Ricardo Oliva

Synthesis and properties of PdSn/Al2O3 and PdSn/SiO2 prepared by solvated metal atom dispersed method

A series of solvated metal atom dispersion (SMAD) catalysts: Pd/SiO2, Pd/Al2O3, Sn/SiO2, Sn/Al2O3 ,P d x Sny /SiO2 and Pdx Sny /Al2O3. It was prepared by simultaneous evaporation of Pd and Sn. The metals were co-deposited at 77 K using acetone, 2-propanol and THF to produce colloids “in situ” all the supported catalyst were characterized by chemisorption, transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and TPR. This series of catalyst were tested for crotonaldehyde hydrogenation in gas phase to obtain crotyl alcohol.

Influence of the thermal annealing on the electrical resistivity and thermal diffusivity of Pd:Ag nanocomposites

In this paper, we report on the influence of thermal annealing on the electrical and thermal properties of nano-clustered Pd:Ag particles packed into compressed thin wafers. The nano-crystalline Pd:Ag compacts were prepared by solvent evaporation of non-aqueous metal colloids prepared by clustering of metal atoms in organic solvents at low temperature. Samples of Pd:Ag nano-clustered powder so obtained were then compressed into roughly 250 μm thick, 10 mm diameter wafers, and annealed at different temperatures, for about 1 h. The dependence of the electrical resistivity and of the thermal diffusivity of the resulting compacts on their corresponding annealing temperatures were investigated using a LCR impedance meter and a photoacoustic thermal diffusivity measurement apparatus.

SYNTHESIS AND TEM STUDIES OF GALLIUM COLLOIDS PREPARED IN NONAQUEOUS SOLVENTS

In this work metallic colloidal dispersions were obtained by simultaneous co-condensation of gallium atoms with organic solvents at 77 K. The atoms were produced by resistive heating and were reacted with ethanol, 2-propanol, 2-methoxyethanol, acetone and 2-butanone to produce colloids. The kinetic stability of colloid dispersions was related to the solvation effect of organic molecules, e.g. low stability for ketones and higher stability for 2-propanol colloids. The electrophoretic measurements reveal that particles are negatively charged being 5.1 V for 2-propanol and 0.5 V for 2-butanone. The colloids of Ga-2-propanol and Ga-2-methoxyethanol exhibit an absorption band at 213 and 209 nm, respectively. The transmission electron microscopy studies reveals an average particle size distribution ranging from 1.0 to 1.2 mm depending on the solvent. Most of the colloids exhibit a spherical shape with some degree of agglomeration. The electron diffraction of Ga-colloids shows the presence of a mixture of Ga and Ga2O3 particles. After solvent evaporation, amorphous active powders were obtained. The solids were analyzed by thermogravimetry being Ga-2-methoxyethanol the most stable with a decomposition temperature of 308° C. The Ga-acetone shows two decomposition decays at 98 and 223° C, respectively. Similar behavior was obtained with 2-butanone. The FT-IR confirms the presence of the solvent in the powders. In the case of Ga-acetone and Ga-2-butanone a n C=O at 1728 cm-1 reveals the solvent incorporation in the active solids.

Colloids and amorphous solids of Pr, Yb, and Er using 2-propanol and 2-butanone

Abstract Nonaqueous ytterbium, praseodymium, and erbium colloids and fine powders were prepared by cocondensation of the metals with 2-propanol and 2-butanone at 77 K. Films were formed from a mixture of the metals and metal oxides, and contained a certain amount of solvent. The powder X-ray diffraction patterns correspond to the respective lanthanide oxides. A complete characterization study by infrared spectroscopy was carried out to determine the presence of solvent in the amorphous films. The stability of the colloids and amorphous films at room temperature was measured. In addition, their stability in the presence of water moisture and oxygen was studied. Thermogravimetric studies showed that the films were stable up to 250°C, and the remnant solvent incorporated into them was degraded by 500°C. TGA-FTIR results indicate a self-catalysis process in which 2-propanol is oxidized by Yb, Er, and Pr to form carbonyl compounds. The morphologies of the films were studied by scanning electron microscopy. The shape and surface characteristics observed depended on the metal surface (copper or aluminum) used.

Photoacoustic assessment of oscillations in water vapor desorption from nanostructured catalytic surfaces

Abstract In this Letter, we report on the short and long term dynamical behavior of water vapor sorption–desorption cycling on catalytic active nanoclustered Pd:Ag particles packed into compressed thin wafers. The water vapor desorption kinetics, following a hydration session, was monitored using conventional photoacoustic (PA) detection and relative humidity monitoring. It was found that the dehydration process was always accompanied by oscillations, with a period of the order of minutes. These observations are tentatively explained in terms of a PA model appropriate for damp porous materials in which we incorporated a term to describe these oscillations as arising from a competition between reactive sorption processes on the Pd:Ag surface.

Thermal analysis of organocopper and organotin metal films. Part 8

Abstract The thermal stabilities of copper and tin films containing various organic solvents have been studied by thermogravimetry (TG) between 298 and 823 K under a flow of nitrogen. The thermal stabilities of the Cu films decrease in the order Cu-THF > Cu-DMF > Cu-toluene > Cu-ethanol > Cu-acetone > Cu-2-butanone > Cu-benzene, Cu-2-propanol > Cu-DMSO. On the other hand, the organotin films exhibit a decreasing stability in the following order: Sn-2-propanol > Sn-ethanol > Sn-acetone > Sn-2-butanone, > Sn-benzene > Sn-DMF, Sn-DMSO > Sn-toluene. This suggests that the solvent incorporated into the film has a considerable influence on the stability, in that solvents containing oxygen are very stable and have a comparatively high thermal decomposition temperature (T d ) and low residual weight. The order of the thermal decomposition reaction was found to be zero in most of the cases. The pre-exponential factor and the activation energy of the decomposition of Cu and Sn metal films are also compared.