Francesc Medina

Different morphologies of silver nanoparticles as catalysts for the selective oxidation of styrene in the gas phase

Silver nanoparticles of different morphologies were prepared using the polyol process and then dispersed on alpha-alumina. Catalysts were tested for the selective oxidation of styrene in the gas phase. Activity and selectivity were strongly dependent on the morphology of the silver nanoparticles.

Nanoplatelet-based reconstructed hydrotalcites: towards more efficient solid base catalysts in aldol condensations

Rehydration of Mg-Al hydrotalcite in the liquid phase using ultrasounds or a high stirring speed leads to nanoplatelets with surface areas of 400 m(2) g(-1), displaying catalytic activities in aldol condensations up to 8 times higher than the best catalytic system reported in the literature.

Cobalt hydrotalcite for the steam reforming of ethanol with scarce carbon production

Co/Mg/Al hydrotalcite-type catalysts have been loaded onto ceramic honeycombs and tested in the ethanol steam reforming (ESR) reaction for producing hydrogen under practical conditions. In contrast with previously reported cobalt-based systems, the formation of carbon was scarce. This has been ascribed to the unique formation of traces of metallic cobalt particles under reaction conditions, as inferred from HRTEM, magnetic measurements, and in situ X-ray photoelectron spectroscopy (XPS) experiments. The best catalytic performance has been exhibited by the catalyst derived from the hydrotalcite with a Co:Mg:Al molar ratio of 1:2:1, where CoAl spinel and CoO strongly interacting with MgO phases have been identified.

Boosted CO2 reaction with methanol to yield dimethyl carbonate over Mg–Al hydrotalcite-silica lyogels

Nonimmobilized and immobilized Mg-Al hydrotalcite-like materials on silica lyogels were prepared and activated by calcination to be tested as catalysts in the direct carboxylation reaction of methanol. The HTs supported on silica lyogels showed an important improvement and high stability in the direct synthesis reaction of DMC from CO2 and MeOH.

Biohydrogen production by dark fermentation of glycerol using Enterobacter and Citrobacter Sp

Glycerol is an attractive substrate for biohydrogen production because, in theory, it can produce 3 mol of hydrogen per mol of glycerol. Moreover, glycerol is produced in substantial amounts as a byproduct of producing biodiesel, the demand for which has increased in recent years. Therefore, hydrogen production from glycerol was studied by dark fermentation using three strains of bacteria: namely, Enterobacter spH1, Enterobacter spH2, and Citrobacter freundii H3 and a mixture thereof (1:1:1). It was found that, when an initial concentration of 20 g/L of glycerol was used, all three strains and their mixture produced substantial amounts of hydrogen ranging from 2400 to 3500 mL/L, being highest for C. freundii H3 (3547 mL/L) and Enterobacter spH1 (3506 mL/L). The main nongaseous fermentation products were ethanol and acetate, albeit in different ratios. For Enterobacter spH1, Enterobacter spH2, C. freundii H3, and the mixture (1:1:1), the ethanol yields (in mol EtOH/mol glycerol consumed) were 0.96, 0.67, 0.31, and 0.66, respectively. Compared to the individual strains, the mixture (1:1:1) did not show a significantly higher hydrogen level, indicating that there was no synergistic effect. Enterobacter spH1 was selected for further investigation because of its higher yield of hydrogen and ethanol.

Simultaneous in situ generation of hydrogen peroxide and Fenton reaction over Pd–Fe catalysts

High mineralization degree of organic compounds can be achieved by a novel environmentally-friendly full heterogeneous Pd-Fe catalytic system, which involves in situ generation of hydrogen peroxide from formic acid and oxygen, and oxidation of organic compounds by Fenton process in a one-pot reaction.

Hydrogen substitutes for the in situ generation of H2O2: An application in the Fenton reaction

This study investigates the ability of formic acid, hydrazine and hydroxylamine to act as H(2) substitutes in conducting phenol degradation by Fenton reaction using in situ generated hydrogen peroxide. The processes were performed with semi-heterogeneous (Pd/Al(2)O(3)+soluble Fe(2+)) and fully heterogeneous (FePd/Al(2)O(3)) catalytic systems under ambient conditions. In contrast to bulk H(2)O(2) production conditions, hydrazine is able to produce H(2)O(2)in situ followed by phenol degradation using Pd/Al(2)O(3)+Fe(2+) at pH 3 without the need for halide ions. However, a degree of mineralization exceeding 37% could not be achieved. The significant production of in situ H(2)O(2) at the inherent acidic pH of hydroxylammonium sulfate in the presence of Pd/Al(2)O(3)+Fe(2+) was also found to differ from the bulk production of H(2)O(2), in which no H(2)O(2) was detected. A remarkable degree of mineralization (ca. 65%) as well as fast phenol degradation during the reaction started at pH 7 over FePd/Al(2)O(3) may be an advantage of using hydroxylamine. On the other hand, using formic acid, H(2)O(2) was produced at a moderate rate, thereby achieving higher efficiency in the mineralization of phenol. Most importantly, the catalysts were more stable in the presence of formic acid than hydrazine or hydroxylamine.

Characterization and catalytic properties of several LaNi and SrNi solids

Abstract The structural characterization using BET, XRD, TPR, XPS, SEM and TPD, and the catalytic behaviors of several La Ni and Sr Ni samples compared with those previously reported on K Ni and undoped nickel catalysts have been studied for the hydrogenation reaction of adiponitrile. BET and XRD show the increase of area and the sintering inhibition of the nickel particles due to the presence of both lanthanum and strontium, respectively. XPS shows a high lanthanum migration from the bulk to the surface of the nickel catalysts with respect to Sr Ni and K Ni samples and also a decrease of the reduction degree of the samples with the increase of lanthanum or strontium content. The latter effect has also been observed by TPR, XRD and BET and is in agreement with those potassium-doped nickel catalysts. According to TPD results lanthanum and strontium do not significantly modify, either the metal-hydrogen, metal-amine and metal-adiponitrile interactions or its blocking capability upon any particular active nickel site, when both are compared with the undoped nickel. These behaviors agree with the catalytic results as lanthanum/nickel and strontium/nickel catalysts show higher conversions and lower selectivities to primary amines than those obtained from the previously reported potassium doped nickel catalysts

Size and aspect ratio control of Pd2Sn nanorods and their water denitration properties

Monodisperse Pd2Sn nanorods with tuned size and aspect ratio were prepared by co-reduction of metal salts in the presence of trioctylphosphine, amine, and chloride ions. Asymmetric Pd2Sn nanostructures were achieved by the selective desorption of a surfactant mediated by chlorine ions. A preliminary evaluation of the geometry influence on catalytic properties evidenced Pd2Sn nanorods to have improved catalytic performance. In view of these results, Pd2Sn nanorods were also evaluated for water denitration.

Uranium removal from a contaminated effluent using a combined microbial and nanoparticle system.

Reduction of soluble uranium(VI) to insoluble uranium(IV) for remediating a uranium-contaminated effluent (EF-03) was examined using a biotic and abiotic integrated system. Shewanella putrefaciens was first used and reduced U(VI) in a synthetic medium but not in the EF-03 effluent sample. Subsequently the growth of autochthonous microorganisms was stimulated with lactate. When lactate was supported on active carbon 77% U(VI) was removed in 4 days. Separately, iron nanoparticles that were 50 nm in diameter reduced U(VI) by 60% in 4 hours. The efficiency of uranium(VI) removal was improved to 96% in 30 min by using a system consisting of lactate and iron nanoparticles immobilized on active carbon. Lactate also stimulated the growth of potential uranium-reducing microorganisms in the EF-03 sample. This system can be efficiently used for the bioremediation of uranium-contaminated effluents.