Surface composition and structural changes on titanium oxide-supported AuPd nanoparticles during CO oxidation

Abstract

To investigate the influence of morphological changes on the performance of bimetallic catalyst nanoparticles, two AuPd/TiO₂ catalysts with the same starting composition were synthesized via thermal treatments in reducing (H₂) or oxidizing (O₂) atmospheres, resulting in different morphologies. The surface composition of the bimetallic particles evolved under a CO oxidation reaction environment, thereby changing the performance of both catalysts in repeated heat ramps. In the oxidized material, composed mainly of large AuPd particles and PdO particles, the CO oxidation reaction led to a broadening in the size distribution caused by the appearance of smaller particles, together with an increase in the surface Pd concentration. In the reduced material, the CO oxidation reaction led to particle aggregation, Pd oxidation, and surface Pd enrichment in Pd-rich particles. During the CO oxidation experiments, the oxidized material was activated (decrease of T_light-off), while the reduced catalyst suffered a deactivation process (increase of T_light-off). Our results showed that the catalysts converge to a common surface composition and performance, and this convergence seemed to be independent of the initial particle morphology.