In-situ X-ray absorption study of ceria-supported Pd-Cu nanoparticles for oxygen-enhanced water gas shift

The detailed structures of bimetallic Pd-Cu on various CeO₂ and Al₂O₃ supports were investigated by X-ray absorption technique in-situ in hydrogen and WGS conditions. No indication of the neighboring Pd atoms in both Pd-K edge and Cu-K edge EXAFS fittings showed that Pd is highly dispersed in the lattice of metallic Cu. The Cu-Cu bond distance was markedly shortened by alloying with Pd and correlated to decrease of coordination number, which reflects particle size. A higher coordination number for Pd-Cu than that for Cu-Cu on Al₂O₃ support suggested that Pd is in the interior of the nanoparticles on Al₂O₃ while these coordination numbers were close on CeO₂ support indicating a uniform distribution of Pd and Cu atoms. The CO shift activity was not simply correlated to the Cu-Cu bond distance or particle size, but the high activity of Pd-Cu/CeO₂ was attributed to surface Pd interacting with Cu on CeO₂ surface.