In this work, a series of Pt-CuO(x)/C materials with different metal oxide contents were evaluated as electrocatalysts for the glycerol oxidation reaction (GOR) in an alkaline medium. CuO nanoparticles of ca. 6 nm were prepared by a precipitation/calcination route and incorporated into the carbon support with a weight percentage from 0 to 30. Platinum nanoparticles of ca. 3 nm were deposited over the different hybrid CuO(x)/C materials via the ethylene glycol reduction under pulsed microwave heating conditions. The electrochemical experiments showed that the onset potential for the GOR on the bimetallic Pt-CuO(x)/C electrodes is shifted negatively by ca. 160 mV, and the charge transfer resistance is significantly reduced compared to Pt/C, indicating that CuO facilitates both the electron charge transfer kinetics and the oxidation of the adsorbed intermediates. The most active electrode material, Pt-CuO(30)/C (30 wt % CuO on carbon), developed 3.5 times higher activity than Pt/C. This bimetallic electrode retained more than 90% of its initial activity after an accelerated cycling test.

The phase relationship, defect formation, and incorporation of Ni in Ce0.9Zr0.1O2 have been investigated in samples of nominal composition (Ce0.9Zr0.1)(1-x)NixO2-delta with x=0.03, 0.05 and 0.1, synthesized by a cation complexation route and heat treated at 600, 800 and 1000 degrees C. Several structural (XRD, XAS, HRTEM) and spectroscopic (XPS, Raman) techniques have been used. Our data show the lattice parameters determined from XRD do not significantly vary with the Ni content or annealing temperature. The increasing defect concentration with increasing Ni content revealed by Raman spectra was associated to the formation of oxygen vacancies in the bulk due to coexistence of NiO and Ce0.9Zr0.1O2. On the other hand, no variation in the oxygen vacancies concentration was detected at the surface with increasing the Ni content by XPS data. In those samples with the lowest Ni concentrations (3 and 5 %) and heat treated at 600 degrees C, the analysis of the EXAFS zone of the K-edge of Ni indicates that local order around Ni cations is not long-range, suggesting the presence of a noncrystalline phase. When the Ni content is higher (10 %) and/or the temperature of the thermal treatment is increased, the crystallization of NiO is clearly detected by XRD, EXAFS and HRTEM.

The influence of manganese modification on the spectroscopic features of manganese-doped CeO2 systems synthesized by the microwave-assisted hydrothermal route and their correlation with the presence of O defective structures were verified, focusing on their interaction with poisonous atmospheres. Raman and electron paramagnetic resonance studies confirmed the presence of defective clusters formed by dipoles and/or quadrupoles. The number of paramagnetic species was found to be inversely proportional to the doping concentration, resulting in an increase in the Mn2+ signal, likely due to the reduction of Mn3+ species after the interaction with CO. X-ray photoelectron spectroscopy data showed the pure system with 33% of its cerium species in the Ce3+ configuration, with an abrupt decrease to 19%, after the first modification with Mn, suggesting that 14% of the Ce3+ species are donating one electron to the Mn2+ ions, thus becoming nonparamagnetic Ce4+ species. On the contrary, 58% of the manganese species remain in the Mn2+ configuration with five unpaired electrons, corroborating the paramagnetic feature of the samples seen in the electron paramagnetic resonance study.

Herein, Pt and Pt0.85Cu0.15 nanoparticles were deposited over hybrid CuO/C supports (1.5, 3 and 5 wt.% on carbon) by a pulsed microwave-assisted reduction method and the as-prepared materials were evaluated as electrocatalysts toward the electrooxidation of glycerol in alkaline medium. The structural and morphological analysis showed that the platinum particles decrease from 4.2 nm to around 3.0 nm in size when the CuO crystallites are present on the surface of the carbonaceous material. The electrochemical experiments indicated that the nanoparticles deposited over the hybrid support present significantly improved electrocatalytic prop-erties compared to Pt/C. Among them, Pt0.85Cu0.15 CuO(3)/C catalyst exhibited the best performance for the GOR, delivering a mass activity of around 270 mA mg(Pt)(-1) at a fixed potential of 0.7 V, which is 5.4 times higher than that of Pt/C (similar to 50 mA mg(Pt)(-1)). The results showed that the addition of very small amounts of copper oxide on the surface of the carbonaceous support and the addition of a small amount of Cu to Pt boost the activity of the active sites via the bifunctional mechanism, geometric strain and ligand effects.

The effect of sodium hydroxide (NaOH) on the size of palladium (Pd) nanoparticles obtained by the simple polyol route was studied. Nanoparticles were synthesized at room temperature using palladium(II) chloride (PdCl2) and NaOH dissolved in ethylene glycol (EG) as reduction reaction promoters. No protective agents or stabilizers were used. We monitored the reaction kinetics and the growth of the nanoparticles by UV-vis spectroscopy and their crystallinity by powder X-ray diffraction (XRD) as a function of NaOH concentration. Crystallite size was evaluated from the diffraction pattern. We found that nanoparticle growth is strongly influenced by the NaOH: Pd molar ratio. Crystallite sizes from 2 to 24 nm were obtained for molar ratios ranging from 1 to 33. At lower concentrations of NaOH, the nucleation and growth process of the nanoparticles were found to be controlled by the reduction of the Pd ion precursors.At higher concentrations, the intermediate reduction of Pd-Cl-OH species determines the nanoparticle growth rate resulting in the formation of the smallest final-size nanoparticles.

This work investigates the electrooxidation of glycerol in an alkaline environment at non-doped and P-doped Pt-alpha Ni(OH)(2) nanoparticles supported on oxidized Vulcan XC-72R carbon. Pt-alpha Ni(OH), and PtP-alpha Ni(OH)(2) particles with sizes in the range of 3-5 nm were obtained via a one-step chemical reduction approach. The physicochemical characteristics of the as-prepared catalysts were studied by inductively coupled plasmaoptical emission spectrometry (ICP-OES), energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and x-ray diffraction (XRD) techniques. It was determined that the incorporation of phosphorus lead to the formation of amorphous PtP-alpha Ni(OH)(2) deposits. TEM analysis showed that the incorporation of phosphorus into the bimetallic Pt-alpha Ni(OH)(2 )catalyst origins a remarkable reduction in the average size of the nanoparticles with a narrow size distribution. A substantial improvement in the electrocatalytic properties of the Pt-alpha Ni(OH)(2) system toward the oxidation of glycerol was observed through P doping. The P-doped electro-catalysts developed a mass current density of 60.3 mA mg(pt)(-)(1) at 765 mV vs. RHE, which is about 5 and 45 times higher than those of commercial PtRu/C (12.3 mA mg(pt)(-1)) and as-synthesized Pt-alpha Ni(OH)(2)/C (1.5 mA mg(pt)(-1)), respectively. The temperature-dependent experiments displayed that the apparent activation energy for the reaction is halved upon the addition of phosphorus.

In this work, the influence of Cu-doping on the ability of NiO co-catalyst to enhance the electrocatalytic properties of carbon-supported Pt nanoparticles toward ethanol and glycerol oxidation was investigated. The Cu-doped NiO particles were synthesized by a precipitation method, while the noble metal nano-particles were deposited over the hybrid Cu-doped NiO/C supports via a pulsed microwave-assisted polyol method using ethylene glycol as reductant. Pt-NiO and Pt-NiOCuO(x:y)/C catalysts with Ni:Cu atomic ratios of 9:1 (Pt-NiOCuO(9:1)/C), 7:3 (Pt-NiOCuO(7:3)/C) and 5:5 (Pt-NiOCuO(5:5)/C) were obtained. The physicochemical analysis showed that the as-prepared catalysts are composed of nanoparticles of about 3 nm. The potentiostatic experiments exhibited that the Pt-NiOCuO( 7:3)/C catalyst is the most active catalyst for ethanol oxidation, while the Pt-NiOCuO(5:5)/C catalyst exhibited the best performance for glycerol oxidation. These catalysts developed mass current densities of almost 12 and 5 times higher than those of bare Pt/C for ethanol and glycerol oxidation reactions, respectively. Moreover, an accelerated multicycling stability test displayed that the as-prepared catalysts retain almost 98% of their initial mass current density. (c) 2022 Published by Elsevier B.V.

In the synthesis of metallic nanoparticles in microemulsions, we hypothesized that the particle size is controlled by the reaction rate and not by the microemulsion size. Thus, the changes observed in the particle sizes as reaction conditions, such as concentrations, temperatures, the type of surfactant used, etc., are varied which should not be correlated directly to the modification of these conditions but indirectly to the changes they produce in the reaction rates. In this work, the microemulsions were formulated with benzene and water as continuous and dispersed phases, respectively, using n-dodecyltrimethylammonium bromide (DTAB) and n-octanol as the surfactant and cosurfactant. Using time-resolved UV-vis spectroscopy, we measured the reaction rates in the production of palladium (Pd) nanoparticles inside the microemulsions at different reactant concentrations and temperatures, keeping all the other parameters constant. The measured reaction rates were then correlated with the particle sizes measured by transmission electron microscopy (TEM). We found that the nanoparticle size increases linearly as the reaction rate increases, independently of the actual reactant concentration or temperature. We proposed a simple model for the observed kinetics where the reaction rate is controlled mainly by the diffusion of the reducing agent. With this model, we predicted that the particle size should depend indirectly, via the reaction kinetics, on the micelle radius, the water volume and the total microemulsion volume. Some of these predictions were indeed observed and reported in the literature.

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Four carbon supported trimetallic PtNiCu nanostructured catalysts have been successfully synthesized by a two-step chemical/electrochemical reduction route. Nanoparticles with average sizes in the range of 2.2-3.5 nm with mixed alloy, pseudo core-shell and core-shell patterns were obtained. All as-prepared electrocatalysts exhibited high electroactive surface areas, ranging from 93 to 117 m(2) g(-1). The electrocatalytic activity of the trimetallic materials towards the ethanol oxidation reaction (EOR) was studied by cyclic voltammetry and chronoamperometry at temperatures between 20 and 60 degrees C. Among the studied catalysts, the alloy nanomaterial with a Pt:Cu:Ni surface atomic ratio of 36.8:57.0:6.2 and the pseudo core-shell material with a Pt:Cu:Ni surface atomic ratio of 18.0:43.6:38.4 exhibited the best performance for the EOR. These nanostructured catalysts presented lower onset potentials, four times higher mass activities, and 8-10 times higher specific activities than a commercial PtRu/C catalyst. The kinetic parameters (i.e., Tafel slope and apparent activation energy) indicated that the electro-oxidation of ethanol on the as-prepared catalysts was faster than on PtRu/C. (C) 2019 Elsevier Ltd. All rights reserved.

RESUMEN El efecto electrocatalítico de nanopartículas bimetálicas de Cd y Ag soportadas sobre sustratos de grafito pirolítico altamente orientado (HOPG) y carbón vítreo (CV), fue evaluado para la reacción de reducción de iones nitrato y/o nitrito. Para ello, se obtuvieron inicialmente, los depósitos metálicos y bimetálicos sobre los sustratos carbonosos (SC) empleando la técnica electroquímica de simple pulso potenciostático. En el caso del par bimetálico, la cantidad de Cd fue depositada selectivamente sobre las nanopartículas de Ag previamente soportadas sobre HOPG o CV, debido a la fuerte interacción entre ambos metales, empleando diferentes tiempos de polarización. Los estudios potenciodinámicos del sistema Cd-Ag/SC, indicaron que, a tiempos de polarización relativamente grandes, es factible que los átomos de Ag y Cd formen una aleación superficial, debido a un proceso de interdifusión entre ellos, pudiendo afectar su actividad catalítica. Las partículas generadas sobre HOPG, fueron caracterizadas por AFM ex-situ y XPS, corroborando este último análisis la formación de una aleación Cd-Ag. Posteriormente, los electrodos modificados con nanopartículas metálicas y bimetálicas, y también los sustratos libres de depósitos, fueron analizados mediante voltamperometría cíclica en una solución conteniendo iones nitrato. Se detectó que los procesos de reducción de iones nitrato y/o nitrito comienzan a valores de potenciales más positivos para el caso de los depósitos bimetálicos, correspondiendo a un efecto catalítico más pronunciado debido a la presencia de Cd y Ag, los cuales pueden encontrar-se aleados en la superficie, produciendo un efecto sinérgico hacia la reducción de los aniones. Incluso, se verificó un cambio en el comportamiento catalítico para mayores tiempos de polarización empleados en la deposición del Cd sobre las nanopartículas de Ag soportadas, que puede estar relacionado con la formación de dicha fase aleada. Los productos de reacción fueron analizados por colorimetría y cromatografía de intercambio iónico determinándose cantidades de nitrato, nitrito y amonio en solución.

The electrocatalytic effect of Cd-Ag bimetallic nanoparticles supported on highly oriented pyrolytic graphite (HOPG) and vitreous carbon (VC) substrates was evaluated for the nitrate and/or nitrite ions reduction reaction. For this, in a first stage, the metallic and bimetallic deposits were obtained on the carbonaceous substrates (CS) using the electrochemical technique of the single potentiostatic pulse. In the case of the bimetallic pair, the amount of Cd was selectively deposited on the Ag nanoparticles previously supported on HOPG or CV, due to the strong interaction between the two metals, using different polarization times. Potentiodynamic studies of the system Cd-Ag/(CS) indicated that, for relatively large polarization times, it is feasible the formation of a surface alloy between Ag and Cd atoms, due to an interdiffusion process between them, which may affect its catalytic activity. The generated particles on HOPG were characterized by ex-situ AFM and XPS analysis, corroborating the latter the formation of a Cd-Ag alloy. Subsequently, the electrodes modified with metallic and bimetallic nanoparticles, and also the substrates free of deposits, were analysed by cyclic voltammetry in solutions containing nitrate ions. It was found that the reduction of nitrate and/or nitrite ions processes begin at more positive potential values in the case of bimetallic deposits, corresponding to a more pronounced catalytic effect by the presence of Cd and Ag, which could be alloyed in the surface, producing a synergistic effect for the reduction of the anions. Even, a change in the catalytic performance by using longer polarization times for the deposition of Cd on supported Ag nanoparticles was verified, that could be related with that alloyed phase. The reaction products were analyzed by colorimetry and ion exchange chromatography for determining nitrate, nitrite and ammonium amounts in solution.

In the synthesis of metallic nanoparticles in microemulsions, we hypothesized that particle size is mainly controlled by the reaction rate. Thus, the changes observed on the particle sizes as reaction conditions, such as concentrations, temperature, type of surfactant used, etc., are varied should not be correlated directly to the modification of those conditions but indirectly to the changes they produce on the reaction rates. By means of time resolved UV-vis spectroscopy, we measured the reaction rates in the production of Pd nanoparticles inside microemulsions at different reactant concentrations, keeping all the other parameters constant. The measured reaction rates were then correlated with the particle sizes measured by transmission electron microscopy (TEM). We found that nanoparticle size increases linearly as the reaction rates increases, independently of the actual reactant concentrations. We proposed that the kinetics is controlled mainly by the diffusion of the reducing agent through the surfactant monolayer covering the microemulsion membrane. With this model, we predicted that particle size should depend indirectly, via the reaction kinetics, on the micelle radius (v0 ~ r^-3), the water volume (v0~vw^3) and the total microemulsion volume (v0~vT^-3), and temperature (Arrhenius). Some of these predictions were explored in this article.

This work set out to explore the influence of kind and surface condition of carbon supports on the electrocatalytic activity of trimetallic PtRuCu alloy nanoparticles. The structure, composition, particle size and catalyst loading were determined by XRD, EDX, XPS, TEM and ICP-AES analysis. XRD studies revealed that support physical characteristics and surface conditions have an important influence in lattice strain, while XPS pointed out that a strong electronic interaction exists between the particles and the carbon support. Electrochemical experiments showed that the activated carbon black supported PtRuCu catalyst exhibits the best performance for methanol and ethanol oxidation and the lowest poisoning rate. The superior catalytic activity of this electrode can be rationalized in terms of metal-support interaction, Pt utilization efficiency and electrical conductivity of the carbon support. Furthermore, the as-prepared electrode exhibits 13 and 7 times higher activity towards methanol and ethanol oxidation when compared with a PtRu/C commercial catalyst.

Ordered mesoporous materials are promising catalyst supports due to their uniform pore size distribution, high specific surface area and pore volume, tunable pore sizes, and long-range ordering of the pore packing. The evaporation-induced self-assembly (EISA) process was applied to synthesize mesoporous mixed oxides, which consist of cobalt ions highly dispersed in an alumina matrix. The characterization of the mesoporous mixed cobalt-aluminum oxides with cobalt loadings in the range from 5 to 15 wt% and calcination temperatures of 673, 973, and 1073 K indicates that Co 2+ is homogeneously distributed in the mesoporous alumina matrix. As a function of the Co loading, different phases are present comprising poorly crystalline alumina and mixed cobalt aluminum oxides of the spinel type. The mixed cobalt-aluminum oxides were applied as catalysts in CO oxidation and turned out to be highly active.

Low loaded Pd/alpha-Al2O3 catalysts (<0.5 wt% Pd) were characterized and tested for CH4 reforming with CO2 at 650 degrees C. The catalysts were prepared by a recharging procedure, using an organometallic precursor, followed by intermediate washing and calcination steps. FTIR spectra of adsorbed CO showed that the Pd surface structure and the particle size were dependent on the number of post-impregnation washing steps. A catalyst sample with a metal dispersion of 33% showing well defined low-index planes (by FTIR) and nearly spherical particles (by TEM) was obtained using two-washing steps. In the reaction, it exhibited a high initial activity followed by a pronounced deactivation due to carbon nanofiber's formation and sintering. TEM analysis of the used catalyst revealed the presence of spherical Pd particles at the end of the fibers that were not attached to the support surface. On the other hand, a high dispersion sample (78%) with a large fraction of Pd atoms with low coordination was obtained by applying three washing steps after impregnation. The presence of small hemispherical particles and larger nearly-flat ones attached to the support were found by TEM. In this case, the catalyst initially showed a very low activity that increased slowly up to a steady value. Although sintering also occurred and the surface structure of the used catalyst resembled the one of the low dispersion catalyst, the amount of carbon formed was quite low. The observed activation under reaction conditions was associated with the slow development of a surface structure that exhibited mainly the (100) plane favoring methane dissociation. However, the initial interaction of the particles with the support suggested by TEM micrographs seems to remain unaltered despite the particle size increase. Consequently, the process of nanofiber's formation and particle separation was inhibited. (C) 2014 Elsevier B.V. All rights reserved.

In this paper, we describe laboratory and classroom exercises designed to obtain the fundamental equation of a rubber band by combining experiments and theory. The procedure shows students how classical thermodynamics formalism can help to obtain empirical equations of state by constraining and guiding in the construction of the physical models for the system under investigation. It also serves as an "experimental" link to statistical thermodynamics models for a rubber band, which is taught to students in more advanced courses. The rubber band system also serves as an example of a "non-ideal" thermodynamics system to introduce a van der Waals-like equation in a context different from gases.

En este trabajo se estudia el efecto de algunos fonones en el cálculo de la estructura de bandas de energía en el modelo de sólido de Kronig-Penney, utilizando para el análisis el programa MathCad 2.5 el cual permite realizar cálculos numéricos y graficación de los resultados en forma sencilla y clara, evitando la necesidad del desarrollo de algoritmos en los lenguajes habituales de programación. Al existir una solución exacta del problema electrónico, es posible realizar una comparación de las bondades de la aproximación de electrones casi libres utilizada en nuestro caso. La introducción heurística de fonones de borde y cuarto de zona de Brillouin en el cálculo permite observar la aparición de bandas prohibidas adicionales, siendo estos resultados interpretados en el marco de la teoría semiclásica de la conducción, permitiendo justificar la calda de ésta debido a la disminución del tamaño de las bandas permitidas. Estos cálculos constituyen un problema de sumo interés y una buena ayuda en el estudio de bandas de energía en cursos avanzados de pregrado y primer curso para graduados en Física del Estado Sólido.

En el presente trabajo analizamos la matriz de transición para el proceso de ionización ión-átomo utilizando la correcta ecuación de Lippmann - Schwinger para describir la interacción de largo alcance del potencial coulombiano. Como resultado de estos cálculos se observa que los procesos de doble colisión pueden ser interpretados a partir del término homogéneo de la ecuación de Lippmann - Schwinger y no se deben al efecto de largo alcance del potencial coulombiano introducido a través de la función de onda eikonal.

A solution stabilization strategy that uses an easily removable media is critical to graphene (G) applications. Here, we demonstrate that highly stable graphene dispersions in low boiling point solvents such as isopropanol can be readily achieved by the uniform deposition of Ag nanoparticles (NPs) on the surface of graphene. Optimizing the synthesis parameters such as ultrasonic intensity, feeding strategy, loading content and precursor concentration allowed us to tune the particle size and, in this way, the stabilizing effects of the NPs on the dispersions. The as-obtained Ag/G/i-PrOH dispersions exhibit versatile nonlinear optical properties suggesting a great potential in nanophotonic applications such as absorber for ultrafast lasers and eye protection.