Mf. Luo et al., CHARACTERIZATION STUDY OF CEO2 SUPPORTED PD CATALYST FOR LOW-TEMPERATURE CARBON-MONOXIDE OXIDATION, Catalysis letters, 50(3-4), 1998, pp. 205-209
Catalysts consisting of palladium supported on cerium dioxide (Pd/CeO2
) were prepared and used for carbon monoxide oxidation in a stoichiome
tric mixture of carbon monoxide and oxygen. Pd/CeO2 exhibits high cata
lytic activity for the oxidation of CO, showing markedly enhanced cata
lytic activities due to the combined effect of palladium and cerium di
oxide. The Pd/CeO2 catalyst is superior to Pd/ZrO2, Pd/Al2O3, Pd/TiO2,
Pd/ZSM-5 and Pd/SiO2 catalysts with regard to the activity under the
conditions examined. The catalysts were characterized by means of XRD
and TPR. The position of the H-2-TPR peak shifts to lower temperature
with increasing Pd loading from 0.25 to 2.0%. CeO2 inhibits the hydrog
en reduction of PdO. CO-TPR measurements have shown the existence of t
hree peaks. The low-temperature peak (alpha) is due to the Pd hydroxid
e species. The beta peak has been attributed to finely dispersed PdO.
The high-temperature peak (gamma) has been attributed to crystal phase
PdO. Crystal phase PdO is more difficult to reduce by CO than finely
dispersed PdO. On the basis of the catalytic activity and CO-TPR resul
ts, we conclude alpha species (Pd hydroxide) mainly contribute to the
catalytic activity for low-temperature CO oxidation.