Kinetic conversion of complex hydrocarbon mixtures in reforming on platinum/alumina catalysts

General forms of the kinetic equations for the conversion of various hydrocarbons in reforming of multicomponent gasoline fractions on platinum/alumina catalysts have been confirmed experimentally by using a gradientless method.

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Structural thermal and textural studies on cobalt oxide/alumina supported catalysts

CoO/Al₂O₃ catalysts containing amounts of cobalt ranging form 2 to 20% were prepared atpH 11 from neutral mesoporous alumina composed of γ-Al₂O₃ and poorly crystalline boehmite, and were then dried at 80?C. X-ray diffraction, DTA and TG techniques were used to study the structural changes produced upon thermal treatment up to 700?C. Soaking of the alumina in cobalt ammine complex solutions for a period of 10 days (the time required for equilibrium) resulted in a series of catalyst samples (I–V). Another sample (III-a) was soaked for a period of 5 days only in order to study the effect of the soaking time upon the equilibrium conditions. Cobalt aluminate (CoAl₂O₄) bands were characterized in all catalyst samples except III-a. They increased in intensity with increasing cobalt content. Surface species appeared in samples heated to 80?C, and others persisted at 150?C. Heating to temperatures above 200?C resulted in the formation of cobalt oxides, due to decomposition of the surface compounds. DTA and TG studies showed that this was more pronounced at higher concentrations of cobalt. Samples heated at 500?C and above did not undergo any further structural changes, except that the boehmite in the support was converted to γ-Al₂O₃. The variations in the surface parameters followed the same pattern as found previously [1], demonstrating that the catalyst samples are mesoporous, with retention of two ranges of pore size in most cases.     

Oxidation of 4-methoxy-1-naphthol on promoted platinum catalysts

Oxidative coupling of naphthols is a useful method for the formation of new carbon-carbon bonds in organic synthesis. In the presence of hydrogen peroxide, platinum supported on activated carbon catalyses this reaction. The outcome is influenced by the solvent, the reaction temperature and the physical structure of the catalyst. The catalyst structure is determined by the synthesis method and the modifier used (Bi or Sb). Within 40 min 4-methoxy-1-naphthol can be converted to 4,4'-dimethoxy-2,2'-binaphthalenyl-1,1'-diol with a yield of up to 94%, or to 4,4'-dimethoxy-2,2'-binaphthalenylidene-1,1'-dione with a yield of 92%. High amounts of quinoid byproducts (≤22%) are observed in nitromethane as the solvent.     

Thermal characterisation of alumina supported chromium and platinum–chromium catalysts

This study presented results on reduction of alumina supported chromium and platinum–chromium catalysts using temperature programmed reduction method (TPR). It has been shown that catalysts after earlier oxidation step but without calcinations one undergo reduction in lower temperature in comparison to calcined only catalysts. Moreover, addition platinum to Cr/Al₂O₃ catalysts also caused decrease of reduction temperature. It has been observed that over the examined catalysts oxidation CO to CO₂ and reduction CO to CH₄ occurs. However, on Pt–Cr catalysts both reactions proceed at lower temperature compare to Cr catalysts.     

Adsorption of nitrous oxide on metallic copper catalysts

With the help of UPS spectroscopy, it has been shown that N₂O decomposes into N₂ and surface Cu₂O over copper catalysts in the temperature range –150, –100°C. The surface oxide oxygen dissolved into the bulk above 100°C to some extent.

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, N₂O –150° –100°C, N₂ Cu₂O. 100°C.

     

Oxidation of n-propanol over vanadium oxide catalysts

The kinetics of catalytic oxidation of n-propanol on V₂O₅ and V₂O₅ modified with BeO, MgO, CaO and SrO has been investigated. A high selectivity of the oxidation to propionaldehyde was observed. The activation energies of the reaction and of the exchange of oxygen in these catalysts with molecular oxygen and CO₂ were found to change in parallel.

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- V₂O₅ V₂O₅ BeO, CaO, MgO SrO. . .

     

Characterization and catalytic functionalities of copper oxide catalysts supported on zirconia

A series of zirconia supported copper oxide catalysts with varying copper loadings (1.2-19.1 wt %) were prepared by impregnation method. The catalysts were characterized by X-ray diffraction, UV-visible diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), and temperature-programmed desorption of CO2. Copper dispersion and metal area were determined by N2O decomposition method. X-ray diffraction patterns indicate the presence of crystalline CuO phase beyond 2.7 wt % of Cu on zirconia. UV-visible diffuse reflectance spectra suggest the presence of two types of copper species on the ZrO2 support. XPS peaks intensity ratio of Cu 2p3/2 and Zr 3d5/2 was compared with Cu dispersion calculated from N2O decomposition. TPR patterns reveal the presence of highly dispersed copper oxide at lower temperatures and bulk CuO at higher temperatures. The basicity of the catalysts was found to increase with Cu loading, and the activity of the catalysts was also found to increase with the increase in Cu loading up to 2.7 wt % Cu loading. The catalytic properties were evaluated for the dehydrogenation of cyclohexanol to cyclohexanone and were related to surface properties of the copper species supported on zirconia.     

Mechanism of hydrogenation of nitric oxide on platinum catalysts in acidic solution

To explain the mechanism of hydrogenation of NO in 2 M H₂SO₄, the kinetics of the hydrogenation of hydroxylamine to ammonia were studied. The rate constant of this reaction was compared with the ratio of rates at which NH₃OH⁺ and NH ₄ ⁺ were generated by the hydrogenation of NO. Both of these products are formed from NO via parallel reactions of a common intermediate. A mechanism for the hydrogenation of NO and the shift of the catalyst of the potential is proposed.

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NO 2M H₂SO₄ . NH₃OH⁺ NH₄ ⁺ NO. NO . . ., NO .

     

Kinetics of n-hexadecane hydrocracking on nickelmolybdenum/alumina catalysts

Composition of the products of n-hexadecane hydrocracking on Ni–Mb–Al catalysts has been determined. It is shown that the data of a single experiment can be used to obtain four rate constants for hydroisomerization and hydrocracking of n-hexadecane and its isomers.

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Oxidation of 3- and 4-methylpyridines on modified vanadium oxide catalysts

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.     

Catalytic dehydration of ethanol using transition metal oxide catalysts

The aim of this work is to study catalytic ethanol dehydration using different prepared catalysts, which include Fe(2)O(3), Mn(2)O(3), and calcined physical mixtures of both ferric and manganese oxides with alumina and/or silica gel. The physicochemical properties of these catalysts were investigated via X-ray powder diffraction (XRD), acidity measurement, and nitrogen adsorption-desorption at -196 degrees C. The catalytic activities of such catalysts were tested through conversion of ethanol at 200-500 degrees C using a catalytic flow system operated under atmospheric pressure. The results obtained indicated that the dehydration reaction on the catalyst relies on surface acidity, whereas the ethylene production selectivity depends on the catalyst chemical constituents.     

Oxidation of ethanol on platinum nanoparticles: surface structure and aggregation effects in alkaline medium

Journal of Solid State Electrochemistry - The ethanol oxidation reaction in 0.1 M NaOH on Pt nanoparticles with different shapes and loadings was investigated using electrochemical and...     

Effect of potassium on alumina supported chromium oxide catalysts for methylene chloride oxidation

Alumina supported chromium oxide catalysts added potassium were prepared and tested for methylene chloride oxidation. They were investigated by XRD, BET, XPS, chemisorption. Chromium oxide catalyst added potassium of 1 wt.% has a large beneficial effect on activity. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of cerium oxide on the activity of platinum catalysts of hydrogen and CO oxidation

Effective catalytic systems based on Pt/CeO₂-C were prepared. The use of a cerium oxide addition in the substrate stabilized the platinum catalysts against their poisoning with carbon monoxide at room temperature.     

Photo- and radiation-induced preparation of nanocrystalline copper and cuprous oxide catalysts

Spherical copper nanoparticles have been prepared by photo- or radiation-induced reduction of aqueous solutions containing 10⁻³ mol.dm⁻³ copper sulphate or formate, 1.3 mol.dm⁻³ propan-2-ol and polyvinyl alcohol as a stabilizer. Increase of initial copper concentration to 10⁻² mol.dm⁻³ resulted in formation of different reaction product—octahedral cuprous oxide nanoparticles. Solutions were irradiated by means of electron beam, ⁶⁰Co γ rays (dose rate 70 Gy.h⁻¹) or by 400 W medium-pressure mercury lamp and were characterised by UV-Vis spectrophotometry, X-Ray Powder Diffraction, TEM and SEM. Pink to violet colour of colloidal copper solutions corresponded to measured copper surface plasmon band at circa 580 nm and has been found to be very sensitive to oxygen, which causes dissolution of particles. Therefore, the influence of purging by nitrogen gas prior to irradiation was thoroughly examined and has been found to only hinder, not alter irradiation effects. Moreover, the evolution of absorption spectrum of colloidal copper solution in contact with air has been measured, revealing interesting non-monotonous dependence on the air exposure time, probably caused by formation of protective oxide layer. Catalytic activity of prepared cuprous oxide has been measured by catalytic decomposition of hydrogen peroxide and has been found to be higher or comparable to commercial cuprous oxide.     

Selective oxidation of hydrogen sulfide over potassium promoted vanadium oxide on a alumina catalysts

The effect of potassium addition to alumina supported vanadium catalysts on the catalytic activity for the selective oxidation of H₂S is investigated. XRD, XPS and XANES have been used to characterize a series of K-V/Al₂O₃catalysts. The enhanced sulphur yield has been correlated with the crystallinity of vanadium. This revised version was published online in August 2006 with corrections to the Cover Date.     

Characterization and reactivity of copper oxide catalysts supported on TiO2-ZrO2

A series of copper catalysts supported on TiO2-ZrO2 with copper loading varying from 1.0 to 21.6 wt % were prepared by a wet impregnation method. The catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy, electron spin resonance (ESR), temperature programmed reduction (TPR), and Brunauer-Emmett-Teller specific surface area measurements. Copper dispersion and metal area were determined by N2O decomposition by the passivation method. XRD results suggest that the copper oxide is present in a highly dispersed amorphous state at copper loadings <16.8 wt % in the sample and as a crystalline CuO phase at higher Cu loadings. Copper dispersion increases with Cu loading up to 5.1 wt % and levels off at higher loadings. The XPS peak intensity ratios of Cu 2p(3/2)/Ti 2p(3/2) and Cu 2p(3/2)/Zr 3d(5/2) were compared with the copper dispersion calculated from N2O decomposition. ESR results suggest the presence of two types of copper species on the TiO2-ZrO2 support. TPR profiles reveal the presence of highly dispersed copper oxide at lower temperatures and bulk CuO at higher temperatures. The catalytic properties were evaluated for the vapor-phase dehydrogenation of cyclohexanol to cyclohexanone and related to the dispersion of Cu on TiO2-ZrO2.