Adsorption of probe molecules in pillared interlayered clays: experiment and computer simulation.

In this paper we investigate the adsorption of various probe molecules in order to characterize the porous structure of a series of pillared interlayered clays (PILC). To that aim, volumetric and microcalorimetric adsorption experiments were performed on various Zr PILC samples using nitrogen, toluene, and mesitylene as probe molecules. For one of the samples, neutron scattering experiments were also performed using toluene as adsorbate. Various structural models are proposed and tested by means of a comprehensive computer simulation study, using both geometric and percolation analysis in combination with Grand Canonical Monte Carlo simulations in order to model the volumetric and microcalorimetric isotherms. On the basis of this analysis, we propose a series of structural models that aim at accounting for the adsorption experimental behavior, and make possible a microscopic interpretation of the role played by the different interactions and steric effects in the adsorption processes in these rather complex disordered microporous systems.

Topological considerations on microporous adsorption processes in simple models for pillared interlayered clays.

The microporous structure of pillared interlayered clays is determined by their interlayer separation and the distribution of the pillars that separate their layers. The pillars provide stability to these quasi-two-dimensional high surface area materials. In this work we present a topological analysis of available and accessible volumes within various simple models of pillared interlayered clays. Each model is characterized by a distribution of pillars. Both fully ordered structures and disordered pillar distributions with either attractive or repulsive interpillar correlations are considered. Particular attention is paid to the problem of accessibility. In systems with similar degrees of porosity, even when cavities within each model might be able to host the same adsorbate molecules, their accessibility will strongly depend on the pillar distribution. The theoretical analysis presented in this work may facilitate the interpretation of experimental results, pointing out those quantities that are key to describe the texture of the porous material.

XPS and 1H NMR study of thermally stabilized Rh/CeO2 catalysts submitted to reduction/oxidation treatments.

Rh/CeO2 catalysts submitted to different H2 reduction, Ar+ sputtering, and oxidation treatments have been studied by X-ray photoelectron (XPS) and 1H nuclear magnetic resonance (NMR) spectroscopies. Depending on the reduction temperature, two stages have been identified in the reduction of the catalyst: below 473 K, reduction increases the amount of OH and Ce3+ species; above this temperature, reduction produces oxygen vacancies at the surface of the support. Volumetric and microcalorimetric techniques have been used to study hydrogen adsorption on the catalyst, and 1H NMR spectroscopy was used to differentiate hydrogen adsorbed on the metal from that adsorbed on the support. From 1H NMR and TEM results, the main metal particle size (38 A) in the Rh/CeO2 catalyst has been estimated. The influence of the support reduction on the metal adsorption capacity has also been investigated, showing that formation of oxygen vacancies at the metal-support interface enhances the electronic perturbation and decreases the hydrogen adsorption on metal particles. The comparison of data reported on catalysts of high and low surface area supports has shown that both processes are shifted to higher temperatures in the Rh/CeO2 catalyst of lower surface area.