Table 2. Amount of 18O Exchanged (mmol 18O g–1) at 500 °C over the TM-Doped Ceria along with the Pristine Ceria Solids Following the Step-Gas Switch Ar → 2 vol % 18O2/2 vol % Kr/Ar (15 min)a.
| catalyst | 18O-exchanged (mmol g–1) | CO consumed (mmol g–1) | C16O2 (mmol g–1) | C16O18O (mmol g–1) | C18O2 (mmol g–1) |
|---|---|---|---|---|---|
| Cu–Ce–O | 8.85 (88.5)b | 6.3 (63)d | 0.65 (6.5)b | 1.75 (17.5)b | 2.46 (24.6)b |
| Co–Ce–O | 8.58 (116.0)b | 4.1 (55.4)d | 0.43 (5.8)b | 1.15 (15.5)b | 1.55 (20.9)b |
| Mn–Ce–O | 8.43 (21.6)b | 3.4 (8.7)d | 0.35 (0.90)b | 0.98 (2.5)b | 0.55 (1.4)b |
| Zn–Ce–O | 1.57c | 0.6 | 0.21 | 0.11 | 0.02 |
| CeO2 | 1.48 (16.1)b | 0.28 (3.04)d | 0.05 (0.5)b | 0.07 (0.8)b | 0.02 (0.3)b |
a
Amounts (mmol g–1) of CO consumed and C16O2, C16O18O, and C18O2 formed at 250 °C during the step-gas switch Ar → 4 vol % CO/1 vol % Kr/Ar (20 min) following 16O/18O exchange at 500 °C.
b
Number in parentheses denotes the equivalent number of surface monolayers of lattice oxygen based on the theoretical surface oxygen density for ceria (6.2 μmol m–2). This estimation considers the BET area based on which the equivalent surface monolayer of 16O per gram basis is as follows: Cu–Ce–O = 0.1 mmol g–1, Co–Ce–O = 0.074 mmol g–1, Mn–Ce–O = 0.39 mmol g–1, and CeO2 = 0.09.
c
Equivalent surface monolayers were not estimated, given the nonfluorite structure of the Zn–Ce–O solid material.
d
Equivalent CO in surface coverages of lattice oxygen reacted off.