Javier M. Grau

Conversion of heavy n-alkanes into light isomers over H-mordenite, platinum/H-mordenite, platinum/alumina and composite catalysts

Abstract H-MOR, chlorided Al2O3, Pt/H-MOR, Pt/Al2O3, Pt-Re/Al2O3 and some of their mixtures were used as catalysts in the isomerization-cracking of pure n-alkanes (n-C7 to n-C12) and two paraffinic commercial cuts at 1.5 MPa, 473–773 K, H2:n-alkane = 6 and weight hourly space velocity = 4. Depending on the degree of conversion, the sequence of reactions on all catalysts was: isomerization, central and successive cracking. The activity and selectivity to light isomere increase with the increase in platinum concentration using Pt/H-MOR. The conversion increases with the chain length of the n-alkane, presenting an optimum temperature at which light isomers production is maximum. Ratios isoalkane/n-alkane higher than those corresponding to thermodynamic equilibrium are obtained. H-MOR is deactivated due to the production of a large amount of coke, which greatly decreases the specific surface area and pore volume of the zeolite. The synergy produced by the addition of platinum decreases deactivation and increases the selectivity to isoalkanes. A composite catalyst obtained by pressing powders of H-MOR and Pt/Al2O3 (platinum is in this case outside the zeolite particle) showed the best synergetic effect, which depends on the contact of the particles and which is ascribed to hydrogen spillover from platinum to H-MOR. This spillover decreases coke formation on and blocking of the surface of H-MOR.

Single and composite bifunctional catalysts of H-MOR or SO42−ZrO2 for n-octane hydroisomerization-cracking. Influence of the porosity of the acid component

Abstract The performances of two materials with different acidic and textural properties, H-Mordenite and SO 4 2− ZrO 2 , are compared in the hydroisomerization-cracking of n -octane at 573 K and 1.5 MPa, aiming at the production of light isomers. To obtain a bifunctional catalyst, a metallic function (Pt or Pd) is added either to the acid material or in a composite catalyst prepared by mixing the acid materials with either metal/SiO 2 or metal/Al 2 O 3 . The synergy of functions produces catalysts more selective to isomers. Since the deactivation by pore blockage decreases, the composite catalysts with H-Mordenite present an improved stability. The composite catalysts with SO 4 2− ZrO 2 do not present this improvement because of their wide pore size distribution.

Cadmium removal from aqueous sulphate solutions by treatment with iron felts

The possibility of removing cadmium from effluents byelectrochemical treatment using iron felts as three-dimensional electrodes was investigated. It was found that iron felts remove cadmium by three paths: (i) adsorption of cadmium ions by hydrous ferric oxide, (ii) cathodic electrodeposition and (iii) precipitation of cadmium hydroxide due to the localized alkalinity produced by the hydrogen evolution. The adsorption isotherm, at 30°C, of cadmium ions from an aqueous sulphate solution on hydrous ferric oxide is given. The influence of cathodic potential, volumetric flow rate and interelectrode gap on the current, current efficiency and fractional conversion is discussed. The iron felts proved to be efficient in removing cadmium. The highest fractional conversion, ≌25% for single pass operation, with 100% current efficiency was obtained for a volumetric flow rate of 9·57×10−6 m3 s−1 using iron felt cathodes of 4×10−3 m thickness potentiostated at potentials lower than −1·5 V against a saturated calomel electrode.

The burning of coke on Pt-Re/Al2O3

Abstract In order to follow coke burning on a Pt-Re/Al2O3 catalyst commercially coked, several experiments in a bench scale equipment with an isothermically-operated reactor were made. The influence of the operating temperature, pressure, and flow rate on CO2 concentration in the outlet gas was studied. Comparing the results and photographs of the radial coke distribution during the burning, a model stating the presence of several types of coke with different degrees of polymerization was proposed. Experiments in a Differential Thermal Analysis equipment were carried out in order to determine operating conditions under which the ignition of coke burning reactions takes place. It was found that the exothermicity of combustion of the hydrogen adsorbed on the metal is important in initiating the coke burn-off.

Pt-Co and Pt-Ni Catalysts of Low Metal Content for H2 Production by Reforming of Oxygenated Hydrocarbons and Comparison with Reported Pt-Based Catalysts

New catalysts of Pt, PtNi, PtCo, and NiCo supported on Al2O3 were developed for producing hydrogen by aqueous phase reforming (APR) of oxygenated hydrocarbons. The urea matrix combustion technique was used for loading the metal on the support in order to improve several aspects: increase both the metal-support interaction and the metal dispersion and decrease the metal load. The catalysts were characterized by MS/ICP, N2 adsorption, XRD, TPR, CO chemisorption, and the test of cyclohexane dehydrogenation (CHD). The APR of a solution of 10% mass ethylene glycol (EG), performed in a tubular fixed bed reactor at 498 K, 22 bar, WHSV = 2.3 h−1, was used as the main reaction test. After 10 h on-stream, the catalysts prepared by UMC had better hydrogen yield and catalytic stability than common catalysts prepared by IWI. The UMC/IWI H2 yield ratio was 23.5/15.2 for Pt, 24.0/17.0 for PtCo, 26.6/21.0 for PtNi, and 8.0/3.9 for NiCo. Ni or Co addition to Pt increased the carbon conversion while keeping the H2 turnover high. Cobalt also improves stability. Reports of several authors were revised for a comparison. The analysis indicated that the developed catalysts are a viable and cheaper alternative for H2 production from a renewable resource.