BENZENE HYDROGENATION AS A TOOL FOR THE DETERMINATION OF THE PERCENTAGE OF METAL EXPOSED ON LOW LOADED CERIA SUPPORTED RHODIUM CATALYSTS

摘要

Benzene hydrogenation, a structure insensitive reaction, was used to determine the percentage of metal exposed on low loaded ceria supported rhodium 0.15 to 0.33 wt% Rh/CeO2 catalysts. Catalysts were prepared from nitrated and chlorinated precursors. Freshly prepared catalysts and catalysts aged in air at 1173 K were studied. Hydrogen chemisorption carried out at 313 K on the chlorinated catalysts could be used to confirm the technique since, due to the presence of Cl- ions on the samples, no hydrogen spillover was observed after reduction at 773 K, Data obtained from benzene hydrogenation were found to be in very good agreement with the percentages of metal exposed as calculated from hydrogen chemisorption measurements, Benzene hydrogenation was able to count very low percentages of metal exposed and it was shown from the data obtained for the nonchlorinated catalysts that, unlike hydrogen chemisorption, it was not disturbed by the hydrogen spillover occurring on some Rh/CeO2 systems, The stability of the metal phase was investigated when rhodium was deposited on both high and low surface area ceria, It appeared that anionic exchange on a low specific surface area ceria could lead to a catalyst which, after calcination at 1173 K and reduction at 773 K, exhibits the same amount of exposed metallic rhodium atoms compared to a catalyst prepared from a high specific surface area ceria, hence, containing 50% more rhodium. (C) 1996 Academic Press, Inc. [References: 34]