Catalytic activities of sonochemically prepared Au-core/Pd-shell-structured bimetallic nanoparticles immobilised on TiO₂ and its dependence on Pd-shell thickness

Catalytic activities of sonochemically prepared Au-core/Pd-shell-structured bimetallic nanoparticles (NPs) immobilised on TiO₂ were evaluated. Comparing with the mixture of monometallic Au and Pd NPs on TiO₂, core/shell-immobilised catalysts exhibited higher activities for the partial reduction of nitrobenzene (NB) to aniline (AN), suggesting that the synergistic effect originating from the core/shell structure enhanced the catalytic activities. In the case of high Au/Pd ratios, where the Pd-shell thickness was calculated to be 0.5 nm or lower, infrared spectroscopic measurements of adsorbed CO showed that the Au cores were successfully covered with Pd shells. It was found that a thin Pd shell of one layer or two layers of Pd atoms effectively catalysed the reduction of NB under ambient temperature, whereas the formation of AN was not confirmed on monometallic Au NP-immobilised catalysts.