Correlated site-bond ensembles: Statistical equilibrium and finite size effects

This work presents a Monte Carlo analysis of the propagation of correlation strength in site-bond square lattices generated through the dual site-bond model (DSBM), where the values of the property assigned to sites and bonds are sampled from two uniform density distributions that may have some overlapping area with each other. Correlations appear when a construction principle is established. Although this model has been extensively used in many physical applications, such as adsorption and surface diffusion on heterogeneous surfaces and percolation and transport processes in porous media, a careful study of the way correlated topology is settled on through the system was lacking. The dependence of the relaxation time needed to reach equilibrium and of the minimum size of the network to be used is established for different correlation strengths, represented by the overlapping parameter Ω. A more accurate empirical equation, relating the characteristic correlation length l0, corresponding to the spatial correlation function, and Ω, is found, than the one used in former applications of the DSBM.Fil: López, Raúl Horacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich". Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich"; ArgentinaFil: Vidales, Ana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich". Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich"; ArgentinaFil: Zgrablich, Giorgio. Universidad Nacional de San Luis; Argentin

A Study of the Adsorption Properties of Single Walled Carbon Nanotubes Treated with Nitric Acid

The changes observed in the properties of Single Walled Carbon Nanotubes (SWCNTs) after treatment with nitric acid are reported. The oxidized nanotube samples were characterized morphologically by scanning electron microscopy and structurally by Raman spectroscopy, thermogravimetric analysis, infrared spectroscopy and X-ray photoelectron spectroscopy. Gas adsorption was used to study the changes in the surface properties of the samples (including the changes in their porosity), as well as the changes in the adsorbate–adsorbent interactions which occurred as a result of the acid treatment. The adsorption studies were conducted using nitrogen at 77 K and CO2 at different temperatures between 263 K and 289 K at sub-atmospheric pressures. The isosteric heat was calculated from the data obtained and indicated a higher adsorbate–adsorbent interaction for the oxidized materials. A correlation was found between morphological and structural evolution and the adsorption properties of CO2, a probe gas which appears to be very suitable for characterizing the microporosity of these kinds of materials.Fil: Garcia Blanco, Andres Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich". Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich"; ArgentinaFil: Villarroel Rocha, Jhonny. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich". Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich"; ArgentinaFil: Múnera Agudelo, John Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; ArgentinaFil: Nazzarro, Marcelo Sandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich". Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich"; ArgentinaFil: Zgrablich, Giorgio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich". Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich"; ArgentinaFil: Sapag, Manuel Karim. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich". Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich"; Argentin

Monte carlo simulation strategies for predicting CO 2/CH 4 adsorption onto activated carbons from pure gas isotherms

The problem of predicting the adsorptive properties of activated carbon (AC) towards a mixture of gases from the simple knowledge of the adsorption properties of the pure components is addressed, with special reference to the CO2/CH4 mixture. The adsorption process for the pure gases and their mixtures was simulated using the Grand Canonical Monte Carlo (GCMC) method and the calculations were then used to analyze experimental isotherms for the pure gases and for mixtures with different molar fractions in the gaseous phase. It was shown that the pore-size distributions (PSDs) “sensed” by each of the pure probe gases was different one from the other and also from the PSDs “seen” by the mixture. A mixing rule for combining the PSDs corresponding to the pure gases is proposed for obtaining predictions regarding the adsorption of the corresponding mixtures, which are then compared with those arising from the classical IAST approximation. For this purpose, selectivity curves for CO2 relative to CH4 have been calculated and compared with experimental values. It was concluded that, for the adsorbate/adsorbent system under study, the proposed GCMC mixed model was capable of predicting the binary adsorption equilibrium, and especially the selectivity, more accurately than the IAST.Fil: de Oliveira, José C. A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Luis. Instituto de Física Aplicada; Argentina. Universidad Nacional de San Luis; ArgentinaFil: Rios, Rafael B.. Universidade Federal do Ceará; BrasilFil: López, Raúl Horacio. Universidad Nacional de San Luis; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Luis. Instituto de Física Aplicada; ArgentinaFil: Peixoto, Hugo R.. Universidade Federal do Ceará; BrasilFil: Cornette, Valeria Cecilia. Universidad Nacional de San Luis; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Luis. Instituto de Física Aplicada; ArgentinaFil: Torres, A. Eurico B.. Universidade Federal do Ceará; BrasilFil: Calvalcante Jr., Célio L.. Universidade Federal do Ceará; BrasilFil: Zgrablich, Jorge Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Luis. Instituto de Física Aplicada; Argentina. Universidad Nacional de San Luis; Argentin

Efecto de la heterogeneidad sobre las isotermas de adsorción de carbones activados

Los carbones activados (CA) son materiales microporosos que poseen gran capacidad de adsorción. La heterogeneidad de cualquier adsorbente, en particular la de los CA, puede ser separada en dos grandes familias: energética (o superficial) y estructural. La heterogeneidad estructural es causada por la presencia de poros de diferentes tamaños y formas, y por su posible interconexión; mientras que la heterogeneidad energética se origina por las irregularidades superficiales, así como por la presencia de grupos funcionales y/o impurezas. En este trabajo se discutirán diferentes modelos de heterogeneidad superficial en materiales con poros de geometría, tipo placas paralelas, y su efecto sobre las isotermas de adsorción y en las distribuciones de tamaño de poros

Determination of the pore size distribution of correlated mesoporous networks

In the present work we study how the adsorption desorption hysteresis loop of a mesoporous disordered medium represented by a 3-dimensional Dual Site-Bond Model (DSBM) is affected by percolation. Site and bond distributions are assumed to be gaussians. The behavior of the threshold pressure for the evaporation processe suggests a method to determine the site and bond distributions from experimental adsorption-desorption hysteresis curves. Traditional methods developed for non-correlated networks are tested and evaluated against our simulation results showing the discrepancy mainly for highly correlated networks. Results of the prediction capability of our method are shown.Fil: López, Raúl Horacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich". Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich"; ArgentinaFil: Vidales, Ana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich". Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich"; ArgentinaFil: Zgrablich, Giorgio. Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Departamento de Física; Argentin

Percolation Effects on Adsorption-Desorption Hysteresis

In the present work we study how the adsorption−desorption hysteresis loop of a mesoporous-disordered medium represented by a three-dimensional dual site-bond model is affected by percolation for different kinds of site and bond distributions. The behavior of the threshold pressure for the evaporation process, as a function of the separation between the site and bond distributions and their dispersions, suggests a method to determine them from experimental adsorption−desorption hysteresis curves.Fil: López, Raúl Horacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich". Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich"; Argentina. Universidad Nacional de San Luis. Facultad de Ciencias Fisico Matematicas y Naturales. Departamento de Fisica. Laboratorio de Ciencias de Superficies y Medios Porosos; ArgentinaFil: Vidales, Ana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich". Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich"; Argentina. Universidad Nacional de San Luis. Facultad de Ciencias Fisico Matematicas y Naturales. Departamento de Fisica. Laboratorio de Ciencias de Superficies y Medios Porosos; ArgentinaFil: Zgrablich, Giorgio. Universidad Nacional de San Luis. Facultad de Ciencias Fisico Matematicas y Naturales. Departamento de Fisica. Laboratorio de Ciencias de Superficies y Medios Porosos; Argentin

Toward the study of catalytic reactions under industrial conditions: A contaminated CO oxidation model

Recent trends in surface chemistry are trying to bridge the gap between ideal ultrahigh vacuum (UHV) studies and results of catalytic reactions under industrial conditions. These conditions are mainly characterized by a heterogeneous active phase, high pressure and the presence of contaminant species. In the present work we address the last of these three factors. More precisely we study the effects of a contaminating species, whose only action is adsorption and desorption being otherwise inert, on the kinetics of CO oxidation on transition metals. We introduce a suitably modified Ziff-Gulari-Barshad model, a contaminated ZGB model, and obtain by Monte Carlo simulations the behavior of the steady state of the system for different CO and contaminant concentrations. We find that the reaction window shrinks with increasing contaminant concentration until it disappears at a critical value. Moreover, we find that the classical lower bound ZGB irreversible phase transition is unaffected while the upper bound first order transition transforms continuously into a second order one with increasing contaminant concentration, as revealed by the behavior of critical exponents.Fil: Bustos Giunta, Victor Angel. Universidad Nacional de San Luis. Facultad de Ciencias Fisico Matematicas y Naturales. Departamento de Fisica. Laboratorio de Ciencias de Superficies y Medios Porosos; ArgentinaFil: Uñac, Rodolfo Omar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich". Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich"; Argentina. Universidad Nacional de San Luis. Facultad de Ciencias Fisico Matematicas y Naturales. Departamento de Fisica. Laboratorio de Ciencias de Superficies y Medios Porosos; ArgentinaFil: Zgrablich, Giorgio. Universidad Nacional de San Luis. Facultad de Ciencias Fisico Matematicas y Naturales. Departamento de Fisica. Laboratorio de Ciencias de Superficies y Medios Porosos; Argentin

Mechanistic and Experimental Aspects of the Structural Characterization of Some Model and Real Systems by Nitrogen Sorption and Mercury Porosimetry

Several mechanistic and phenomenological aspects of mercury intrusion and nitrogen sorption processes involving some model and real mesoporous systems were studied. The experimental pore systems examined consisted of two substrates: (a) a globular solid composed of monodisperse silica spheres in a perfect rhombohedral arrangement and (b) a controlled pore glass solid. Comparisons between the experimental nitrogen sorption and mercury porosimetry pore-size distributions demonstrated: (i) the existence of several mechanistic effects responsible of irreversible capillary behaviour that influences the calculation of pore structure parameters; (ii) the choice of the right sorption process (i.e. condensation or evaporation) suitable for comparison with either intrusion or extrusion results; (iii) the types of porous structures capable of convenient pore-size characterization by either nitrogen sorption and/or mercury porosimetry methods; and (iv) the nature of the pore entities (i.e. chambers or necks) that control the incumbent capillary process

Lattice gas study of the kinetics of the NO-CO catalytic reaction on Pd nanoclusters

The kinetics of the NO-CO reaction on Pd nanoclusters is studied through a lattice-gas model and Monte Carlo simulation. Pd nanoclusters with three typical sizes: 2.8 nm, 6.9 nm and 15.6 nm, are considered. These nanoclusters have been epitaxially grown on MgO(100) and tested for the NO-CO reaction in previous experimental work [ref. 9-11: C. H. F. Peden, D. W. Goodman, D. S. Blair, P. J. Berlowitz, G. B. Fisher and S. H. Oh, J. Phys. Chem., 1988, 92, 1563; C. Duriez, C. R. Henry and C. Chapon, Surf. Sci., 1991, 253, 190; L. Piccolo and C. R. Henry, Appl. Surf. Sci., 2000, 162-163, 670], thus providing the motivation for the present study. According to their size, the nanoclusters present different proportions of Pd(100) and Pd(111) facets. The effects of CO and NO desorption are found to be of fundamental importance for the behavior of the system. In all cases the medium size particles are found to be the most active. At low temperature, where NO desorption can be neglected (since the activation energy for desorption of NO on Pd is about 5 kcal mol-1 greater than that for the desorption of CO), the largest particles are revealed as the less active, while at high temperature, where both NO and CO desorption take place, the smallest particles are found to be the less active. These results are in concordance with the experimentally observed behavior.Fil: Bustos Giunta, Victor Angel. Universidad Nacional de San Luis; ArgentinaFil: Uñac, Rodolfo Omar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich". Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich"; ArgentinaFil: Zgrablich, Giorgio. Universidad Autónoma Metropolitana; MéxicoFil: Henry, Claude R.. Centre National de la Recherche Scientifique; Franci

Energetic topography in adsorption onto heterogeneous surfaces

The adsorption of gases onto heterogeneous surfaces has been reviewed, highlighting models capable of taking energetic topography effects into account. The basic ideas are contained in the fundamental Generalized Gaussian Model (GGM) developed to represent mobile adsorption onto heterogeneous surfaces at low coverage, where the energetic topography is considered through an adsorptive energy distribution with a spatial correlation function. Adsorbate molecules interact amongst them via Lennard-Jones interactions. Model predictions have been compared to Monte Carlo simulations of adsorption onto heterogeneous solids obtained by doping a pure crystalline solid with different concentrations of impurities. Energetic topography effects were shown to be important, being predicted correctly by the model at low coverage. In addition, a simplified patchwise model was also considered. The adsorption of particles with nearest-neighbour attractive and repulsive interactions was studied using Monte Carlo simulation on bivariant surfaces characterized by patches of weak and strong adsorbing sites of size "i". Patches were considered to have either a square or a strip geometry, arranged either in a deterministic ordered structure or in a random way. Quantities have been identified which scale obeying power laws as a function of the scale length "l". The consequences of this finding for the determination of the energetic topography of a surface from adsorption measurements were discussed.Fil: Ramirez Pastor, Antonio Jose. Universidad Nacional de San Luis. Facultad de Ciencias Fisico Matematicas y Naturales. Departamento de Fisica. Laboratorio de Ciencias de Superficies y Medios Porosos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich". Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich"; ArgentinaFil: Bulnes, Fernando Manuel. Universidad Nacional de San Luis. Facultad de Ciencias Fisico Matematicas y Naturales. Departamento de Fisica. Laboratorio de Ciencias de Superficies y Medios Porosos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich". Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich"; ArgentinaFil: Nazzarro, Marcelo Sandro. Universidad Nacional de San Luis. Facultad de Ciencias Fisico Matematicas y Naturales. Departamento de Fisica. Laboratorio de Ciencias de Superficies y Medios Porosos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich". Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich"; ArgentinaFil: Riccardo, Jose Luis. Universidad Nacional de San Luis. Facultad de Ciencias Fisico Matematicas y Naturales. Departamento de Fisica. Laboratorio de Ciencias de Superficies y Medios Porosos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich". Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich"; ArgentinaFil: Zgrablich, Giorgio. Universidad Nacional de San Luis. Facultad de Ciencias Fisico Matematicas y Naturales. Departamento de Fisica. Laboratorio de Ciencias de Superficies y Medios Porosos; Argentin