Juan de Dios López-González

Platinum catalysts supported on activated carbons: II. Isomerization and hydrogenolysis of n-butane

Abstract A series of carbon-supported Pt catalysts prepared using different precursors and methods and covering a wide range of metal dispersion (8–51) have been studied in the reaction of n-butane with hydrogen. These are basically hydrogenolysis catalysts in which the splitting of the terminal CC bond predominates. The hydrogenolysis of n-butane is a reaction sensitive to the structure of the catalysts, whereas this is not the case for isomerization. The selectivity for hydrogenolysis increases with decreasing mean Pt particle size. The apparent activation energies for the two reactions (larger for isomerization) are independent of particle size.

Hydrogenation of CO on carbon-supported iron catalysts prepared from iron penta-carbonyl

Abstract Fe catalysts supported on an activated carbon were prepared using Fe(CO)5 as the precursor and subsequently reduced in a flow of hydrogen at different temperatures to induce various degrees of particle sintering. The catalysts were used in the hydrogenation of CO and it was found that the specific activity decreases with decreasing iron metal particle size; however, the large olefin to alkane ratios are maintained even for large metal particles. The effect of both the CO to H2 ratio of the reactants on-stream and the reaction time on the specific activity, the selectivity toward hydrocarbons and the distribution of products was also studied.

The effect of inorganic constituents of the support on the characteristics of carbon-supported platinum catalysts

Abstract Two commercial activated carbons and the corresponding demineralized samples have been used as catalyst supports for platinum, in order to learn about the role played by the inorganic constituents of the carbons on the catalyst characteristics. CO and H2 chemisorption and X-ray line broadening have been used to determine metal dispersion and mean particle size. The results indicate that the inorganic matter of the carbon plays an important role in the stabilization of the average platinum particle size by making sintering more difficult. H2-C2H4 titrations have also been used to determine the platinum particle size; the results found are in good agreement with H2 chemisorption, especially for catalysts supported on carbons with larger micropore volume and lower meso and macropore volume.

Reactivity of Spanish coal chars in dry air: Effect of the addition of potassium carbonate and acetate

Abstract Several Spanish chars, ranging from lignite to anthracite, were studied in their gasification with dry air. Their behaviour was essentially related to the rank of the parent coal, and mineral matter content. Potassium was added to the demineralized char both as carbonate and acetate. Reactivity of the supported catalysts thus obtained was increased when K 2 CO 3 was the precursor salt. However, this increase was lower, and in some cases there was no increase, when potassium acetate was used. The behaviour found for the two potassium salts, was due to a greater reduction in the surface area of the char when potassium acetate was the precursor salt, which brought about a lower accessibility of the reactant gas to the active surface centres. The effect of K was inhibited in a char because of the high silica content of its ashes.

Effect of hydrogen reduction on the surface characteristics of carbon-supported iron and ruthenium catalysts

Abstract Carbons prepared by carbonization and subsequent activation of the copolymer Saran and later treated with NH 3 and HNO 3 to introduce nitrogen and oxygen surface complexes have been used as supports of Fe and Ru catalysts (5% metal loading). The effect of reduction in H 2 at 673 and 723 K on the surface properties of the catalysts has been studied by means of N 2 (77 K) and CO 2 (298 K) adsorption and mercury porosimetry. The different degrees of gasification undergone by the various types of support and the subsequent widening of microporosity are reflected in the adsorption data. An in-depth discussion of the changes in microporosity and their different effects on the S N 2 and S CO 2 values is presented, based on different adsorption mechanisms of the two adsorbates.

Adsorption of Hydrocarbons on Air-Reacted Activated Carbons. I. Adsorption Isotherms

The adsorption of several hydrocarbons (benzene, cyclohexane, n-butane, n-hexane, 2,2-dimethylbutane and isooctane) on a series of carbons resulting from the reaction of an activated carbon prepared from almond shells with air at 623 K is discussed. The results are parallel to those obtained with N2 at 77 K (González-Vilchez et al. 1979) but very different to those of CO2 at 273 and 298 K (Rodríguez-Reinoso et al. 1984). A comparison of three different ways of expressing the adsorption data is used to discuss the possible molecular sieving effect of the carbons towards the hydrocarbons.

Posterolateral Bochdalek diaphragmatic hernia in adults

Bochdalek hernias (BHs) are produced in the posterolateral area of the diaphragm. They are generally congenital, appearing in childhood, but are also detected in asymptomatic adult patients seeking medical attention for other reasons. Computed tomography (CT) or magnetic resonance imaging (MRI) is used for the correct diagnosis of the hernia type and for its localization, facilitating its management and the choice of treatment. We describe three cases of Bochdalek hernia, two on the right side and one bilateral, which was larger on the right than left side. All of these hernias contained only omental fat. In one patient, the right kidney was adjacent to the diaphragmatic defect but remained within the abdomen. The patients showed no symptoms and were not surgically treated. Examination by multislice CT with the possibility of coronal and sagittal reconstruction should be considered the standard method for diagnosing this entity. MRI in T1 is highly valuable to evaluate fat-containing chest lesions. The incidental finding of BH in asymptomatic adults is increasing, thanks to the wider application of new imaging techniques.

Hydrogenation of CO2 on Fe/carbon catalysts

The hydrogenation of CO2 on activated carbon-supported iron catalysts has been carried out at atmospheric pressure and using a H2/CO2 ratio of 4. The specific activities for this reaction are lower than those obtained for the Fischer-Tropsch synthesis using the same catalysts. CO and CH4 are the only products obtained in the hydrogenation of CO2 under the experimental conditions used. The apparent activation energies determined for the production of CO are lower than those for the production of CH4.AbstractГидрирование CO2 на железных катализаторах, нанесенных на активированный углерод, исследовано при атмосферном давлении и при соотношении H2/CO2=4. Специфическая активность для этой реакции ниже, чем в синтезе Фишера-Тропша на тех же самых катализаторах. CO и CH4 являются единственными продуктами, образующимися в гидрировании CO2 в данных экспериментальных условиях. Кажущаяся энергия активации обра-зования CO ниже, чем энергия активации образования CH4.

Porous texture characterization of coals and chars

The chemical and physical characteristics of six Spanish coals and their corresponding chars were studied. Apparent surface area, density and porosity data were determined. The apparent surface areas obtained by CO2 adsorption at 298 K and 273 K are much higher than those obtained by N2 adsorption at 77 K. This indicates that a fraction of the micropropores of the samples is not accessible to the N2 molecules. The apparent surface area and porosity of the coal samples were studied as a function of the coal rank. The changes in the porous texture of the coal samples when they are thermally converted to chars were analysed.

The n-nonane preadsorption method applied to activated carbons

The n-nonane preadsorption method has been applied to evaluate the microporosity of two series of activated carbons (prepared from olive stones and almond shells) reacted with air at 623 K to different degrees of burn-off. A detailed study of the experimental conditions needed for the successive removal of the n-nonane preadsorbed has been carried out, showing that the sample outgassed at 673 K is identical to the original. In general, the results obtained with the preadsorption of n-nonane are satisfactory only in carbons with a narrow microporosity. On the other hand, this method has been used to calculate the apparent surface area of the carbons from the n-nonane retained using an Am value of 0.844 nm2, the results being in good agreement with the N2 BET values. An analysis of the evolution with burn-off of the parameters C(BET) and D(DR) has also been carried out and their relationship calculated; both parameters describe reasonably well the evolution of the microporosity of the carbons.