Towards Plasmon-Enhanced Heterogeneous Catalysis on Metal Nanoparticles

Abstract

Heterogeneous catalysis is a vital part of the chemical industry. The energy efficiency is, for many processes, somewhat less than desired. The main reason for this is high operating temperatures due to activation barriers. Research has shown that catalysts which also are plasmonically active yield higher reaction rates under illumination. It is theorised that hot electrons originating from the decay of plasmonic resonances assist in molecular dissociation via transient electron attachment. In reactions where dissociation is associated with the rate-limiting step, this could enhance the reaction rate at constant temperature. Plasmonic structures are characterised by build-ups in electric field intensity in the vicinity of the structure, as well as elevated absorption efficiencies (Qabs > 1). Due to the low energy efficiencies of catalytic reactions, it is of interest to utilise plasmonic nanostructures to aquire new reaction pathways. A structure with a Au plasmonic nanoantenna, above which Pt catalytic particles are deposited, is proposed. The electric field surrounding the Au nanoantenna would induce a polarisation in the catalytic particle, and hence, enhance the energetic charge carrier creation via locally enhanced absorption. The proposed structure is created using hole-mask colloidal lithography together with physical evaporation techniques. An experimental assembly is designed to test the structures. A significant increase in catalytic rate is observed under illumination of the sample, however, the effect is not conclusively determined to be connected to the plasmonic nanoantennas since it is also observed during illumination of only the catalyst itself. This implies a direct optical excitation in the catalyst nanoparticle as the reason for the observed enhancement.