共查询到20条相似文献,搜索用时 0 毫秒
1.
2.
3.
Vipin A. Nair Suni M. Mustafa Sreekumar Krishnapillai 《Journal of Polymer Research》2003,10(4):267-273
Divinyl benzene crosslinked polystyrene supported β-diketone linked complexes of Mn(II) have been prepared, characterized
and their role as catalysts in the oxidation of alcohols by Cr(VI) have been studied. The catalytic activity is influenced
by the degree of crosslinking of the polymer matrix, distance between the polymer matrix and metal complex, structural environment
of the ligand and acidity of the medium. A possible mechanism has also been suggested.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
Highly dispersed, multilayered surface metal oxide catalysts (V2O5/MO
x
/SiO2, M = Ti(IV), Zr(IV) or Al(III)) were successfully synthesized by taking into account various factors that govern the maximum dispersion of metal oxide species on silica. The characterization results revealed that the molecular structures of the surface vanadium oxide species on the modified supports are a strong function of environmental conditions. The surface vanadium oxide species under dehydrated conditions are predominantly isolated VO4 units, similar to the dehydrated V2O5/SiO2 catalysts. Upon hydration, the surface vanadium oxide species on the modified supports consist of polymerized VO5/VO6 units and/or less polymerized (VO3)
n
species, which depend on the vanadia content and the specific second metal oxide loading. The surface V cations are found to preferentially interact with the surface metal (Ti, Zr or Al) oxide species on silica. The V(V) cations in the dehydrated state appear to possess both oxygenated ligands of Si(IV)–O– and M–O–. Consequently, the reducibility and catalytic properties of the surface vanadium oxide species are significantly altered. The turnover frequencies of the surface VO4 species on these modified supports for methanol oxidation to redox products (predominantly formaldehyde) increase by more than an order of magnitude relative to the unmodified V2O5/SiO2 catalysts. These reactivity enhancements are associated with the substitution of Si(IV)–O– oxygenated ligands by less electronegative M–O– ligands in the O=V(–O–support)3 structure, which strongly suggests that the bridging V–O–support bonds play a key role in determining the reactivity of the surface vanadium oxide species on oxide supports. 相似文献
5.
6.
In situ Raman spectroscopy at temperatures up to 500°C is used for the first time to identify vanadium species on the surface of a vanadium oxide based supported molten salt catalyst during SO2 oxidation. Vanadia/silica catalysts impregnated with Cs2SO4 were exposed to various SO2/O2/SO3 atmospheres and in situ Raman spectra were obtained and compared to Raman spectra of unsupported model V2O5–Cs2SO4 and V2O5–Cs2S2O7 molten salts. The data indicate that (1) the VV complex VVO2(SO4)2
3– (with characteristic bands at 1034 cm–1 due to (V=O) and 940 cm–1 due to sulfate) and Cs2SO4 dominate the catalyst surface after calcination; (2) upon admission of SO3/O2 the excess sulfate is converted to pyrosulfate and the VV dimer (VVO)2O(SO4)4
4– (with characteristic bands at 1046 cm–1 due to (V=O), 830 cm–1 due to bridging S–O along S–O–V and 770 cm–1 due to V–O–V) is formed and (3) admission of SO2 causes reduction of VV to VIV (with the (V=O) shifting to 1024 cm–1) and to VIV precipitation below 420°C. 相似文献
7.
Several TiO2/SiO2 supports and supported vanadium oxide (vanadia) catalysts of varying titania and vanadia content are synthesized and characterized. Titania rutile phase is not detected for the TiO2/SiO2 supports even up to a calcinations temperature of 1073 K. The supported vanadia catalysts were also studied for the ethane and propane ODH reaction and compared with TiO2 (Degussa P25) supported catalysts. Surface vanadia species are present on the titania or silica part of the TiO2/SiO2 support depending on the titania and vanadia loading of the catalyst. Depending on the vanadia loading in the V2O5/TiO2/SiO2 catalyst the anatase to rutile phase transformation may occur below 1073 K. Furthermore, the ODH activity is retained or decreases less rapidly compared to the TiO2 supported catalyst as the calcination temperature is increased. Consequently, the TiO2/SiO2 supported vanadia catalysts do provide certain advantages compared to the TiO2 (Degussa P25) supported system. 相似文献
8.
Novel vanadium oxide based catalyst derived from the open-framework solid, [Co3V18O42(H2O)12(XO4)]·24 H2O (X = V, S) (1) catalyses oxidative dehydrogenation of propane to propylene. Catalyst activity was evaluated in the temperature range 250–400 °C with varying gas hourly space velocity (GHSV). At 350 °C and GHSV of 9786 h?1 and at 1.3% propane conversion the selectivity to propylene was 36.8%. The major products obtained were propylene and CO x (CO2 and CO). The ratio of the propylene to CO x depended directly on the catalytic sites present. Thus, as the amount of the catalyst was decreased, the conversion decreased with an increase in the propylene selectivity and a decrease in the selectivity to carbon oxides—CO x . The catalyst has been characterized by temperature programmed reduction and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). 相似文献
9.
10.
Catalysis Letters - CeO2, V2O5 and CeVO4 were synthesised as bulk oxides, or deposited over activated carbon, characterized by XRD, HRTEM, CO2-TPO, C3H8-TPR, DRIFTS and Raman techniques and tested... 相似文献
11.
12.
《分离科学与技术》2012,47(16):2591-2605
Abstract Vanadium and arsenic eliminations from an alkaline leaching solution of spent VKCs catalysts were studied. To this end, several commercial resins or polymers synthesized in the laboratory were evaluated in a solid–liquid batch extraction. Conditions for an effective extraction of vanadium and arsenic were determined. An extraction process, using a glass column, is described for the recovery of the vanadium. The elimination of arsenic by precipitation is proposed. 相似文献
13.
Open framework aluminophosphates (AlPOs) with the framework types CHA, AFI, AEI, SAS and SAV have been prepared using nickel complexes of linear and macrocyclic polyamines as structure-directing agents: The [Ni(diethylenetriamine)2]2+ complex has been used to prepare aluminophosphate-fluoride versions of the CHA and AFI topologies as well as substituted metalloaluminophosphates (MAPOs) and silicoaluminophosphates (SAPOs) with the CHA topology; the nickel complex of the macrocycle 1,4,7,10-tetraazacyclododecane (cyclen) acts as a structure-directing agent for MAPO-18 (AEI topology), and the nickel complexes of 1,4,8,11-tetraazacyclotetradecane (cyclam) and 1,4,8,11-tetramethylcyclam direct the formation of STA-6 (SAS topology) or STA-7 (SAV topology) depending on the inorganic composition and the type of amine added as a cobase to control the synthesis pH. Magnesioaluminophosphate-5 (AFI topology) containing complexed nickel has been prepared using a novel mixed azamacrocycle-quinuclidinium cation as a structure-directing agent. Nickel complex-containing AlPOs and SAPOs with the CHA framework topology have been calcined and used as catalysts for the conversion of butane over the temperature range 375 – 575°C with a WHSV of 1.8 h-1. The inclusion of nickel increases the rate of conversion and also changes the composition of the products from the full C1–C4 range to pure methane. This behavior is attributed to the reduction of Ni(II) to finely dispersed supported nickel particles. 相似文献
14.
RebeccaA. Shiels Krishnan Venkatasubbaiah ChristopherW. Jones 《Advanced Synthesis \u0026amp; Catalysis》2008,350(17):2823-2834
Homogeneous tridentate Schiff base vanadium catalysts derived from salicylaldehydes and tert‐leucinol or tert‐leucine are known to be excellent catalysts for the asymmetric oxidation of α‐hydroxy esters including ethyl mandelate. Herein, new analogous supported, semi‐soluble and insoluble catalysts are synthesized and their activities relative to the homogeneous catalyst are reported. The new catalysts are characterized by 1H and 13C NMR spectroscopy, mass spectrometry (EI, ESI, FAB), X‐ray crystallography, elemental analysis, gel permeation chromatography (GPC), Fourier transform infrared (FT‐IR) spectroscopy, and nitrogen physisorption. The effects of support material, synthesis procedure, and reaction solvent are examined to probe the utility of these catalysts. Linear poly(styrene) supported catalysts are partially soluble under the reaction conditions, and it is shown that the soluble species contribute significantly to the catalytic reactivity. Insoluble catalysts based on the same vanadyl complexes supported on cross‐linked poly(styrene) resin or mesoporous silica allow for catalyst recovery and recycle, showing equivalent selectivities over multiple reaction cycles. The mesoporous silica supported catalyst exhibits greater selectivity than the analogous homogeneous and polymer supported catalysts. Rigorous recycle studies show a loss of activity in each recycle, which is attributed to the decomposition of some portion of the vanadyl complexes in each cycle. 相似文献
15.
16.
17.
18.
P. Van Der Voort M. Mathieu E.F. Vansant S.N.R. Rao M.G. White 《Journal of Porous Materials》1998,5(3-4):305-316
Molecular Designed Dispersion (MDD) of metal complexes on a highly porous support is a novel synthesis method to prepare high quality heterogeneous catalysts. The process basically consists of two steps: (1) the anchoring of the complex onto the support in a controlled way and (2) the mild oxidation of the grafted complex towards catalytically active metal-oxide surface structures.This article presents two typical case studies: (1) the incorporation of cationic Cu-complexes in a H-ZSM-5 zeolite from the liquid phase and (2) the gas phase modification of pure silica MCM-48, using the VO(acac)2 complex. In both cases, superior catalysts are obtained. Detailed chemical, physical and catalytical analyses of these catalysts are discussed in the text. Comparison is made with analogous catalysts, prepared by conventional methods. 相似文献
19.