C O M M U N I C A T I O N S
Results of CO-TPR confirm the oxidation of CO to CO2, even
at room temperature, and the participation of four different surface
oxygen species with different operating conditions (Supporting
Information). The high-temperature oxygen species (548 °C) are
associated with lattice oxygen, which do not participate in the
catalytic oxidation of CO at low temperatures.15 The oxygen species
with a maximum uptake at 113 and 201 °C may be attributed to
surface oxygen species (superoxide and peroxide adspecies, re-
spectively), in agreement with Raman results.15 Furthermore, cyclic
TPR experiments (Supporting Information) demonstrate the regen-
eration of the gold active sites during reduction and oxidation of
the catalyst.
In summary, the data demonstrate that both cationic and metallic
gold are present in the gold catalyst prepared with nanocrystalline
CeO2, and that the catalytic active sites incorporate cationic gold.
Nanocrystalline CeO2 stabilizes O2 as superoxide and peroxide
species, whereas the precipitated CeO2 tends to stabilize O2δ- and
molecular O2. Furthermore, nanocrystalline CeO2 supplies reactive
oxygen in the form of surface η1 superoxide species and peroxide
adspecies at the one-electron defect site to the supported active
species of gold for the oxidation of CO.
Figure 1. Correlation between Au3+ and Au0 species and specific rate for
CO oxidation catalyzed by gold supported on nanocrystalline CeO2. Infrared
band frequency and intensity of CO adsorption on gold catalysts were used
to identify Au3+ (band at 2148 cm-1 representing Au3+-CO) and Au0 (band
at 2104 cm-1 representing Au0-CO).
Acknowledgment. This research was supported by the Spanish
CICYT (MAT 2003-07945-C02-01) and the Auricat EU network
(HPRN-CT-2002-00174).
Supporting Information Available: Experimental details and
additional results. This material is available free of charge via the
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