Gianina Dobrescu

Preparation, characterization and catalytic behavior of Pt-Cu nanoparticles in methane combustion

Abstract Fine and well dispersed Pt-Cu bimetallic nanoparticles stabilized by polyvinyl pyrrolidone (PVP) were synthesized by alkaline polyol method. The molar ratio of Pt to Cu was 1:1. Further, the Pt-Cu bimetallic nanoparticles were supported on alumina and their catalytic behavior in methane combustion was investigated. The as-prepared as well as the supported Pt-Cu nanoparticles were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), fractal analysis and X-ray diffraction (XRD). The dependence of methane combustion on the morphology and surface composition of Pt-Cu nanoparticles was analyzed based on the experimental results.

Dynamic scaling method and interface growth

The dynamic scaling approach is an important tool for describing the time evolution of rough interfaces. It computes dynamic scaling parameters alpha and beta, which characterize surface and time correlations. Applications of dynamic scaling to random deposition and ballistic deposition are discussed. A model of random adsorption on fractal substrates is presented. Then the influence of surface diffusion on adsorption is analyzed. The dependence of alpha and beta on the substrate fractal dimension, together with the dependence of the fractal dimension of the gas-solid interface on adsorption coverage are computed.

Impact of particle size and metal–support interaction on denitration behavior of well-defined Pt–Cu nanoparticles

Well-dispersed Pt–Cu nanoparticles with two average sizes were synthesized: small (≈1.6 nm) and large (≈4.8 nm), respectively. The effects of size and support on the catalytic behavior of the nanoparticles for denitration reaction were analyzed. Both the unsupported and alumina-supported nanoparticles of smaller average size (1.6 nm) were very active, completely converting NO3− and NO2− (an intermediate reaction product) to N2 and NH4+. They were also more selective of N2 compared to the larger particles. The effects of particle size and alumina support on the denitration rate constants were analyzed in detail. The kinetic investigation indicates that the catalytic behavior is strongly related to the size of Pt–Cu nanoparticles as well as to the metal–support interaction. Generally, the larger nanoparticles proved to be less active, but on the other hand, they are less influenced by the support than the smaller ones. The metal–support interaction for bimetallic nanoparticles with smaller average size proved to be a key factor both for nitrate and nitrite reduction. Consideration of the reaction mechanism is made in light of the experimental results.

Fractal dimensions of lanthanum ferrite samples by adsorption isotherm method

Abstract Fractal dimensions of three different samples of lanthanum ferrite were computed using single adsorption method. The fractal Dubinin–Radushkevitch isotherm was used to fit directly the experimental nitrogen adsorption data. Avnir–Jaroniec method for fractal dimension determination was also used. Low and intermediate fractal dimensions were obtained according to BET specific surface areas.

Adhesion AFM Applied to Lipid Monolayers. A Fractal Analysis

Adhesion Atomic Force Microscopy images of lipid monolayers on mica are studied using methods of image processing and fractal analysis. We show that liquid-condensed domains are fractal. Free energy computation indicates that fractal domains have an advantage over circular domains as far as free energy is concerned. This may provide an answer to the question why LC domains are fractal.

Aggregation Behavior of Some Asymmetric Porphyrins versus Basic Biological Tests Response

Fractal analysis of free bases porphyrins was computed on atomic force microscopy (AFM) micrographs using two different methods: the correlation function method and the variable length scale method. The correlation function method provides fractal dimension only for short scale range; results indicate that only few images have fractal properties for short ranges; for the rest of them, no fractal dimension was found using the correlation function method. The variable length scale method occur information for long range scaling. All samples have fractal properties at higher scaling range. For three samples the correlation function method leads to the same fractal dimension as the variable length scale method and scaling ranges for both methods overlap. Results show the necessity to use both methods to describe the fractal properties of AB3  meso-porphyrins that may be used to predict their relative cell localization. In order to emphasize the influence of fractal and textural properties the results regarding their self-similarity and texture/morphology were further compared with their behavior in biological assessment, that is, functionality of some Jurkat cell lines.

SIMULATION OF CO CHEMISORPTION ON Pt SUPPORTED ON FRACTAL SURFACES

CO chemisorption on Pt supported on fractal surfaces was simulated in order to compute chemisorption dimension and active sites fractal dimension. Pt deposition was simulated using different models on both fractal and planar surfaces. The potential energy surface with two adsorption positions model was used to compute Pt–CO interaction and a Lennard–Jones 6–12 potential was used to simulate CO–CO interaction. Two Pt phases on fractal surface, one at low concentration — the dispersed phase and the second at high concentration — the aggregated phase characterized by weak interactions with support are obtained. The results are in accord with experimental data of CO chemisorption on Pt supported on γ-alumina. Computed data obtained for planar support are compared with those obtained on fractal support. The effect of fractal support on chemisorption data is underlined.