Abstract
The adsorptive properties of CeO 2 and ZrO 2 were studied with respect to NO and CO 2 probe molecules using temperature-programmed desorption (TPD). Four species were detected during thermal desorption of NO adsorbed on CeO 2 and ZrO 2, namely, NO ( m/ e = 30), N 2 ( m/ e = 28), N 2 O ( m/ e = 44) and O 2 ( m/ e = 32). The TPD profile suggest that there are two types of adsorbed states of NO on the CeO 2 and ZrO 2 surfaces, one is the weakly adsorbed NO which desorbs at about 170°C and the other is the more strongly adsorbed NO which desorbs at about 450°C. The adsorbed NO undergoes extensive decomposition to form N 2, N 2O and O 2 during thermal desorption. The TPD spectrum obtained after CO 2 adsorption on CeO 2 are composed of CO 2 desorption at 140°C and 440°C. These peaks are assigned to monodentate and bidentate carbonate species in the adsorbed states. After the successive adsorption of NO and CO 2 on the CeO 2 and ZrO 2 surfaces, the intensity of CO 2 desorption peak in TPD is weaker than that in the case of single of CO 2. However, the intensity of NO desorption is almost the same as in the case of single NO adsorption. This indicated that the preadsorption of NO on cation sites of oxide surfaces affected the surrounding surface oxygen sites and blocked the CO 2 adsorption. Furthermore, this also indicates that the interaction of the oxide surface with NO is much stronger than that with CO 2.
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