Temperature programmed desorption of co from reduced perovskite oxides LnCoO 3−x (Ln=La, Sm)

Abstract

The adsorption of CO on LnCoO 3−x (Ln=La, Sm) was studied by temperature programmed desorption (TPD) method. At least two different sites were indicated by two CO TPD peak in both cases. The peak temperatures were 803 K(I) and > 933 K(II) for LaCoO 3−x (x=0.77), 823 K(I) and > 923 K(II) for SmCoO 3−x (x=0.51), respectively. The activation energies of desorption for CO(I) were 58 kJmol −1 for LaCoO 3−x and 74 kJmol −1 for SmCoO 3−x. These values were close to the dissociation energy between Co and bridged CO of Co 2(CO) 8. On the contrary, the desorption of CO 2 was observed, together with the desorption of CO, after the adsorption of CO on the reduced samples. The desorption of CO 2 was affected by the adsorbed partial pressure of CO and the adsorbed temperature. Thus, it is considered that the formation of CO 2 is due to the disproportionation reaction of adsorbed CO on LnCoO 3−x; 2CO → C + CO 2. The formation of CO 2 was further discussed by the XPS experiments.