An XPS study of the surface oxidation states of metals in some oxide catalysts

Calcined samples of chromia supported on Al2O3, ZnO, or SnO2 show both Cr(VI) and Cr(III) on the surface, Cr(VI) being preponderant in the case of Al2O3-supported catalysts. The proportion of Cr(VI) decreases with increase in Cr content of the calcined catalysts. Reduction of the supported chromia catalysts in H2 at 720 K for 1 hr gives rise to Cr(III) and Cr(V). On carrying out the dehydrogenation of cyclohexane on the chromia catalysts a higher proportion of Cr(V) is found than after treatment with hydrogen. Vanadia supported on Al2O3 or MoO3 shows significant proportion of V(IV) on carrying out the oxidation of toluene on the catalysts. Calcined MoO3 (10%)/Al2O3 shows only Mo(VI) on the surface at 300 K, but on heating to 670 K in vacuum shows the presence of a considerable proportion of Mo(V) which on cooling disproportionates to Mo(IV) and Mo(VI). Mo(V) is noticed on surfaces of this catalyst on reduction with hydrogen as also on carrying out dehydrogenation of cyclohexane. While Bi2MoO6 shows only Mo(VI) on the surface at 300 K, heating it to 670 K in vacuum changes it entirely to Mo(V) which then gives rise to Mo(IV) and Mo(VI) on cooling.

Kinetics of vapour phase oxidation of furfural on vanadium catalyst

Vapour phase oxidation of furfural over vanadium pentoxide catalyst was studied using an isothermal flow reactor in the temperature range of 220–280°C. Maleic anhydride and carbon dioxide are found to be formed from furfural by a parallel reaction scheme. The following rate equation based on the two-stage redox mechanism—the substance to be oxidized reduces the catalyst which in turn is reoxidized by oxygen from the feed—is found to explain the data satisfactorily. The reoxidation of the reduced catalyst was found to be the rate controlling step.

Oxidation of Thioketens by Singlet Oxygen and Ozone

Di-t-butylthioketen (1) readily reacts with SINGLET-OXYGaEdNdi tion to heterocumulenes is of current singlet oxygen to yield unexpected products (based on interest1 and products derived from the interaction of the behaviour of other heterocumulenes) and reacts with singlet oxygen with the carbon-carbon double bond have ozone to give, quantitatively, the corresponding sul- been characterised. Investigations of the oxidation of phoxide (2). thioketens using di-t-butylthioketen (1) as a model have

Mechanism of vapour phase oxidation of anthracene over cobalt molybdate catalyst

Vapour phase oxidation of anthracene over cobalt molybdate catalyst was investigated in an isothermal flow reactor in the temperature range of 280—340°C. Fifteen different models based on redox, Langmuir—Hinshelwood and Rideal mechanisms were tested in order to elucidate the mechanism of the above reaction. These models were compared on the basis of three criteria and were finally discriminated employing the non-intrinsic parameter method. Two-stage redox mechanism was found to explain the data satisfactorily.

A parametric differentiation version with finite-difference scheme applicable to a class of problems in boundary layer flow with massive blowing

A numerical procedure, based on the parametric differentiation and implicit finite difference scheme, has been developed for a class of problems in the boundary-layer theory for saddle-point regions. Here, the results are presented for the case of a three-dimensional stagnation-point flow with massive blowing. The method compares very well with other methods for particular cases (zero or small mass blowing). Results emphasize that the present numerical procedure is well suited for the solution of saddle-point flows with massive blowing, which could not be solved by other methods.

Separation β-apocarotenals and related compounds by reversed-phase paper and thin-layer chromatography

Abstract is not available.

Dual Drug Delivery Microcapsules via Layer-by-Layer Self-Assembly

The integration of hydrophobic and hydrophilic drugs in the polymer microcapsule offers the possibility of developing a new drug delivery system that combines the best features of these two distinct classes of material. Recently, we have reported the encapsulation of an uncharged water-insoluble drug in the polymer membrane. The hydrophobic drug is deposited using a layer-by-layer (LbL) technique, which is based on the sequential adsorption of oppositely charged polyelectrolytes onto a charged substrate. In this paper, we report the encapsulation of two different drugs, which are invariably different in structure and in their solubility in water. We have characterized these dual drug vehicular capsules by confocal laser scanning microscopy, atomic force microscopy, visible microscopy, and transmission electron microscopy. The growth of a thin film on a flat substrate by LbL was monitored by UV−vis spectra. The desorption kinetics of two drugs from the thin film was modeled by a second-order rate model.

Boundary-layer flows with swirl and large suction

An analytical solution is presented for the laminar swirling flow in a tube. Attention is given to a particular type of swirling flow corresponding to a zero longitudinal acceleration parameter, with large suction at the surface. The investigation shows that in the case of very large rates of suction the velocity overshoot can be almost eliminated. This is even possible in flows with swirls which are characterized by a velocity overshoot in the longitudinal direction.

Vanadate stimulates oxidation of NADH to generate hydrogen peroxide

Vanadate in the polymeric form of decavanadate, but not other forms, stimulated oxidation of NADH to NAD+ NADPH was also oxidized with comparable rates. This oxidation of NADH was accompanied by uptake of oxygen and generated hydrogen peroxide with the following stoichiometry: NADH + H+ + O2 → NAD+ + H2O2. The reaction followed second-order kinetics. The rate was dependent on the concentration of both NADH and vanadate and increased with decreasing pH. The reaction had an obligatory requirement for phosphate ions. Esr studies in the presence of the spin trap dimethyl pyrroline N oxide indicated the involvement of Superoxide anion as an intermediate. The reaction was sensitive to Superoxide dismutase and other scavengers of superoxide anions.

Catalyzed air oxidation for treatment of thiosalt effulents

Continuous slurry reactor runs of two to four weeks duration were carried out for catalyzed air oxidation of thiosalts under a variety of conditions using poly (4-vinylpyridine) - Cu (II) and quaternized poly (4-vinylpyridine) - Cu (II) catalysts. Results obtained indicate that these catalysts have high activity and relatively long-term catalyst stability for thiosalt waste streams of < 1000 ppm thiosalt level. Using 2% (w/w) slurries of the poly (4-vinylpyridine) Cu (II) catalyst, effective oxidation of 700 ppm S2O32− influent to an effluent of < 100 ppm total thio-salts can be carried out continuously for at least one month when operating at 20 to 30°C with solution flow rates of$˜1l/h and aeration of 1300 XXX/h using a two-stage reactor system comprised of 12 l reactors. At higher thiosalt influent levels (i.e. > 1600 ppm) increased reaction temperatures enable depletion to < 100 ppm thiosalt effluent levels for up to one week of continuous operation. The catalysts deactivate much more readily at these higher influent levels as a result of greater copper losses and appreciable adsorption of S2O32− and S4O62−. The behaviour of continuous slurry reactors employed in the experimental studies, by use of batch reaction data for the poly (4-vinylpyridine) Cu (II) catalyzed oxidation of thiosalts, can be modelled successfully. Quaternized poly (4-vinylpyridine) Cu (II) catalyst has good long-term stability and copper losses are very low. The poly (4-vinylpyridine) Cu (II) catalyst, however, is susceptible to appreciable oxidation of the polymer matrix on long-term usage. This oxidation of the polymer matrix results in a substantial loss in the activity of the regenerated catalyst.

Mechanics of transition in an axisymmetric laminar boundary layer on a circular cylinder

Measurements of the growth of artificially generated turbulent spots and intermittency distribution in the transition region on a circular cylinder in axial flow show that the instability Reynolds number of 11,000 has a marked effect on the properties. In particular, it is found that the spot production in the initial region when a single turbulent spot has not yet wrapped around the cylinder and the propagation is essentially two-dimensional, is significantly altered. But the transition in the downstream or latter region, where most of the turbulent spots propagate onedimensionally (like the turbulent plugs in a pipe), is not affected. When the radius Reynolds number is more than 11,000, the intermittency law in the initial region is essentially the same as in twodimensional flow on a flat plate and in the latter region it is the one-dimensional flow in a pipe, the demarcation between the two regions being quite sharp.

Mechanistic investigations into the photochemical oxidation of thioketones

Singlet-oxygen reaction with dialkyl, aryl alkyl, and diaryl thioketones is found to give the corresponding sulphines and ketones in proportions depending on the nature of the thioketone.

Similar solutions for the incompressible laminar boundary layer with pressure gradient in micropolar

This paper presents the similarity solution for the steady incompressible laminar boundary layer flow of a micropolar fluid past an infinite wedge. The governing equations have been solved numerically using fourth orderRunge-Kutta-Gill method. The results indicate the extent to which the velocity and microrotation profiles, and the surface shear stress are influenced by coupling, microrotation, and pressure gradient parameters. The important role played by the standard length of the micropolar fluid in determining the structure of the boundary layer has also been discussed.

Investigations on the preparation, oxidation and reduction reactions of thiophosphoryl fluoride

Pure thiophosphoryl fluoride has been prepared by the fluorination of thiophosphoryl chloride by sodium fluoride in acetonitrile medium. Oxidation of this phosphoryl fluoride by acidified chloramine-T ruptures the phosphorus-sulphur bond and oxidises the sulphur present to the hexavalent state. Anhydrous hydrogen iodide reduces the sulphur to hydrogen sulphide and phosphorus to the trivalent state.

Oxidase-peroxidase enzymes of Datura innoxia. Oxidation of formylphenylacetic acid ethyl ester

An enzyme system from Datura innoxia roots oxidizing formylphenylacetic acid ethyl ester was purified 38-fold by conventional methods such as (NH4)2SO4 fractionation, negative adsorption on alumina Cy gel and chromatography on DEAE-cellulose. The purified enzyme was shown to catalyse the stoicheiometric oxidation of formylphenylacetic acid ethyl ester to benzoylformic acid ethyl ester and formic acid, utilizing molecular O2. Substrate analogues such as phenylacetaldehyde and phenylpyruvate were oxidized at a very low rate, and formylphenylacetonitrile was an inhilating agents, cyanide, thiol compounds and ascorbic acid. This enzyme was identical with an oxidase-peroxidase isoenzyme. Another oxidase-peroxidase isoenzyme which separated on DEAE-chromatography also showed formylphenylacetic acid ethyl ester oxidase activity, albeit to a lesser extent. The properties of the two isoenzymes of the oxidase were compared and shown to differ in their oxidation and peroxidation properties. The oxidation of formylphenylacetic acid ethyl ester was also catalysed by horseradish peroxidase. The Datura isoenzymes exhibited typical haemoprotein spectra. The oxidation of formylphenylacetic acid ethyl ester was different from other peroxidase-catalysed reactions in not being activated by either Mn2+ or monophenols. The oxidation was inhibited by several mono- and poly-phenols and by catalase. A reaction mechanism for the oxidation is proposed.