Estudio de materiales de construcción neolíticos mediante diferentes técnicas instrumentales

Se han aplicado técnicas de análisis instrumental (FRX, DRX, ATR-IR, TG-ATD, SEM-EDX, MO) al estudio de fragmentos constructivos de época neolítica obtenidos de diferentes yacimientos de la Provincia de Alicante (España). La secuencia y el orden de aplicación de las técnicas se fija en función de las características y la cantidad disponible de cada muestra, estableciéndose con ello un protocolo de trabajo que se aplica siempre al resto de muestras, lo que nos permite comparar los resultados entre sí. El uso de dichas técnicas nos ha permitido la caracterización de los fragmentos constructivos, lo que nos ha llevado a conocer el grado de tecnología alcanzado por estas sociedades, sugiriéndonos que podíamos estar ante los inicios de la aplicación de la tecnología de la cal en esta zona de la Península Ibérica. En este trabajo se presenta una visión global de los resultados obtenidos hasta el momento.

Washcoated Pd/Al2O3 monoliths for the liquid phase hydrodechlorination of dioxins

The catalytic activity and durability of 2 wt.% Pd/Al2O3 in powder and washcoated on cordierite monoliths were examined for the liquid phase hydrodechlorination (LPHDC) of polychlorinated dibenzo-p-dioxins/polychlorinated dibenzofurans (PCDD/Fs), also known as dioxins. NaOH was employed as a neutralizing agent, and 2-propanol was used as a hydrogen donor and a solvent. Fresh and spent powder and monolith samples were characterized by elemental analysis, surface area, hydrogen chemisorption, scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX), and transmission electron microscopy/energy dispersive X-ray spectroscopy (TEM/EDX). Three reactor configurations were compared including the slurry and monolith batch reactors as well as the bubble loop column resulting in 100, 70, and 72% sample toxicity reduction, respectively, after 5 h of reaction. However, the slurry and monolith batch reactors lead to catalyst sample loss via a filtration process (slurry) and washcoat erosion (monolith batch), as well as rapid deactivation of the powder catalyst samples. The monolith employed in the bubble loop column remained stable and active after four reaction runs. Three preemptive regeneration methods were evaluated on spent monolith catalyst including 2-propanol washing, oxidation/reduction, and reduction. All three procedures reactivated the spent catalyst samples, but the combustion methods proved to be more efficient at eliminating the more stable poisons.

Single-walled carbon nanotube buckypapers as electrocatalyst supports for methanol oxidation

This work studies the use of various single-walled carbon nanotube (SWCNT) buckypapers as catalyst supports for methanol electro-oxidation in acid media. Buckypapers were obtained by vacuum filtration from pristine and oxidized SWCNT suspensions in different liquid media. Pt–Ru catalysts supported on the buckypapers were prepared by multiple potentiostatic pulses using a diluted solution of Pt and Ru salts (2 mM H2PtCl6 + 2 mM RuCl3) in acid media. The resulting materials were characterized via SEM, TEM, EDX and ICP-OES analysis. Well dispersed rounded nanoparticles between 2 and 15 nm were successfully electrodeposited on the SWCNT buckypapers. The ruthenium content in the bimetallic deposits was between 32 and 48 at. %, while the specific surface areas of the catalysts were in the range of 72–113 m2 g−1. It was found that the solvent used to prepare the SWCNT buckypaper films has a strong influence on the catalyst dispersion, particle size and metal loading. Cyclic voltammetry and chronoamperometry experiments point out that the most active electrodes for methanol electro-oxidation were prepared with the buckypaper supports that were obtained from SWCNT dispersions in N-methyl-pyrrolidone.

Steam reforming of ethanol over bimetallic RhPt/La2O3: Long-term stability under favorable reaction conditions

Recently, the steam reforming of biofuels has been presented as a potential hydrogen source for fuel cells. Because this scenario represents an interesting opportunity for Colombia (South America), which produces large amounts of bioethanol, the steam reforming of ethanol was studied over a bimetallic RhPt/La2O3 catalyst under bulk mass transfer conditions. The effect of temperature and the initial concentrations of ethanol and water were evaluated at space velocities above 55,000 h−1 to determine the conditions that maximize the H2/CO ratio and reduce CH4 production while maintaining 100% conversion of ethanol. These requirements were accomplished when 21 mol% H2O and 3 mol% C2H5OH (steam/ethanol molar ratio = 7) were reacted at 600 °C. The catalyst stability was assessed under these reaction conditions during 120 h on stream, obtaining ethanol conversions above 99% during the entire test. The effect of both H2 and air flows as catalyst regeneration treatments were evaluated after 44 and 67 h on stream, respectively. The results showed that H2 treatment accelerated catalyst deactivation, and air regeneration increased both the catalyst stability and the H2 selectivity while decreasing CH4 generation. Fresh and spent catalyst samples were characterized by TEM/EDX, XPS, TPR, and TGA. Although the Rh and Pt in the fresh catalyst were completely reduced, the spent samples showed a partial oxidation of Rh and small amounts of carbonaceous residue. A possible Rh–Pt–Rh2O3 structure was proposed as the active site on the catalyst, which was regenerated by air treatment.

Cabezo Pardo. Análisis instrumental de materiales de construcción de barro del yacimiento argárico

Partiendo del análisis instrumental de cuatro pequeños fragmentos constructivos se intenta, en lo posible, contestar a una serie de cuestiones básicas señaladas por algunos autores (De Chazelles y Poupet, 1989: 10-11; Sánchez García, 1995: 350; 1997: 142) para poder comprender el nivel técnico de una época o cultura y la evolución de sus técnicas constructivas, en este caso aplicadas a la fase argárica del yacimiento del Cabezo Pardo.

Pt- and Ru-Doped SnO2–Sb Anodes with High Stability in Alkaline Medium

Different Pt- and Ru-doped Ti/SnO2–Sb electrodes were synthesized by thermal decomposition. The effect of the gradual substitution of Sb by Ru in the nominal composition on the physicochemical and electrochemical properties were evaluated. The electrochemical stability of the electrodes was estimated from accelerated tests at 0.5 A cm–2 in 1 M NaOH. Both as-synthesized and deactivated electrodes were thoroughly characterized by scanning electron microscopy (SEM), energy-dispersive X-ray microanalysis (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction analysis (XRD). The incorporation of a small amount (about 3 at. %) of both Pt and Ru into the SnO2–Sb electrodes produced a 400-times increase in their service life in alkaline medium, with no remarkable change in the electrocatalysis of the oxygen evolution reaction (OER). It is concluded that the deactivation of the electrodes is promoted by alkaline dissolution of metal species and coating detachment at high potentials. The introduction of Pt has a coating compacting effect, and Ru(IV), at low amounts until 9.75 at. %, replaces the Sn(IV) cations in the rutile-like SnO2 structure to form a solid solution that strongly increases the stability of the electrodes. The observed Ru segregation and decreased stability for larger Ru contents (x > 9.75 at. %), together with the selective dissolution of Ru after deactivation, suggest that the formation of a homogeneous (RuδSn1−δ)O2 single-phase is crucial for the stabilization of these electrodes.

Galanet (Elche): análisis químico instrumental de los materiales de construcción

En el caso del yacimiento de Galanet sólo se han documentado 15 fragmentos de este tipo. Con estos condicionantes y a partir del análisis instrumental de tres de estos fragmentos intentaremos, dentro de los posible, responder a una serie de cuestiones que algunos autores (De Chazelles, Poupet, 1989, 10-11; Sánchez García, 1995, 350, Sánchez García, 1997, 142) han señalado como básicas para poder comprender el nivel técnico de una época o cultura y la evolución de sus técnicas constructivas, en este caso aplicadas al yacimiento de Galanet: -Determinar la procedencia del material utilizado. -Saber si la elección del material utilizado se debe a imperativos geológicos o prima en ella una decisión antrópica. -Si el material se ha usado en bruto o ha sufrido algún tratamiento previo. -Si la mayoría de las estructuras analizadas presentan una misma composición o por el contrario se utilizan diferentes composiciones en función del tipo de estructura. -Si la técnica utilizada es propia de una cronología, etapa cultural o área geográfica determinada con lo que se constituiría en un indicador cultural o por el contrario es inespecífica. -Si las soluciones técnicas empleadas son fruto del desarrollo interno de las fuerzas productivas o se deben a influencias foráneas. Es evidente que parte de estas cuestiones no se podrán contestar dado que solo contamos con unos pequeños fragmentos de material constructivo de apenas unos pocos centímetros y, sobre todo, que desconocemos cualquier detalle sobre el área de habitación del poblado de Galanet. Pero, al menos, intentaremos contribuir a conocerlo mejor.

Gold Nanoparticles Supported on Polyacrylamide Containing a Phosphorus Ligand as an Efficient Heterogeneous Catalyst for Three-Component Synthesis of Propargylamines in Water

Gold nanoparticles supported on a polyacrylamide containing a phosphinite ligand have been synthesized and characterized using different techniques such as TEM, SEM, EDX, XPS, and solid UV analyses. The new material was successfully applied as a heterogeneous catalyst for the three-component A3 coupling of amines, aldehydes, and alkynes to give propargylamines. Reactions are performed in neat water at 80 °C with only 0.05 mol% catalyst loading. The heterogeneous catalyst is recyclable during seven consecutive runs with small decrease in activity.