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.

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.

Exact analysis of simply supported rhombic plates under uniform pressure

The simply supported rhombic plate under transverse load has received extensive attention from elasticians, applied mathematicians and engineers. All known solutions are based on approximate procedures. Now, an exact solution in a fast converging explicit series form is derived for this problem, by applying Stevenson's tentative approach with complex variables. Numerical values for the central deflexion and moments are obtained for various corner angles. The present solution provides a basis for assessing the accuracy of approximate methods for analysing problems of skew plates or domains.

Photoimpedance characterization of polymer field-effect transistor

The small signal ac response is measured across the source-drain terminals of poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) field-effect transistor under dc bias to obtain the equivalent circuit parameters in the dark, and under a monochromatic light (540 nm) of various intensities. The numerically simulated response based on these parameters shows deviation at low frequency which is related to the charge accumulation at the interface and the contact resistance at the electrodes. This method can be used to differentiate the photophysical phenomena occurring in the bulk from that at the metal-semiconductor interface for polymer field-effect transistors. ©2009 American Institute of Physics

Natural frequencies of circumferentially truncated sector plates with simply supported straight edges

The classical Rayleigh-Ritz method in conjunction with suitable co-ordinate transformations is found to be effective for accurate estimation of natural frequencies of circumferentially truncated circular sector plates with simply supported straight edges. Numerical results are obtained for all the nine combinations of clamped, simply supported and free boundary conditions at the circular edges and presented in the form of graphs. The analysis confirms an earlier observation that the plate behaves like a long rectangular strip as the width of the plate in the radial direction becomes small.

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.

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.

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.

Three-component assembly of a metal-inorganic 3D Co(II) polymer containing bridging hydrazine

Three-component metal-inorganic assembly of a Co(II) network representing the first example of a 3D coordination polymer containing a hydrazine bridging ligand, has been synthesized and characterized.

Catalyst effectiveness factor for redox model kinetic equation

A generalized isothermal effectiveness factor correlation has been proposed for catalytic reactions whose intrinsic kinetics are based on the redox model. In this correlation which is exact for asymptotic values of the Thiele parameter the effect of the parameters appearing in the model, the order of the reaction and particle geometry are incorporated in a modified form of Thiele parameter. The relationship takes the usual form: Image and predicts effectiveness factor with an error of less than 2% in a range of Thiele parameter that accommodates both the kinetic and diffusion control regimes.

Natural frequencies of circumferentially truncated sector plates with simply supported straight edges

The classical Rayleigh-Ritz method in conjunction with suitable co-ordinate transformations is found to be effective for accurate estimation of natural frequencies of circumferentially truncated circular sector plates with simply supported straight edges. Numerical results are obtained for all the nine combinations of clamped, simply supported and free boundary conditions at the circular edges and presented in the form of graphs. The analysis confirms an earlier observation that the plate behaves like a long rectangular strip as the width of the plate in the radial direction becomes small.

Homogeneous hydrogenations ofα, β-unsaturated compounds using pentacyanocobaltate (II) anion as catalyst system

Hydrogenation of someα, β-unsaturated carbonyl compounds using potassium pentacyanocobaltate (II), K3Co(CN)5, as a homogeneous catalyst has been investigated. Thus, hydrogenation of 1-carvone (I), mesityl oxide (4), 2-cyclohexenone (8) and benzalacetone (6) afforded the corresponding dihydrocompounds. Hydrogenation ofβ-ionone (10) afforded a mixture of theα, β-dihydrocompounds (14) and (15). In all these cases, it was observed that the reaction proceeded to completion only in the presence of added base. Hydrogenation of 5α-androst-l-en-17β-ol-3-one acetate (19) afforded the saturated compound, 5α-androst-17β-ol-3-one (20) in 60% yield. It was found that other steroid enones and dienones were not reduced by this catalyst system.

Mechanical properties of nanodiamond-reinforced polymer-matrix composites

Poly(vinyl alcohol)-matrix reinforced with nanodiamond (ND) particles, with ND content up to 0.6 wt%, were synthesized. Characterization of the composites by transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS) reveal uniform distribution of the ND particles with no agglomeration in the matrix. Differential scanning calorimetry reveals that the crystallinity of the polymer increases with increasing ND content, indicating a strong interaction between ND and PVA. Nano-indentation technique was employed to assess the mechanical properties of composites. Results show that even small additions of ND lead to significant enhancement in the hardness and elastic modulus of PVA. Possible micromechanisms responsible for the enhancement of the mechanical properties are discussed.