CHEMISORPTION AND TPD STUDIES OF HYDROGEN ON NI AL2O3/

The activities of two supported nickel catalysts, a commercial (17 wt. -% Ni/Al2O3) and a non-commercial (10 wt.-% Ni/Al2O3) catalyst, were i nvestigated in gas phase toluene hydrogenation. Both catalysts were ac tive in hydrogenation, exhibiting rate maxima at about 443 K. The cata lysts were characterized using hydrogen chemisorption and temperature programmed desorption (TPD) techniques. Decreasing hydrogen adsorption capacity was generally found in the temperature interval 298-423 K, t he capacity of both the commercial and the non-commercial Ni-catalysts being about 20 cm(3)/g(Ni) at 423 K. No effect on the total adsorptio n capacity was found by increasing the pretreatment temperature from 5 03 K to 773 K on the commercial catalyst. Three adsorption states of h ydrogen (I-III) were resolved from the TPD-spectra of both catalysts, Hydrogen desorption was modelled with peak shape analysis as a second order process with free readsorption, giving hydrogen adsorption entha lpies ranging from -108 to -124 kJ mol(-1) for adsorption state I. The kinetic data and the TPD studies indicate that the decrease of the to luene hydrogenation activity at temperatures above 443 K is due to the decay of adsorption state I.