Co-adsorption of CO and O2 on Fe: II. Calorimetric determination of heats of adsorption on polycrystalline Fe films and thermal desorption spectroscopy

A combination of calorimetric measurement of heat of adsorption and of thermal desorption spectroscopy (TDS) is used to study the adsorption of CO and O 2 as well as co-adsorption of both gases on Fe films. There is a strong influence of the sequence of admission of the gases on their adsorption behaviour. Oxygen is able to block adsorption sites of CO as well as to replace CO from the surface. Generally, TDS is not able to give information on the situation at the adsorption temperature, neither in the case of CO adsorption, nor in the case of co-adsorption of CO and O 2 . The use of labelled oxygen ( 18 O 2 ) improves the value of TDS experiments in such systems.