Heats of Adsorption and Reaction of CO on Iron/Manganese Oxide Catalysts

The heats of adsorption and reaction of CO have been measured on reduced Fe/Mn oxide catalysts of different compositions at temperatures between 263 and 543 K. The heats of adsorption depend only to a small extent on the manganese content of the catalyst and are independent of the temperature of reduction. The former fact points to a more structural than electronic effect of the manganese oxide addition. The heats of adsorption are, however, strongly dependent on measurement temperature, increasing from about 60 kJ mol-1 at 263 K to about 200 kJ mol-1 at 493 K and then decreasing again to about 180 kJ mol-1 at 543 K. This temperature dependence can be explained by consecutive reactions following CO adsorption, i.e. the Boudouard reaction, dissociation of CO and diffusion of carbon into the bulk of iron. The amount of CO adsorbed is correlated to the metallic iron content in the surfaces of the catalysts.