Support-Free Bimodal Distribution of Plasmonically Active Ag/AgO_x Nanoparticle Catalysts: Attributes and Plasmon Enhanced Surface Chemistry

A self-regenerative metal/metal oxide nanostructure comprised of a bimodal distribution (e.g., 6 and 160 nm average diameters) of silver (Ag) nanoparticles (NPs) with a AgO_x surrounding is introduced as a new type of plasmonic catalyst through a physical method used in this work. The support-free catalyst shows plentiful surface adsorbed oxygen species along with excellent localized surface plasmon resonance (LSPR) and appreciable photoluminescence (PL). These properties plus the structural features enable highly active catalysis toward reactions of H₂, O₂, CO, and hydrocarbons at ambient to elevated operating temperatures without any deactivation observed over ∼150 h thermal cycles (at 350 °C) of catalytic reaction tests. Over this highly active catalyst, plasmon induced preferential growth of surface oxygen species and surface reactions are demonstrated via in situ Raman spectroscopy. These studies suggest that the enhanced surface species growth and catalytic process result from surface transfer of hot electrons generated by interband transitions with plasmon enhanced local field and intraband transitions with plasmon nonradiative decay. The revealed coupling of energetic plasmons with surface species formation and reactivity can be used to guide rational design of catalysts and processes. The combination of high activity and durability of this plasmonic catalyst makes it viable for potential energy and cost-effective catalytic applications.