Low-temperature destruction of carbon tetrachloride over lanthanide oxide-based catalysts: from destructive adsorption to a catalytic reaction cycle.
Van der Avert, Pietera; Podkolzin, Simon G.c; Manoilova, Olgab; De Winne, Hendrika; Weckhuysen, Bert M.a,b
Chemistry-A European Journal 10(7), 1637-1646 (2004)
The catalytic destruction of carbon tetrachloride in the presence of steam, CCl4 + 2 H2O ® 4 HCl + CO2, was investigated at 200-350°C over a series of lanthanide (La, Ce, Pr and Nd) and alkaline earth (Mg, Ca, Sr and Ba) oxide-based catalysts with kinetic experiments, Raman spectroscopy, X-ray photoelectron spectroscopy, infrared spectroscopy, X-ray diffraction and density functional theory calculations. This new catalytic chemistry was achieved by combining destructive adsorption of CCl4 on a basic oxide surface and concurrent dechlorination of the formed partially chlorinated solid by steam. The combination of the two non-catalytic reactions into a catalytic cycle provided a rare opportunity in heterogeneous catalysis for studying the nature and extent of surface participation in the overall reaction chemistry. The reaction is proposed to proceed over a terminal lattice oxygen site with a step-wise donation of chlorine atoms from the hydrocarbon to the surface and with the formation of the gas-phase COCl2 intermediate, which readily re-adsorbs at the catalyst surface to form CO2. In a second step, the active catalyst surface is regenerated with steam with the formation of gas-phase HCl. Depending on the reaction conditions, the catalytic material was found to transform dynamically from the metal oxide state to the metal oxide chloride or metal chloride states due to the bulk diffusion of oxygen and chlorine atoms. A catalyst obtained from a 10 wt % La2O3/Al2O3 precursor exhibited the highest destruction capacity: 0.289 g CCl4.h-1.g-1 catalyst at 350°C, which is higher than activities for any other reported catalytic system.
[a] Centrum voor Oppervlaktechemie en Katalyse Departement Interfasechemie, KULeuven Kasteelpark Arenberg 23, 3001 Leuven, Belgium)
[b] Departement Anorganische Chemie en Katalyse, Debye Instituut, Universiteit Utrecht, Sorbonnelaan 16, 3584 CA Utrecht, The Netherlands
[c] The Dow Chemical Company, Corporate Research, Midland, MI 48674, USA
Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim
CODEN: CEUJED, ISSN: 0947-6539, CAN 141:41964, AN 2004:320610