Search results for "ALK"
showing 10 items of 4314 documents
Group contributions to the infinite dilution partial molar volumes of alkanes, alcohols, and glycols in polar organic solvents
1997
Densities of binary mixtures of polar organic solvents with alcohols were measured at 25‡C. The solvents studied were N,N-dimethylformamide, dimethylsulfoxide, and formamide while alcohols were butanol, pentanol, hexanol, and 1,4-butanediol. Density measurements of hydrocarbons (from pentane to dodecane and some heptane isomers) + N,N-dimethylformamide were also performed. From these data the apparent molar volumes of alcohols and hydrocarbons as functions of concentration were calculated. The standard partial molar volumes were obtained by extrapolation to infinite dilution and are discussed in terms of group contributions.
On the influence of the acid-base character of catalysts on the oxidative dehydrogenation of alkanes
1996
Vanadium oxides supported on metal oxide, i.e. Al2O3, MgO and Mg-Al mixed oxide, and V-containing microporous materials (VAPO-5 and MgVAPO-5) have been tested in the oxidative dehydrogenation of C2-C4 alkanes. In all cases, tetrahedral vanadium species (isolated and/or associated) were mainly observed from51V-NMR and diffuse reflectance spectroscopies. The reducibility of V5+-species, determined from the onset-reduction temperature, decreases as follows: VOx/AL > VAPO-5 > MgVAPO-5 =VOx/MG > VOx/MG + AL. The acid character of catalysts, determined from the FTIR spectra of pyridine adsorbed, decreases as: MgVAPO-5 > VOx/AL > VAPO-5 > VOx/MG + AL > VOx/MG. A similar trend between V-reducibilit…
Monolayers of asymmetrical diethylalkanoat disulfides on gold(111):.the influence of chain length difference on atomic force microscope images
1998
Several symmetrical and asymmetrical long-chain diethylalkanoat disulfides were synthesized and character- ized. The differences in the chain lengths of the disul- fides ranged between zero and five methylene units. Self- assembled monolayers of these disulfides formed on Au(111) surfaces were studied by atomic force microscopy (AFM) in order to obtain information about the origin of the image contrast. Domains with hexagonal lattices (lattice constants 5:2- 5:3 A) were detected for all derivatives, independent of the chain length differences. This indicates that the contrast arises roughly at a depth of 4- 8 A in the monolayers at imag- ing forces between 0: 2a nd 3n N. For SAMs of diethyl…
Reaction products and pathways in the selective oxidation of C-2-C-4 alkanes on MoVTeNb mixed oxide catalysts
2010
[EN] The catalytic properties of MoVTeNbO catalysts during the selective oxidation of short chain alkanes and olefins (C-2-C-4) have been comparatively studied The main reaction products have been ethylene from ethane acrylic acid from propane maim anhydride from n-butane and methacrolein from isobutane FTIR studies of the adsorption of the main reaction products i e olefins and aldehydes over MoVTeNbO catalyst has been carried out Accordingly the reaction pathway is explained on the basis of the characteristics of the alkane fed the stability and reactivity of both the intermediates and the reaction products and the nature of the catalytic sites involved in each reaction (C) 2010 Elsevier …
Nonporous Organic Solids Capable of Dynamically Resolving Mixtures of Diiodoperfluoroalkanes
2009
Halogen bonding has increasingly facilitated the assembly of diverse host-guest solids. Here, we show that a well-known class of organic salts, bis(trimethylammonium) alkane diiodides, can reversibly encapsulate α,ω-diiodoperfluoroalkanes (DIPFAs) through intermolecular interactions between the host's I – anions and the guest's terminal iodine substituents. The process is highly selective for the fluorocarbon that forms an I – ···I(CF 2 ) m I···I – superanion that is matched in length to the chosen dication. DIPFAs that are 2 to 12 carbons in length (common industrial intermediates) can thereby be isolated from mixtures by means of crystallization from solution upon addition of the dissolv…
Catalytic cracking of n-alkane naphtha: The impact of olefin addition and active sites differentiation
2015
An extended dual kinetic model allows to fit the n-heptane cracking results working in a wide range of reaction conditions. The duality of the model is provided by the contribution of monomolecular and bimolecular cracking mechanisms. It takes into account the role played by the olefins formed on the global cracking or added within the feed. Furthermore by means of this model and the kinetic parameters obtained when cracking n-heptane on ZSM-5, it has been observed that, while some characterization techniques show a homogeneous zeolite surface from the point of view of the active sites, rigorous kinetic experiments point to the possibility that the reactant sees a heterogeneous surface with…
On the effect of pressure on the phase transition of polymer blends and polymer solutions: Oligostyrene–n-alkane systems
2001
Critical temperatures of some binary solutions of weakly interacting low molecular weight polystyrenes dissolved in linear alkanes (oligoethylenes) were measured over the range 0.1 to 100 MPa. While (dT/dP)crit along the upper critical solution (UCS) locus for a “typical blend” is positive, and for the “ typical solution” can be either positive or negative (but is usually negative), there is no essential difference between blend and solution. Rather, the difference in sign is a consequence of the location of the hypercritical point (that point in (T,P)crit space where (dT/dP)crit changes sign, [(dT/dP)crit = 0 and (d2T/dP2)crit>0], also called the double critical point, DCP), which is norma…
Organo-catalyzed synthesis of aliphatic polycarbonates in solvent-free conditions
2012
A new efficient and expeditious route to the synthesis of aliphatic polycarbonates, in solvent-free conditions and using 1-n-butyl-3-methylimidazolium-2-carboxylate (BMIM-2-CO2) as a catalyst precursor, is described. The protocol consists of a two-step polymerization process involving the transesterification of dimethyl carbonate (DMC) with linear alkane diols and leading to high molecular weight homopolymers. The reaction went to completion quantitatively with the liberation of methanol as the only by-product. The in situ formation of N-heterocyclic carbene species resulting from BMIM-2-CO2 decarboxylation is suggested to be a key feature of the condensation process. The protocol was then …
Deep oxidation of volatile organic compounds using ordered cobalt oxides prepared by a nanocasting route
2010
Ordered Co3O4 with high surface area (until 173 m2/g) has been successfully obtained through a nanocasting route using mesoporous KIT-6 silica as a hard template and tested in the deep oxidation of a series of representative volatile organic compounds (VOCs): propane as a model of short chain alkane and toluene as a model of monoaromatic hydrocarbon. It has been demonstrated that the catalytic activity for VOC deep oxidation is very elevated and its catalytic stability at moderate temperatures very good. However, the role of the ordered structure in the catalytic performance does not seem to be beneficial. The enhanced catalytic activity has been explained in terms of both the high surface …
Theoretical characterization of iron and manganese porphyrins for catalyzed saturated alkane hydroxylations
1997
Abstract The theoretical characterization of porphin (H2Por), iron and manganese porphyrins MIII(Por) and their chlorine derivatives MIII(Por)Cl has been carried out. This work represents a first step for modelling catalyzed saturated alkane hydroxylations. The chlorine atom is responsible for the existence of a dipole moment of 1.2–2.0 D in the MIII(Por)Cl molecules and for a negative value of the mean quadrupole moment (−16–(−14)DA). The charge of the metal atom (1.8–2.2 e) is rather varied (to 2.1–2.6 e) and the effective polarizability (2.8–2.9 A3) is increased (to 3.5–3.6 A3) by the addition of the chlorine atom. Starting from the porphin molecule, the presence of the metal atom decrea…