The sol-gel procedure was applied to obtain powdery materials with different structures and morphology. It was possible to produce almost non-porous silica powder, with an extremely low surface area (ca. 4 m2/g) and very high uniformity of spherical particles as well as materials with various uniformity of particles and different porosity, most likely associated with increasing pore volume. Dependent on the properties of the carrier, the resulting supported vanadium catalysts (VOCl3/AlEt2Cl) showed significant differences concerning activity and stability. It was confirmed that improved hydrophobicity of the carrier’s surface may be useful and improve the activity of the system in the polymerization. It was found that the two-step modification procedure, involving a reaction with alkylaluminum, acts beneficially for the efficiency of supported catalysts. The system supported on sol-gel material with methyl groups, additionally pre-treated with diethylaluminum chloride, showed the highest activity as well as the lowest deactivation rate constant among all those studied. 相似文献
Vanadium oxides, as highly efficiently catalysts, are widely applied in various catalytic reactions, such as the dehydrogenation of light alkanes and epoxidation of alkenes. In this paper, a series of VO x /Al 2 O 3 catalysts were fabricated by the 1-pot method for catalytic propane dehydrogenation. The results indicated that the VO x /Al 2 O 3 catalysts with loading of 10 wt.% vanadium exhibited optimized catalytic performance. The as-prepared catalysts were characterized by N 2 adsorption-desorption, XRD, TEM, H 2 -TPR, and XPS to explore the texture properties, morphology, and electronic environment of vanadium. In addition, several vanadium catalysts were also prepared by the incipient wetness impregnation (IWI) method to compare their catalytic performance with the 1-pot synthesized catalysts. The catalysts synthesized by the 1-pot method exhibited higher selectivity of propylene and longer catalyst lifetime at high propane conversion when compared to the counterpart synthesized by the IWI method. 相似文献
The polymerization of isobutyl vinyl ether by the VCln–AIR3 system was carefully studied. The vanadium components were prepared by the reaction between VCl4 and AlEt3 or n-BuLi as a reducing agent. VCl3·LiCl and VCl2·2LiCl are the effective catalysts for the stereospecific polymerization of isobutyl vinyl ether. When VCl3·LiCl is combined with AlR3, a new catalytic system is formed. The effect of the preparative conditions of the various vanadium component in the AlR3–VCln system shows that the effective vanadium component is trivalent. In the polymerization by VCl3·LiCl–Al (i-Bu)3 system, a change of the polymerization mechanism may occur at Al(i-Bu)3/VCl3·LiCl ratio at around 5. When the ratio is lower than 5, a cationic polymerization by VCl3·LiCl takes place predominantly, while at ratios higher than 5, it is suggested that the polymerization proceeds by means of a VCl3·LiClA–Al(i-Bu)3 complex by a coordinated anionic mechanism. The polymers obtained by these catalysts are highly crystalline. Styrene was also polymerized by using the same catalysts. VCl3·LiCl and VCl3·LiCl–THF complex yielded amorphous polymer by cationic polymerization. When VCl3·LiCl was combined with 6 mole-eq of Al(i-Bu)3, the resulting polystyrene was highly crystalline and had an isotactic structure, while the VCl2·2LiCl–Al(i-Bu)3 (1:6) system yielded traces of polymer of extremely low stereoregularity. The results indicate that the effective vanadium component at Al/V ≧ 6 is trivalent and that the mechanism is a coordinated anionic one. 相似文献
A new class of ethylene polymerization catalysts, namely the bis-(2,4-dimethyl pentadienyl) derivatives of titanium, vanadium, and chromium, have been synthesized and tested. When supported on a variety of inorganic carriers, these compounds yielded 0.2–1.0 million g polymer/g metal/h under typical slurry conditions. Sensitivity to H2 as a molecular weight regulator varied among the three metals, but in the absence of H2 all produced ultrahigh-molecular-weight polyethylene. The molecular weight distribution varied from moderately narrow to very broad (bimodal) depending on the metal and the carrier. Catalyst synthesis and polymer properties are discussed. 相似文献
An active-phase monolayer has been deposited on SiO2 using replacement of the surface OH groups by VOCl3 vapour. The amount of vanadium fixed on the SiO2 surface depends on the initial concentration of the silanol groups and ranges from 3.36 to 1.43%. In combination with diethyl aluminium chloride, the products are active catalysts for ethylene polymerization. The effects of the reaction conditions (the time of catalyst-complex formation, the catalyst life time and the temperature of polymerization) as well as the effect of the vanadium content, the A1:V ratio and the presence of diphenyl magnesium on the activity of the catalyst system have been investigated. The catalyst activity was found to depend strongly on the amount of vanadium fixed on the support surface. The maximum productivity obtained is about 22,000 gPE/g vanadium. Some basic characteristics of the synthesized polymer such as tensile strength, elongation at break, density and crystallization degree are given. 相似文献
A novel carrier of ultradispersed diamond black powder (UDDBP) was used to support metallocene catalyst. Al2O3 was also used as carrier in order to compare with UDDBP. Supported catalysts for ethylene polymerization were synthesized by two different reaction methods. One way was direct immobilization of the metallocene on the support, the other was adsorption of MAO onto the support followed by addition of the metallocene. Four supported catalysts Cp2ZrCl2/UDDBP, Cp2ZrCl2/Al2O3, Cp2ZrCl2/MAO/UDDBP and Cp2ZrCl2/Al2O3/MAO were obtained. The content of the zirconium in the supported catalyst was determined by UV spectroscopy. The activity of the ethylene polymerization catalyzed by supported catalyst was investigated. The influence of Al/Zr molar ratio and polymerization temperature on the activity was discussed. The polymerization rate was also observed. 相似文献
Recent results for synthesis of end-functionalized polymers (EFP) by using olefin metathesis polymerization have been introduced including basic characteristics in ring-opening metathesis polymerization (ROMP) of cyclic olefins and acyclic diene metathesis (ADMET) polymerization for synthesis of conjugated polymers. Several approaches were demonstrated for synthesis of EFP by living ROMP using molybdenum (exclusive coupling with aldehyde) and ruthenium catalysts (sacrificial ROMP, chain transfer). Cis specific (Z selective) ROMPs were achieved by molybdenum, ruthenium, and vanadium catalysts by the ligand modification. The catalytic synthesis of EFP with high cis selectivity has been achieved by combined ROMP with chain transfer by V(CHSiMe3)(N-2,6-Cl2C6H3)[OC(CF3)3](PMe3)2. The ADMET polymerization using molybdenum and ruthenium catalysts afforded defect-free, high molecular weight poly(arylene vinylene)s containing all trans olefinic double bonds. The methods for precise synthesis of EFPs, exhibiting unique optical properties combined with the end groups, were developed. The catalytic one-pot syntheses for EFPs have also been developed. 相似文献
A novel vanadium‐modified (SiO2/MgO/MgCl2)·TiClx Ziegler–Natta ethylene polymerization catalyst with much better catalytic performance is successfully developed. The catalyst is prepared by co‐impregnation of aqueous solution of water‐soluble magnesium and vanadium compounds on SiO2, and a supported thin layer of magnesium and vanadium oxides is formed over the surface of SiO2 after high temperature calcination in dry air, followed by further reaction with titanium tetrachloride to synthesize the magnesium dichloride carrier in situ and to support the titanium species simultaneously. By characterization of the catalysts and the polymers and investigation of the polymerization behaviors, it is found that compared with the original (SiO2/MgO/MgCl2)·TiClx ZN catalyst, the introduction of vanadium species induce improved catalytic performance with 27% higher activity, 48% higher hydrogen response, and 60% higher 1‐hexene incorporation ability with better short chain branch distribution.
Immobilization and activation of a broad range of titanium-, chromium-and nickel-based single-site catalysts for ethylene
polymerization has been carried out using supports of type MgCl2/AlRn(OEt)3 − n, prepared by reaction of AlR3 with adducts of magnesium chloride and ethanol. The spherical particle morphology of the support is retained and replicated
during catalyst immobilization and polymerization, yielding polyethylenes with controlled particle size and morphology. The
single-site nature of these catalysts is also retained, giving polymers with narrow molecular weight distribution. Furthermore,
very high catalyst activities can be obtained as a result of a stabilizing effect of the support, which prevents the rapid
decay in activity often observed in homogeneous polymerization with these catalysts.
The text was submitted by the authors in English. 相似文献
Vanadium oxide catalysts of the monolayer type have been prepared by means of chemisorption of vanadate(V)-anions from aqueous solutions and by chemisorption of gaseous V2O3(OH)4. Using Al2O3, Cr2O3, TiO2, CeO2 and ZrO2, catalysts with an approximately complete monomolecular layer of vanadium(V) oxide on the carrier oxides can be prepared, if temperature is not too high. Divalent metal oxides like CdO and ZnO may already form threedimensional surface vanadates at moderate temperature. The thermal stability of a monolayer catalyst is related to the parameter z/a, i. e. the ratio of the carrier cation charge to the sum of ionic radii of carrier cation and oxide anion. Thus, monolayer catalysts will be thermally stable only under the condition that z/a is not too high (aggregated catalyst) nor too small (ternary compound formation). 相似文献
Slurry polymerizations of ethylene over vanadium catalysts (based on VCl4 and VOCl3) and their MgCl2(THF)2-supported equivalents were studied. Unsupported vanadium catalysts were found to be unstable while the vanadium active sites deposited on the MgCl2(THF)2 complex are stable. A sharply outlined correlation was found between the concentration of vanadium(III) and catalyst productivity. The high activity and stability of the vanadium catalyst when supported on the magnesium complex is attributed to the increase of resistance to reduction of active vanadium(III) to inactive vanadium(II) by an organoaluminium co-catalyst. 相似文献
The polymerization of isobutyl vinyl ether by vanadium trichloride in n-heptane was studied. VCl3 ? LiCl was prepared by the reduction of VCl4 with stoichiometric amounts of BuLi. This type of catalyst induces stereospecific polymerization of isobutyl vinyl ether without the action of trialkyl aluminum to an isotactic polymer when a rise in temperature during the polymerization was depressed by cooling. It is suggested that the cause of the stereospecific polymerization might be due to the catalyst structure in which LiCl coexists with VCl3, namely, VCl3 ? LiCl or VCl2 ? 2LiCl as a solid solution in the crystalline lattice, since VCl3 prepared by thermal decomposition of VCl4 and a commercial VCl3 did not produce the crystalline polymer and soluble catalysts such as VCl4 in heptane and VCl3 ? LiCl in ether solution did not yield the stereospecific polymer. It was found that some additives, such as tetrahydrofuran or ethylene glycol diphenyl ether, to the catalyst increased the stereospecific polymerization activity of the catalysts. Influence of the polymerization conditions such as temperature, time, monomer and catalyst concentrations, and the kind of solvent on the formed polymer was also examined. 相似文献
Ce0.46Zr0.54O2 solid solution prepared using a cellulose template was employed as a carrier for vanadium catalysts of the oxidative dehydrogenation of propane. The properties of VOх/Ce0.46Zr0.54O2 catalyst (5 wt % vanadium) are compared with the properties of the neat support. The carrier and catalyst are studied by means of BET, SEM, DTA, XRD, and Raman spectroscopy. It is shown that the CeVO4 phase responsible for the ODH process is formed upon interaction between vanadate ions and cerium ions on the surface of the solid solution. The catalytic properties of the catalyst and the support are studied in the propane oxidation reaction at temperatures of 450 and 500°C with pulse feeding of the reagent. It is found that the complete oxidation of propane occurs on the support with formation of CO2 and H2O. Three products (propene, CO2, and H2O) form in the presence of the vanadium catalyst. It is suggested that there are two types of catalytic centers on the catalyst’s surface. It is concluded that the centers responsible for the complete oxidation of propane are concentrated mainly on the carrier, while the centers responsible for propane ODH are on the CeVO4. 相似文献
The partial oxidation of 3- and 4-methylpyridines on V2O5 and vanadium oxide catalysts doped with TiO2, Al2O3, and ZrO2 was studied. The catalytic activities of the studied catalysts were correlated with the calculated proton affinities of the vanadyl oxygen. A possible mechanism of the surface stages of the partial oxidation of 3- and 4-methylpyridines on the vanadium oxide catalysts was discussed. 相似文献
Homopolymerization and copolymerization of trioxane by use of various catalysts have been investigated. When MoO2(AcAc)2 is employed, crystalline homopolymers and copolymers as formed from polymerization exhibit significantly higher melting points than corresponding polymers prepared by use of ordinary cationic catalysts. The higher melting points are attributed to different morphology of the polymer chains formed during polymerization. We now call this phenomenon morphospecific polymerization. This communication describes our results in the copolymerization of trioxane and 1,3-dioxolane and some outstanding properties of the copolymers. A polymerization mechanism is also proposed. 相似文献