Disentangling the size-dependent geometric and electronic effects of palladium nanocatalysts beyond selectivity.

The prominent size effect of metal nanoparticles shapes decisively nanocatalysis, but entanglement of the corresponding geometric and electronic effects prevents exploiting their distinct functionalities. In this work, we demonstrate that in palladium (Pd)-catalyzed aerobic oxidation of benzyl alcohol, the geometric and electronic effects interplay and compete so intensively that both activity and selectivity showed in volcano trends on the Pd particle size unprecedentedly. By developing a strategy of site-selective blocking via atomic layer deposition along with first principles calculations, we disentangle these two effects and unveil that the geometric effect dominates the right side of the volcano with larger-size Pd particles, whereas the electronic effect directs the left of the volcano with smaller-size Pd particles substantially. Selective blocking of the low-coordination sites prevents formation of the undesired by-product beyond the volcano relationship, achieving a remarkable benzaldehyde selectivity and activity at the same time for 4-nm Pd. Disentangling the geometric and electronic effects of metal nanoparticles opens a new dimension for rational design of catalysts.