Search

Diffuse reflectance IR spectra of CO adsorbed on Pt/Mg(Al)O catalysts were studied at room temperature and different surface coverages of metallic Pt. They show the existence of two types of metallic Pt particles. One type has a normal behavior toward the adsorption of CO, which is probably related to the lower dispersion of Pt. The other type probably corresponds to smaller negatively charged clusters like those found for Pt-loaded alkaline and alkaline-earth forms of zeolites. They are characterized by the very low frequency of the singletone corresponding to the linear form of adsorbed CO and high thermal stability of the bridging complexes of CO with metallic Pt. Such by metal-support interaction modified platinum is likely responsible for high activity and selectivity of Pt/Mg(Al)O catalyst inn-alkanes aromatization.

International audience; Methyl viologen (MV2+) initially exchanged in a zeolite Y modified carbon paste electrode (ZMCPE) is reduced after being exchanged for the supporting electrolyte cation. The use of an electrolyte cation that cannot enter zeolite channels to a great extent does not give rise to appreciable currents while a non‐size‐excluded cation allows liberating MV2+ from zeolite particles and their subsequent reduction at the electrode–solution interface. Following those observations, the MV2+‐based ZMCPE has been used for the constant potential (−0.85 V) amperometric detection of nonreducible:, non‐size‐excluded cations in aqueous medium. The performance of this electrode was investigated in both batch injection analysis (BIA) and flow injection analysis (FIA). The great advantage of BIA coupled to the amperometric detection is the ability to use electrolyte‐free sample solutions. For FIA experiments, dissolved oxygen was eliminated by using an electrochemical scrubber containing porous carbon electrodes. With the MV2+‐doped ZMCPE, alkali and alkali‐metal cations can be detected at the submillimolar level for both batch and flow injection analysis.

The location of iron in five deferrated soil kaolinites and several reference samples has been investigated using chemical analyses, acid dissolution and electron paramagnetic resonance spectroscopy.The iron of most of the kaolinites can be divided into a 'structural iron' content, measured by the amount of iron, dissolved at the same rate as aluminium by acid attack, and a 'resistant iron' content, which is concentrated with the residues.Integration of the geff~4 resonance bands of the electron paramagnetic resonance (EPR) spectra allows a semiquantitative estimate of the 'structural iron' in the samples. A multiple relationship seems to exist between the crystallinity index, the 'structural iron' content and the shape and intensity of both geff~4 and geff~2 EPR signals. The tropical soil kaolinites are a peculiar category with a high content of iron (>2% structural Fe2O3) fire-clay kaolinite, low crystallinity and a specific EPR spectrum exhibiting strong geff~4 resonance bands and no or weak geff~2 sharp doublet.

When MgO powders are impregnated with copper ions dissolved in water, hydrolysis to Mg(OH) 2 takes place. Following decomposition of the latter, considerable loss of surface area occurs with incorporation of Cu 2+ ions in the bulk of MgO, as revealed by ESR spectra. Impregnation with Cu 2+ ions dissolved in organic solvents decreases the amount of Cu 2+ ions incorporated into the bulk of MgO. These observations lead to a method of preparation of high surface area MgO powders with Cu 2+ ions at their surface.

Adsorption, binding, behavior and decomposition of Ni(CO)4 and Fe(CO)5 on zeolites and alumina have been investigated using 13C-NMR spectroscopy. Their decompositions result in highly dispersed metallic particles. The nickel tetracarbonyl, which can be easily distorted, interacts more strongly with the various surfaces and this interaction increases with increasing acidity. During the thermal decomposition of Fe(CO)5, a small (4 ppm) low field shift of these precursors was observed, while a large (−9 ppm) high field shift is characteristic of the photochemical decomposition. These results can be explained unambiguously by more charge transfer to the surface in the photochemical decomposition. The re adsorption of CO stopped at Fe(CO) at room temperature which demonstrates clearly the monodispersed nature of the iron atoms.