Nanoporosity-Enhanced Catalysis on Subwavelength Au Nanoparticles: a Plasmon-Enhanced Spectroscopic Study

Using surface-enhanced Raman spectroscopy (SERS) to monitor catalytic reactions in real time on Au nanocatalysts has been a significant challenge because plasmon-enhanced spectroscopies require the utilization of subwavelength Au nanostructures as substrates while heterogeneous catalysis requires small Au nanoparticles in the sub-5 nm size regime. Here, we show that subwavelength Au nanoparticles with nanoscale surface porosity represent a unique bifunctional nanostructure that serves as both high-performance SERS substrates and efficient surface catalysts, allowing one to unravel the kinetics and pathways of surface-catalyzed reactions with unprecedented sensitivity and detail through time-resolved plasmon-enhanced spectroscopic measurements. The origin of the nanoporosity-enhanced catalytic activity can be interpreted as a consequence of high abundance of undercoordinated surface atoms at the steps and kinks on the highly curved surfaces of Au porous nanoparticles. By measuring SERS signals from the monolayer molecules preadsorbed on the surfaces of Au porous nanoparticles, we have been able to gain quantitative new insights into the intrinsic kinetics and mechanisms of Au-catalyzed hydrogenation of aromatic nitro compounds with minimal complication introduced by the molecular diffusion, adsorption, and desorption.