Temperature-programmed desorption study of carbon monoxide adsorbed on magnesium oxide

Abstract

The nature of the different types of CO adsorbed on MgO has been studied by the temperature-programmed desorption technique. Three desorption peaks for CO appeared in the temperature-programmed desorption profile at ca. 430 K (peak I), 470 K (peak II) and 560 K (peak III). The relative amounts of these three types of adsorbed CO varied with the pretreatment temperature of MgO and with the adsorption conditions. Peaks I, II and III reached a maximum when the MgO sample was pretreated at 873, 773 and 1273 K, respectively. The activation energies for the desorption of CO corresponding to peaks I and III were 25.5 and 42.2 kJ mol^–1, respectively.

Peak-I CO reacted more easily with O₂ than peak-III CO. The former reacted at 273 K while some of the latter remained unreacted at 423 K. On the basis of ¹³CO tracer experiments it is suggested that the conversion of peak-I CO to peak-III CO is irreversible, and that the adsorption sites are common for both peak-I CO and peak-III CO.