Overlayer Stacking Promotes Hydrogen Spillover

Hydrogen spillover (HSO) has attracted significant attention due to its important role in elucidating the synergistic interactions between separated active sites during catalysis; however, it is controversial since the driving force of hydrogen migration is unclear. Herein, atomic layer deposition (ALD) was employed to spatially separate well-defined Pd/Ni nanoparticles (NPs), enabling the clear identification of HSO at mild reaction conditions (i.e., 343 K) during alkyne semihydrogenation over aNi/nMO_<i>x</i>/Pd@support catalysts, in which Pd is unreachable. Interestingly, ALD stacking of the Ti-, Zr-, Zn-, or Al-oxide overlayers significantly enhanced the HSO, attributed to the "chimney effect", and the driving force of hydrogen migration was attributed to the concentration difference between Pd-NPs and Ni-NPs during catalysis.