This work reports the study of the catalytic oxidation of toluene (1400 ppm) on Pd and Pt catalysts supported over alumina promoted with 1 and 10 wt% Ce. Catalysts were characterized by: physical adsorption N2 (BET), XRD, UV-VIS, FTIR of adsorbed pyridine, FTIR od the CO adsorption, XPS and TPO. The results showed a decrease in the number of acid sites with the loading of Ce in the catalyst. It was observed higher dispersion on Pd than on Pt catalysts. For Pt catalysts only Pt0 species was detected while in palladium catalysts Pd0 and Pd2+ species were observed. For both series of catalysts total combustion was reached on the catalysts containing 1% of Ce, Pt/ACe1, and Pd/ACe1 catalysts, at 300ºC. For Pd catalysts the maximum in activity depended on the redox optimal ratio (Ce3+/ Ce4+, Pd0/ Pd2+) ant the activation time for the calalyst was important. The catalytic combustion of toluene on Pt was favored on reduced surface through a process of demethylation. The depot of carbon on catalyst decreased with Ce contents due to redox properties of the cerium oxide.

El presente trabajo reporta el estudio de la oxidación catalítica de tolueno (1400 ppm) en catalizadores de Pd y Pt soportados en alúmina promovida con 1 y 10% en peso de Ce. Los catalizadores se caracterizaron por: adsorción física de N2 (BET), XRD, FTIR de piridina adsorbida, FTIR de la adsorción de CO, XPS y TPO. Los resultados mostraron disminución en el número de sitios ácidos con el contenido de cerio en el catalizador. Se observó una mayor dispersión en los catalizadores de Pd que en los de Pt. En los catalizadores de Pt sólo se detectaron especies de Pt0 mientras que en Pd se detectaron especies de Pd0 y Pd2+. En ambas series de catalizadores la combustión total se alcanzó a contenidos de 1% peso en Ce, catalizadores Pd/ACe1 y Pt/ACe1, a 300ºC. En el caso del Pd la combustión de tolueno dependen de las propiedades redox óptimas (Ce3+/ Ce4+, Pd0/ Pd2+) por lo que resulta importante el tiempo de activación del catalizador. La combustión catalítica de tolueno en Pt se vio favorecida en una superficie reductora por un proceso de demetilación. El depósito de carbono en el catalizador disminuyó con el contenido de cerio en el catalizador debido a las propiedades redox del óxido de cerio.

TiO2 supported Ag nanoparticles with metal loading ranging from 2.0 to 12.0 wt.% have been prepared by reduction of a silver precursor with formic acid under mild conditions. XPS showed that silver remains in a reduced state and TEM has demonstrated that the procedure was effective to produce silver nanoparticles. Only small changes in the metal particle size from 2.0-3.4 nm occurs when the Ag content increases from 2.0 to 12.0 wt.%. O2 TPD has revealed the presence of different types of adsorbed oxygen species being the one assigned to the active specie called Ob which one displayed the highest proportion in the catalysts with higher metal loading. Catalytic activity in the conversion of methanol to formaldehyde showed that those samples with metal loading higher than 7.0 wt% displays higher yields compared to the unsupported silver catalyst.

The Fischer Tropsch reaction, using a simulated gas mixture similar to that obtained from biomass transformation (biosyngas), was studied over Fe/SiO2catalysts. The reaction was carried out in a stainless steel fixed bed reactor at 300 °C and 1 MPa. Excess solvent impregnation was used to prepare the catalysts. Nitrogen adsorption at -196 °C, thermal programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) were used as characterization methods. The highest CO conversion was obtained for the catalyst with Fe-loading of 15wt% whereas it decreased at higher Fe loadings. The decrease ofthe activity is explained in terms ofthe drop ofthe active sites due to the formation of large Femetallic aggregates. The Fe/SiO2 catalysts presented a wide distribution of liquid hydrocarbons (C6 to C 18) and high methane formation. The liquid product distribution was related to the average size of iron particles. The increase of iron particle size favours the formation of hydrocarbons centred in C 11-14 chain length.

The photocatalytic degradation of trichloroethylene over Ag nanoparticles supported on TiO2 was studied. The photocatalysts were obtained by impregnation of Ag colloids on TiO2. They were characterized by XPS, TEM and UV-vis. Ag° nanoparticles were obtained with diameters between 2.0-3.2 nm. The photocatalysts were found to display band gap energies similar to those of pure TiO2, although the presence of Ag nanoparticles results in the formation of a plasmon resonance band in the visible range. The photocatalytic activity of the Ag/TiO2 samples to remove trichlorethylene (TCE) in gas phase was tested. With visible light, up to 60% of conversion was obtained.

The citronellal hydrogenation was studied on Ir/Nb(2)0(5)-Si0(2) catalysts. Aseries of catalysts was synthesized with different niobia contents (Ir/Nl 1.10%; Ir/N2 2.54%; Ir/N3 3.25%; Ir/N4 5.30%wt%) using the wet impregnation method. These catalysts were reduced in hydrogen atmosphere at low or high temperatures. 473K (LTR) or 773K respectively. Their structural and surface properties were investigated by XRD, TEM, XPS, DTP, FTIR, H2 chemisorption at 298 K and surface specific area by using the BET method. The X ray diffraction studies revealed only the peaks due to niobia, mainly in those with higher niobia loading. No diffraction lines due to Ir were observed due to its lower content and/or to its high dispersion. The catalytic tests in the hydrogenation of citronellal were carried out in a batch reactor operated at 6.2 bar of H2 and 343 K. All catalysts showed higher selectivity to isopulegol and to their products due to the cyclization of the citronellal molecule.

The solvent effect in the citral hydrogenation over iridium catalysts has been studied. The catalysts used in this research were, the monometallic Ir/ TiO2 reduced at low or high temperature (LT y HT) and the bimetallic Ir-Fe/TiO2 (LT y HT) catalysts. As solvent n-heptane, an equimolar mixture n-heptane-1-propanol and 1-propanol were used. The reactions were carried out at a hydrogen pressure of 8.27 bar and at 363 K. In the LT catalyst, the catalytic activity increases upon the addition of Fe3+. This positive effect was obtained keeping constant the selectivity to the unsaturated alcohol, being 100% selective to the products obtained by hydrogenation of the C=O bond. In the HT catalysts, both the addition of Fe and the presence of TiOx moieties generated by the strong metal support interaction (SMSI) effect, lead to an increase of surface acidity. In LT and HT catalysts, an increase in the polarity of the solvent increases the catalytic activity, however the reaction pathway is modified by the presence of acid sites which in polar solvents allow the formation of acetals, mainly in the HT catalysts

The enantioselective hydrogenation of 1-phenyl-1,2-propanedione at 298 K and 40 bar over modified supported iridium catalysts has been studied. Cinchonidine has been used as chiral inducer. The catalysts were obtained by impregnation of Ir(acac)3 on three different supports: SiO2, TiO2 and MoO3, followed by calcination in air and reduction under hydrogen at 773 K. All the solids were characterized by nitrogen adsorption-desorption isotherms at 77 K, H2 chemisorption, XRD, TEM, TPR and XPS. It was found that Ir/SiO2 and Ir/TiO2 catalysts reduced at high temperatures, 773 K, possess similar metal particle size, close to 2.0 nm, eventhough the H/Ir ratio obtained from H2 chemisorption showed larger differences, with the H/Ir ratio being lower for titania- and molybdenum-supported iridium catalysts. In these samples, migration of the partially reduced supports, TiOx and MoOx moieties, on the metal crystals induce the creation of Irdelta+ species. TPR and XPS results confirmed that the metal component was not completely reduced. The activity was influenced by the nature of the support, being more active those in the SMSI state such as Ir/TiO2 and Ir/MoO3 being more active. This has been attributed to the presence of electron deficient metal species, Irdelta+, which are responsible for the polarization of the carbonyl bond of the substrates, thus favoring the activity and enantioselectivity of the reaction. The effect of different solvents on the activity and the enantioselectivity of the reaction was also studied. The highest enantiomeric excess (ee) of (R)-1-phenyl-1-hydroxy-2-propanone (20%) was obtained with the Ir/TiO2 catalyst using acetic acid as solvent

Titania-supported iron (1wt%) catalysts were prepared by the sol-gel method using different gelation pH (3 and 9), metal precursors (FeCl2 and FeCl3) and calcination temperatures (873 and 1073K). Characterization data of calcined catalysts revealed that in all samples the dominant iron species is Fe3+ and the crystalline phase of the TiO2 substrate depends on the gelation pH and the metal precursor used. It was found that in the Fe/TiO2 ex-FeCl3 samples an important part of the iron ions became inserted in titania lattice, which makes the anatase phase stable even at high calcination temperatures. The solids were tested in the combustion of methane under stoichiometric conditions at atmospheric pressure. It was observed that the Fe/TiO2 ex-FeCl2 sample displays the highest activity. This behaviour is explained on the basis of the highest fraction of iron oxide deposited on the external surface of the catalyst particles

Se prepararon catalizadores de hierro soportados sobre titania utilizando el método sol-gel y contenido de metal de 1% en peso. Se utilizaron diferentes pH de gelación (3 y 9), precursores metálicos (FeCl2 y FeCl3) y temperaturas de calcinación (873 y 1073K). Los resultados de caracterización indican que en todos los casos el hierro está presente fundamentalmente como Fe3+ y la fase cristalina de titanio presente depende del pH de gelación y de la naturaleza del precursor utilizado. Se encontró que cuando se usa FeCl3 como precursor de hierro, hay una mayor inserción de iones hierro en la red de la titania que estabiliza a la fase anatasa aún a altas temperaturas de calcinación. Se midió la actividad catalítica de los sólidos preparados en la reacción de combustión de metano en relaciones estequiométricas metano/oxígeno y a presión atmosférica. Los catalizadores preparados a partir de FeCl2 mostraron la mayor actividad. Este comportamiento se explica considerando que en estos catalizadores la mayor parte del hierro se encuentra en la superficie externa del sólido presentando sólo una pequeña fracción de iones hierro insertos en la red de titanio.

Catalytic combustion of toluene on silica supported Pd, Pd-Cu and Cu catalysts has been investigated. The solids were prepared by the impregnation method and they were characterized by evaluation of surface area, metal dispersion and surface composition. The reaction was studied under stoichiometric conditions in the presence and absence of thiophene as poison. It was found that the presence of copper reduces the activity due to a copper-palladium interaction, which modifies the nature of the active site. The monometallic Pd and the bimetallic Pd-Cu catalysts showed high resistance to the sulfur poisoning

Se estudió la combustión catalítica de tolueno sobre catalizadores de Pd, Pd-Cu y Cu soportados sobre sílice preparados por el método de impregnación. Los sólidos se caracterizaron por medidas de superficie específica, dispersión metálica y composición superficial. La actividad catalítica de ellos se midió en la reacción de combustión de tolueno realizada en condiciones estequiométricas de oxígeno en ausencia y presencia de un veneno azufrado, como tiofeno. Se encontró que la presencia de cobre disminuye la actividad del paladio debido a una modificación electrónica paladio-cobre, que modifica la naturaleza del sitio activo. El catalizador monometálico de Pd y los bimetálicos Pd-Cu muestran una alta resistencia al envenenamiento por el compuesto azufrado.

The vapor-phase hydrogenation of crotonaldehyde on Rh supported catalysts has been studied. The effect of some variables of preparation in catalysts prepared by the sol-gel and impregnation methods on the surface and catalytic properties were analyzed. It was found, that the porosity of the support has a small effect on the selectivity to the unsaturated alcohol and the presence of partially reducible supports such as ZrO2 and TiO2, may increase the selectivity to crotyl alcohol via an enhancement of the polarization of the C=O bond as a result of surface decoration of the metal component. The presence of chlorine ions in the metal-support interfacial region, also allows, in a certain extension, a polarization of the carbonyl bond

Se estudió la hidrogenación en fase vapor de crotonaldehído sobre catalizadores de Rh soportados. Se analizó la influencia de diferentes variables de preparación de catalizadores obtenidos por el método sol-gel y por impregnación. Se encontró que la porosidad del soporte tiene sólo un pequeño efecto sobre la selectividad hacia el alcohol insaturado y que la presencia de soportes parcialmente reducibles como ZrO2 y TiO2 pueden incrementar la selectividad hacia el alcohol crotílico a través de un aumento de la polarización del enlace C=O como consecuencia de una decoración superficial del componente metálico. Adicionalmente, la presencia de iones cloruro en la interfase metal-soporte, también contribuyen en alguna medida a la polarización del enlace carbonílico

Cu-ZnO-Al2O3 catalysts for the low-temperature water-gas shift reaction were prepared using methods of direct and reverse coprecipitation. The catalysts obtained were characterized by DRX, TPR, XPS, N2O chemisorption, Hg-Porosimetry and BET surface area. It was observed that the precipitation sequence of the precursors led to significant differences in values of copper dispersion and consequently in the activity of the catalyst for the water-gas shift reaction.