₃ or CsF. Thus, phenylboronic acid and phenyl iodide with Pd/MCM-41 produce biphenyl by microwave irradiation for 10 min in 97.4% yield. Phenyl bromide, instead of phenyl iodide, also proceeds the reaction with phenylboronic acid using Pd/MCM-41 or Pd/SBA-15 yielding biphenyl by microwave irradiation for 10 min in excellent yield. Whereas the reaction of phenyl chloride with phenylboronic acid gives poor yield in same condition. Various aryl iodides and aryl bromides are tested. In this paper our recent results of microwave-assisted Suzuki reaction using Pd/MCM-41 and Pd/SBA-15 under solvent-free condition are described.     

Schiff base complex of Cu immobilized on MCM-41 as reusable catalyst for efficient oxidative coupling of thiols and oxidation of sulfides using hydrogen peroxide

Schiff base complex of copper-functionalized MCM-41 (Cu-complex@MCM-41) was synthesized and used as an efficient and novel heterogeneous catalyst for the oxidative coupling of thiols into corresponding disulfides and oxidation of sulfides to sulfoxides using hydrogen peroxide (H₂O₂) as the oxidant. An aliphatic and aromatic series of sulfides and thiols including various functional groups were successfully converted into corresponding products. The all products were obtained in good to excellent yields. The mesoporous catalyst is characterized by FT-IR spectroscopy, BET, XRD, SEM, EDS and TGA. Recovery of the catalyst is easily achieved by simple filtration and reused for several consecutive runs without significant loss of its catalytic efficiency.     

Pt/MCM-41 catalyst for selective catalytic reduction of nitric oxide with hydrocarbons in the presence of excess oxygen

First results are reported on the use of MCM-41 mesoporous molecular sieve as the support for Pt for the selective catalytic reduction of NO by hydrocarbons in the presence of O₂. MCM-41 provided the highest specific NO reduction rates for Pt as compared with all other supports reported in the literature, i.e., Al₂O₃, SiO₂ and ZSM-5. This revised version was published online in July 2006 with corrections to the Cover Date.     

ZrO2/MCM-41催化的苯乙酮氢转移反应

通过浸渍法分别制备了硅胶(SiO2)、全硅MCM-41介孔分子筛负载ZrO2催化剂,考察其在以异丙醇为氢源,苯乙酮的氢转移反应中的催化性能,并与纯ZrO2进行对比,同时对各催化剂进行XRD、N2吸附-脱附、XPS、吡啶原位吸附红外等表征分析。结果表明:与纯ZrO2相比,负载型催化剂活性明显增加,归因于ZrO2与载体发生强相互作用,形成Si-O-Zr键,使催化剂表面的Zr-OH数目显著增加,出现B酸中心,且L酸中心强度增强。ZrO2/MCM-41的催化活性优于ZrO2/SiO2,可归因为前者中ZrO2的分散程度较高。ZrO2/MCM-41的最佳ZrO2负载量为5%(wt);最佳反应时间8 h;最佳异丙醇和苯乙酮摩尔比为10:1。苯乙酮含吸电子取代基后转化率升高,而含供电子取代基后转化率降低。5%ZrO2/MCM-41的催化活性随重复使用次数增加而逐渐降低。     

不同体系光催化制备纳米Ag/TiO2光催化剂活性比较

以控制中和水解法制备的锐钛矿型纳米TiO2为原料.在不同体系中,通过控制反应初始n(Ag):n(Ti),用直接光催化反应的方法制备了蚋米Ag/TiO2复合先催化剂,并且对产品进行了表征和分析.结果表明,Ag的改性能显著提高光催化效率,乙醇有机溶剂体系和水体系中制得的Ag/TiO2复合光催化剂的光催化活性相差不大,最佳n(Ag),n(Ti)为0.1%.同时与UV光相比在室内自然先作用下得到的Ag/TiO2复合光催化剂表现出更好的活性,40 min甲基橙先催化降解率比蚋米TiO2高约44%.