L. Faure

Chemiluminescence during the catalysis of carbon monoxide oxidation on a thoria surface

It is shown that the catalysis of carbon monoxide oxidation on a thoria surface treated in oxygen and in vacuo is accompanied by a specific luminescence. The luminous intensity is proportional to the catalysis rate and its spectral composition is different from that of oxygen adsorboluminescence on the same surface. When the thoria surface has undergone a pretreatment with hydrogen, this chemiluminescence is no longer observed. These results are interpreted in view of previous findings concerning the catalytic mechanism, and explained by the emission of light due to the annihilation of an exciton formed during the reaction of neighboring CO+ and O− species.

On the “immobilization” of titanium dioxide in the photocatalytic oxidation of spent waters

The problems raised by the immobilization (or anchoring) of a photocatalyst, namely TiO2, on a support are reviewed, from the standpoints of the procedure itself and of the structure, adherence, morphology and photocatalytic activity of the deposit. Some new experimental findings are also reported. It is concluded that the immobilized photocatalyst absorbs all the actinic light that it can, but the immobilization treatment generally lowers its activity. It would therefore be advisable to tailor a treatment which would at least maintain this activity, and even increase it, possibly by size quantization.

The photo-oxidation of acetic acid by oxygen in the presence of titanium dioxide and dissolved copper ions

Abstract Acetic acid is oxidized by oxygen in the presence of UV light, TiO2 and dissolved copper ions being the catalysis. The reaction rate is zeroth order with respect both to acetic acid and to dissolved oxygen, and is proportional to the absorbed light intensity, with a quantum yield of 0.06. The variation in reaction rate with the concentrations of the different copper species present in the solution, i.e. free ions, Cu(CH3COO)+ and Cu(CH3COO)2, leads us to propose the second of these as the reactive species adsorbed on the TiO2 surface, the diacetato complex (or neutral salt) also being adsorbed on the TiO2 surface, but as a poison. These results extend those already obtained for formic acid and are a part of a general scheme of photo-oxidation of carboxylic acids in the presence of these catalysts.

PHOTO-OXIDATION OF FORMIC ACID BY OXYGEN IN THE PRESENCE OF TITANIUM DIOXIDE AND DISSOLVED COPPER IONS: OXYGEN TRANSFER AND REACTION KINETICS

Photocatalytic activity of TiO2 in the oxidation by oxygen of formic acid is considerably enhanced by the presence of dissolved copper ions. The role of oxygen transfer between the gas phase and the slurry is examined. The kinetic results obtained in the absence of mass transfer limitations lead to a mechanism based upon a redox cycle between Cu2+ and Cu+ species adsorbed on the surface of TiO2.

The photo-oxidation of propionic acid by oxygen in the presence of TiO2 and dissolved copper ions

Abstract The photo-oxidation of propionic acid by oxygen in aqueous solution has been studied in the presence of TiO 2 and dissolved copper ions as catalyst. The kinetics results agree with a “rake scheme” which involves acetic acid as an intermediate between propionic acid and the final product CO 2 . The role in this scheme of carboxylato complexes of copper both in the dissolved state and in the adsorbed state is stressed.

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.

Photo-oxidation of dissolved formic acid by gaseous oxygen in the presence of iron ions

Abstract The kinetic study of the reaction: HCOOH + 1 2 O2 → CO2 + H2O photocatalyzed by iron ions has been undertaken. Its results are consistent with the occurrence of a redox cycle: These two stoichiometric equations represent, in both cases, a complex mechanism which has tentatively been put forward. Such photocatalytic reactions could be invoked m the natural purification of polluted waters.

Infrared spectrophotometry study of hydrogen interaction with carbonates adsorbed on ThO2

Observations from this study lead to the following mechanism for the CO/sub 2/ methanation on ThO/sub 2/: CO/sub 2/ (adsorbed as a carbonate on ThO/sub 2/) is first reduced to CO by hydrogen, CO being manifested on the surface as a formate; hydrogenation of CO in a later stage than leads exclusively to methane.

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.