WATER-GAS SHIFT REACTION ON A COBALT MOLYBDENUM OXIDE CATALYST

The activity of a commercial Co-Mo oxide catalyst in the water-gas shi ft reaction was studied with transient response experiments in a gradi entless spinning basket reactor operating at 350-400-degrees-C and at atmospheric pressure. The Co-Mo oxide catalyzed the shift reaction at temperatures above 350-degrees-C, whereas the activity was low at 350- degrees-C. The transient response experiments showed that hydrogen was always formed faster from the surface than carbon dioxide. This princ ipal effect was observed in transients obtained after different cataly st pretreatments with N2, with N2 and H2O as well as with N2, H2O and H-2. Pretreatment with H2O enhanced the transient responses of both H- 2 and CO,. Separate chemisorption studies of H-2, CO, and CO2 indicate d that CO2 is a more abundant surface species than CO and H-2. Based o n the transient response experiments and the chemisorption studies a r eaction mechanism was proposed, which involves water adsorption and de composition steps, a reaction step between CO and surface hydroxyls gi ving H-2 and adsorbed CO2, and finally, a CO2 desorption step. The sur face reaction and CO2 desorption steps were assumed to be rate determi ning. The stationary kinetics were described with a rate equation base d on the rate determining steps, and the behaviour of the transient re sponses was explained with the proposed surface reaction mechanism.