Bernard Claudel

Catalysis of carbon monoxide oxidation by cerium dioxide: II. Microcalorimetric investigation of adsorption and catalysis

Abstract Adsorption and catalytic properties of ceria surfaces towards carbon monoxide oxidation have been investigated by microcalorimetry. Results are interpreted assuming that the defect structure of the catalyst is single-phased, and that its catalytic action consists of successive oxidations and reductions of its surface.

Catalysis of carbon monoxide oxidation by cerium dioxide: I. Correlations between catalytic activity and electrical conductivity

A mechanism involving the oxidation and reduction of the solid is presented for carbon monoxide oxidation on cerium dioxide. Expressions for the reaction rate and the electrical conductivity of the catalyst are derived from this mechanism. Experiments have been performed in which these two quantities have been simultaneously recorded. The results agree with the proposed mechanism.

ESR study of CO adsorption on thoria

Abstract Electron spin resonance (ESR) study of 12 CO and 13 CO adsorbed on thoria between 25 and 300 °C shows that part of the adsorbate exists in the form of a paramagnetic axial radical, the unpaired electron of which is located in a π orbital. Two types of adsorbed CO are detected by ESR, for which the unpaired electron is, respectively, 33 and 15% on the carbon atom. These observations are consistent with the previous hypothesis of a positively charged CO adsorbate on thoria.

Catalytic properties of thorium oxide in the oxidation of carbon monoxide: I. Calorimetric confirmations of adsorption and catalysis processes

Abstract Adsorptive and catalytic properties of thoria have been reexamined in the light of some new microcalorimetric experiments. It has been shown that oxygen can be weakly adsorbed under a neutral form, that chemisorption heat of carbon monoxide on n -type thoria linearly decreases with the logarithm of the adsorbed volume, and that carbon dioxide is chemisorbed under two forms, one of which is an intermediary in carbon monoxide oxidation, the other one being an inhibitor of this catalysis.

Temperature-programmed desorption and photoluminescence studies of thorium dioxide surface states

Abstract An apparatus was built which allowed us to prepare thoria surfaces in a high vacuum (≈10 −8 Torr), to treat them in the presence of various gases, to analyze the gases desorbed at increasing temperatures, and to record photoluminescence spectra in various ambient conditions. Attention has been focused on the species responsible for the observed bands in the excitation and emission spectra. It is supposed that two of them are constituted by anionic vacancies, in the bulk and at the surface, and the third by surface OH groups. This ascription is confirmed by doping thoria with uranium, and allows us to propose a surface model consistent not only with the presently reported investigations, but also with the previously reported catalytic properties of thoria.

A new uranium compound: The sodium uranyl formate monohydrate

Abstract A new uranium compound, NaUO 2 (HCOO) 3 , H 2 O has been prepared and investigated by X-ray diffraction and infrared absorption. It crystallizes in the monoclinic system, the unit cell parameters being: a = 6·741 A ; b = 24·43 A ; c = 6·332 A ; β = 117·63° . An idealized structure is proposed for this compound.

Spectres de luminescence des diformiates d'uranyle monohydraté et anhydre en phase solide

Abstract Luminescence spectra of uranyl formate monohydrate and anhydrous uranyl formate have been recorded at room temperature and at 77°K. Observed bands have been interpreted by means of the frequency of the transition from the first electronically excited state to the ground state of uranyl ion and certain characteristic frequencies of the latter ion and of other constituents of the crystal.

Catalytic properties of non-stoichiometric uranium-thorium mixed oxides in carbon monoxide oxidation

Abstract Non-stoichiometric uranium-thorium mixed oxides, of general formula UxTh1 − xO2 + y, have an important catalytic activity in carbon monoxide oxidation between 250 and 350 °C. Kinetic study of the reaction is consistent with a mechanism based on oxido-reduction of the catalysts surface. A detailed reaction pattern is proposed and discussed, where oxygen interstitial atoms play the essential role.

Electron spin resonance study of oxygen adsorption on thorium oxide

Oxygen O–2 species are formed during oxygen adsorption on thorium dioxide surfaces, in the presence of carbon monoxide or hydrogen adsorbates. The kinetics of the formation of O–2 species at 298 K have been followed.

Chemiluminescence during catalysis. Part 2.—Luminescent transitions of some rare-earth activators embedded in the catalyst lattice

A novel “cataluminescent” effect is described in which rare earth activators introduced into the catalyst thoria are electronically excited during carbon monoxide oxidation and emit a light very similar to that given by photoluminescence.