CO oxidation on ceria-based nanocatalysts: Cooperative and non-cooperative behavior for a structure-sensitive reaction

Ceria-based catalysts (namely, CeO2, CePrOx and CePrZrOx) have been prepared to investigate the structuredependency for the CO oxidation. Then, it has been proved that the CO oxidation over ceria nanocatalysts depends on the presence of highly reactive (100) and (110)-type planes. The best performance has been achieved for the Ce-NC catalyst because of the higher amount of low-index surfaces on the CeO2-nanocubes. For catalysts prepared by the Solution Combustion Synthesis (SCS), higher CO conversion values have been reached with ternary and binary oxides rather than with pure ceria, and the following activity order can be drawn: Ce-SCS < CePr-SCS < CePrZr-SCS. Therefore, the presence of Zr and Pr species into the ceria framework improves the catalytic performance, showing a cooperative behavior among the Ce/Pr/Zr/O sites. On the other hand, the oxidation activity with the nanocubic structures increases as follows: CePrZr-NC < CePr-NC < Ce- NC. This means that the presence of Pr/Zr species into the ceria lattice does not have a beneficial effect on the activity (non-cooperative behavior). These findings further confirm that the surface properties of solid catalysts depend on both the electronic and geometric factors. Moreover, CO oxidation is highly sensitive to the electronic and geometric structures of ceria-based catalysts and it appears as a “ill-conditioned system,” since small variations in the catalyst properties give rise to large effects on the activity.