TEMPERATURE-PROGRAMMED DESORPTION (TPD), REACTION (TPR) AND OXIDATION (TPO) OF SPECIES FORMED ON RH/MGO AFTER INTERACTION WITH H2 AND CO

Chemisorption and reaction of CO on a 2.5 wt.% Rh/MgO catalyst appears to be sensitive to the adsorption temperature and the extent of CO/He treatment. CO, CO2 and H-2 are produced during temperature-programmed desorption following CO chemisorption. Results from (CO)-C-13 experiments suggest that most CO2 arises from interaction of CO residing on Rh with -OH groups on the magnesia support, and also from direct interaction of CO with the support. Inactive carbon accumulates on the Rh surface during CO/He treatment at 573 K. This can only partly be removed by H-2 or O2 treatments at 723 K, and is considered to be partly responsible for deactivation of the catalyst and suppression of H-2 and CO chemisorption after prolonged treatment of the catalyst with CO/He. Hydrogen chemisorption on the present Rh/MgO catalyst is found to be an activated process. The results suggest that this activated chemisorbed H-2 is present on the Rh and not on the support.