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1.
Mixed molybdenum oxides are widely used catalysts for propylene oxidation to acrolein or acrylic acid or for methanol oxidation in the gas phase. In the present study, however molybdenum oxides exhibited an epoxidation activity in the gas phase. To achieve this activity, the oxidation state, particle sizes and accessibility of molybdenum oxides are needed to be controlled. Such active molybdenum species can be prepared by PVD deposition of molybdenum nanorods and their subsequent oxidation in a controlled atmosphere. Accordingly, monoclinic MoO2 particles with a diameter of < 10 nm can be prepared, which exhibit 42% selectivity to propylene oxide (the byproducts of the oxidation being mainly acrolein and acetone). In comparison, molybdenum-containing catalysts prepared by traditional impregnation methods exhibited practically zero epoxidation activity in gas-phase epoxidation of propylene. 相似文献
2.
钼基催化剂在烯烃液相环氧化反应中的应用研究进展 总被引:1,自引:1,他引:0
介绍了钼络合物催化剂、固载化的钼络合物催化剂及MoO3基的固体钼催化剂在烯烃液相环氧化反应中的应用。以有机过氧化物为氧化剂时,不同的钼基催化剂均表现出很好的催化性能,其中络合物中的配体对其催化性能有很大影响,并且可以通过引入手性配体实现对烯烃的不对称环氧化,而固体钼催化剂的性能则与载体上钼物种的种类密切相关。但绝大多数钼催化剂对H2O2参与的环氧化反应没有活性,开发对H2O2有催化活性的钼基催化剂是一个重要的研究方向。 相似文献
3.
《Journal of Catalysis》2007,245(1):55-64
Epoxy resins were polymerised using molybdenum ethoxide and 2-ethylhexanoate as polymerisation initiators. The thermosets thus obtained are useful epoxidation catalysts for a variety of alkenes, including propene with tert-butyl hydroperoxide as an oxidant. To investigate the long-term performance of these resins, they were used repeatedly in up to 120 reactions without any reconditioning. Compared with other catalyst systems based on organic polymers, they reveal unprecedented long-term activities over periods of months so that catalyst lifetimes of years can be expected. Di-, tri-, tetra- and oligofunctional epoxy resin monomers were used and compared. The catalytic performance of the thermosets strongly depends on the resin type and the polymerisation initiator. Promising results were obtained with monomers bearing 3 or 4 glycidyl groups in combination with Mo(OEt)5 as an initiator. Metal leaching, determined by sensitive atomic spectroscopic techniques, is extremely low. Inorganic–organic hybrid catalysts can be easily prepared by adding inorganic components such as silicagel to the liquid resins, followed by polymerisation. 相似文献
4.
Kenji Wada Naoki Watanabe Teruyuki Kondo Take-aki Mitsudo 《Chemical engineering science》2008,63(20):4917-4923
Silsesquioxanes containing tetrapodal titanium species and alkenylsilyl groups were immobilized onto dimethylsilyl-functionalized silica having mesopores by chemical tethering via hydrosilylative reaction in the presence of a Pt catalyst. The immobilized catalysts showed higher activity than their corresponding homogeneous catalyst towards the epoxidation of cyclooctene by tert-butylhydroperoxide, probably because of the improvement of the micro-environment around the titanium center. The reaction was found to be truly heterogeneous, since no further reaction proceeded after the separation of the catalyst by filtration. These catalysts also showed excellent catalytic activity for the epoxidation using hydrogen peroxide as an oxidant, while the parent homogeneous catalysts did not show any activity at all. 相似文献
5.
《Journal of Catalysis》2005,229(2):513-524
An olefin epoxidation Ti catalyst has been optimised by means of high-throughput experimentation involving materials synthesis, postsynthesis treatments, and catalytic testing. Softcomputing techniques for advanced experimental design have been used. The variables explored in the hydrothermal synthesis of Ti-silicate-based catalysts were: concentration of OH−, titanium, and surfactant. The probe reaction employed for the optimisation was the solvent-free epoxidation of cyclohexene, with tert-butylhydroperoxide as oxidant. The different catalyst groups detected by clustering analysis were studied by XRD and UV diffuse reflectance. Ti-mesoporous MCM-41 and MCM-48 molecular sieves were among the most active catalysts. The best performing catalysts were tested for epoxidation of different linear olefins. 相似文献
6.
7.
《Catalysis communications》2007,8(7):987-990
Commercially available molybdenum(VI) compounds are shown to be good catalysts in the epoxidation of cyclooctene with the urea-hydrogen peroxide adduct (UHP) in the ionic liquid 1-n-butyl-3-methylimidazolium hexafluorophosphate, [bmim]PF6. The cyclooctene oxide was isolated by simple extraction with organic solvent and the ionic liquid-catalyst mixture recycled and reused. 相似文献
8.
Xuemei Huang Xiangkai Fu Ziyong Jia Qiang Miao Guoming Wang 《Journal of Porous Materials》2013,20(4):809-820
Chiral salen Mn(III) complex was axially immobilized onto phenoxy-modified organic polymer-inorganic hybrid material layered crystalline aluminium oligo-styrenyl phosphonate-hydrogen phosphate. The prepared catalysts exhibited excellent activities and enantioselectivities for asymmetric epoxidation of unfunctionalized olefins with m-chloroperbenzoic acid as oxidant, especially for the epoxidation of α-methylstyrene (conversion: up to 99 %; ee: exceed 99 %). A point worth emphasizing is that the heterogeneous catalysts afforded remarkable increases of conversions and ee values without adding axial base N-methylmorpholine N-oxide for the asymmetric epoxidation of olefins. The catalyst can be easily recovered and reused with slightly decrease of activity and enantioselectivity after seven cycles. Delightedly, this novel heterogeneous catalyst could also be efficiently used in large-scale reactions with the enantioselectivity being maintained at the same level, which provided the potentiality for application in industry. 相似文献
9.
10.
Hydrodesulfurization of dibenzothiophene over supported and unsupported molybdenum carbide catalysts
Hea Kyung Park Du Soung Kim Kyung Lim Kim 《Korean Journal of Chemical Engineering》1998,15(6):625-630
A series of γ-Al2O3 supported molybdenum carbides [carbided Mo/γ-Al2O3 (MCS), Co-Mo/γ-Al2O3 (CMCS), and Ni-Mo/γ-Al2O3 (NMCS)] and unsupported molybdenum carbide (MCUS) were prepared by the temperature-programmed carburization of their corresponding
molybdenum nitrides with 20 % CH4/H2. XRD and SEM studies show that unsupported molybdenum carbide catalyst possesses a typical crystalline Mo2C (FCC structure), while supported molybdenum carbide catalysts possess highly dispersed surface molybdenum carbide species
on an alumina oxide support. The results of dibenzothiophene (DBT) hydrodesulfurization over molybdenum carbide catalysts
show that the reactivity is strongly dependent on the type of catalyst. Supported molybdenum carbide catalysts possess a higher
reactivity than the unsupported molybdenum carbide catalyst. In addition, Co or Ni promoted, supported molybdenum carbide
catalyst possesses a higher reactivity than the unpromoted, supported molybdenum carbide catalyst. The reactivity, which is
also dependent on the reaction conditions, increases with increasing reaction temperature and pressure and contact time. The
CO uptakes of the molybdenum carbide catalysts correlate well with overall activity (total rate) for DBT hydrodesulfurization.
The major reaction product is biphenyl, with cyclohexylbenzene next in abundance regardless of the type of catalysts and reaction
conditions. It was also found that the molybdenum carbide catalysts exhibit stable initial reactivity due to the stable and
weak acidic characteristics of these catalysts. 相似文献
11.
12.
Jerry F. Kriz Hiromichi Shimada Yuji Yoshimura Nobuyuki Matsubayashi Akio Nishijima 《Fuel》1995,74(12):1852-1857
A series of nickel-containing catalysts was prepared by a sequence of impregnation and calcining steps using a γ-alumina support. The calcined catalysts were reduced in a flow of hydrogen and mixtures of hydrogen with hydrogen sulfide. Both the calcining temperature and nickel loading strongly influenced the hydrogenation activity. The changes in surface species which resulted from some of the preparation steps were identified by spectroscopy. The catalysts containing nickel without molybdenum were quickly poisoned by sulfur, but a certa in sulfur tolerance was achieved by a two-step impregnation and calcining procedure. Improved hydrogenation activity and high hydrogenation vs. hydrocracking selectivity of nickel—molybdenum catalysts were obtained with relatively low loading of molybdenum and high loading of nickel. A three-step impregnation and calcining procedure appeared to produce the most effective catalysts. 相似文献
13.
A novel approach to the epoxidation of unsaturated rubbers in a reactive processing equipment is presented for the first time in this paper. The effects of the structures of unsaturated rubbers and catalysts on the epoxidation reaction were examined. The experimental results show that the reactivity of three typical unsaturated rubbers follows the decreasing order: ethylene‐propylene‐diene rubber (EPDM) > butadiene rubber (BR) > styrene‐butadiene rubber (SBR). No obvious further oxidation side reaction occurs during the epoxidation of EPDM and BR, while SBR has a significant degradation during reaction. Moreover, investigation of the catalytic system composed of tert‐butyl hydroperoxide (TBHP) and three different molybdenum compounds reveals that a blue molybdenum compound (Mo‐b), which is the product of the reaction of hydrogen peroxide (30% aqueous solution) with an excess of molybdenum powder, gives the highest catalytic activity and the highest efficiency of TBHP. 相似文献
14.
A set of transition-metal-free heterogeneous catalysts for the epoxidation of alkenes with hydrogen peroxide was studied by means of high-throughput experimentation. The catalysts were tested with a range of substrates. Gallium oxide displayed the highest epoxidation activity with all tested alkenes, followed by Ga-MCM-41. The reaction conditions were optimised by investigating the effect of the solvent in which the epoxidation takes place. Considerable improvements in the epoxide yields were obtained in the processes catalysed by Al-MCM-41, Ga-MCM-41 and zeolite USY(2.6). This work confirms the versatility of HTE for studying catalytic systems. 相似文献
15.
《Catalysis communications》2007,8(1):57-64
Au, Ag and Au–Ag catalysts on different supports of alumina, titania and ceria were studied for their catalytic activity of ethylene oxidation reactions. An addition of an appropriate amount of Au on Ag/Al2O3 catalyst was found to enhance the catalytic activity of the ethylene epoxidation reaction because Au acts as a diluting agent on the Ag surface creating new single silver sites which favor molecular oxygen adsorption. The Ag catalysts on both titania and ceria supports exhibited very poor catalytic activity toward the epoxidation reaction of ethylene, so pure Au catalysts on these two supports were investigated. The Au/TiO2 catalysts provided the highest selectivity of ethylene oxide with relatively low ethylene conversion whereas, the Au/CeO2 catalysts was shown to favor the total oxidation reaction over the epoxidation reaction at very low temperatures. In comparisons among the studied catalysts, the bimetallic Au–Ag/Al2O3 catalyst is the best candidate for the ethylene epoxidation. The catalytic activity of the gold catalysts was found to depend on the support material and catalyst preparation method which govern the Au particle size and the interaction between the Au particles and the support. 相似文献
16.
Reactant shape selectivity of supported titanium catalysts for epoxidation of cyclohexene and 2-hexene has an excellent correlation with the pore diameter of the catalysts. With titanosilicate the preference to cis isomer epoxidation is small compared to TiO2-SiO2 probably because of the restriction of its diffusion imposed by the zeolite micropore structure. 相似文献
17.
The effects of dispersed catalysts on coal liquefaction under hydrogen pressure were studied using small autoclaves. The catalysts were generated in situ by addition of elemental sulphur plus an oil-soluble carboxylic salt of either iron or molybdenum. Finely divided catalysts of relatively high activity were generated by this method. Residues isolated after liquefaction with added iron carboxylate and sulphur contained pyrrhotite, which is proposed to be the catalytically active species. The prime role of sulphur is to form pyrrhotite in combination with the iron. Addition of sulphur alone did not increase conversion. This method of catalyst preparation seems useful for further scientific study of the relationship between sulphur, metal sulphide catalysts and liquefaction activity. 相似文献
18.
《Applied Catalysis A: General》2007,316(2):142-151
It was found that silica-supported molybdenum oxide was high effective for the epoxidation of propylene among various silica-supported metal oxides. The post-catalytic bed volume played an important role in its formation. On a MoOx/SiO2 with 0.255 mmol/g-SiO2, a propylene conversion of 17.6% and a PO selectivity of 43.6% were obtained at 5 atm, 573 K and flow rates of C3H6/O2/He = 10/5/10 cm3 min−1. The characterization studies indicated that crystalline MoO3 nano-particle species was more effective for propylene epoxidation to PO than molecularly dispersed Mo oxide species. The reaction mechanism of propylene epoxidation on MoOx/SiO2 catalysts is hypothesized to involve gas-phase radicals generated at relatively low temperature by the dispersed molybdenum oxide species. These radicals participated in homogeneous reactions with molecular oxygen to produce propylene oxide. 相似文献
19.
Information on the production and consumption of molybdenum and tungsten in the world and in Russia is provided. The lowering
of domestic consumption of these metals in the Russian industry is demonstrated. The use of these metals in catalysts manufacturing
in Russia is considered. The assortment of domestic molybdenum- and tungsten-containing catalysts is discussed, and their
consumption is estimated. The current demand for molybdenum and tungsten in catalyst manufacturing is small because of the
high impact of imported catalysts and low level in the development of chemical catalytic processes. Certain applications of
molybdenum- and tungsten-containing catalysts are considered. It is shown that the consumption of molybdenum and tungsten
in the manufacturing of high-added value products (catalysts) may grow at the expense of the replacement of imported catalysts
by competitive domestic molybdenum- and tungsten-containing catalysts and their use in new processes. 相似文献