Plasmon-Assisted Indirect Light Absorption Engineering in Small Transition Metal Catalyst Nanoparticles

Light absorption in plasmonic nanoantennas constitutes an interesting way of enhancing catalytic reactions occurring at surfaces of metals nanoparticles by forming hot electron-hole pairs. These can either directly transfer to empty orbitals of adsorbed species on the nanoparticle surface or thermalize via electron-phonon coupling and enhance reaction rates via a photothermal reaction channel. While this scheme, in principle, can be efficient for the well-known plasmonic materials Ag and Au due to their large optical cross-sections, other transition metals, which exhibit excellent catalytic properties, have spectrally broad and weak plasmon resonances. Thus, lower plasmon-induced electron-hole pair excitation is expected, especially for sub-10 nm nanoparticles, typical in heterogeneous catalysis. Here, a solution is presented to circumvent these limitations by challenging the established picture that plasmonic nanoparticles also constitute catalytically active entities in a plasmon mediated hot electron catalysis concept. Light absorption in catalyst nanoparticles can be engineered via an adjacent noble metal plasmonic nanoantenna that efficiently collects incident radiation with low losses, and couples it into the catalytic particles where the energy is dissipated due to the intrinsically high optical losses in transition metals at near-visible frequencies. Absorption enhancement of 1-2 orders of magnitude is predicted in 3-4 nm sized Pd catalyst nanoparticles.