Préparation et caractérisation des catalyseurs Rh/Al2O3 et Rh/ZnO–Al2O3

A series of rhodium (1 and 5 wt%) deposited on alumina and alumina modified by Zn was prepared by impregnation of Al₂O₃ and ZnO–Al₂O₃ with two different precursors, Rh(NO₃)₂·xH₂O and RhCl₃, followed by calcination at 723 K, and characterized after reduction at different temperatures, in the range 500–800 °C. Catalysts were analysed by Hydrogen Chemisorption (Hc), Temperature-Programmed Reduction (TPR), Temperature-Programmed Desorption (TPD), X-ray diffraction (RDX), and Scanning Electron Microscopy methods. The results show that the metal dispersion depends strongly on the Zn/Rh atomic ratio and on the metal loading. The presence of Zn and high reduction temperature decrease the capacity to chemisorb hydrogen, whereas the metal particles' size increase is probably due to the sintering effect. Temperature-programmed studies (TPR) of catalysts show that the temperature of maximal reduction is lower with nitrate-prepared catalysts, which is explained by metal–support interactions.