The Light Stuff: Enabling Sustainable, Product-Selective Photocatalysts with Plasmonics
Chemical manufacturing is critical for industries spanning construction, clothing, plastics, pharmaceuticals, food, and fertilizers, yet remains among the most polluting and energy-demanding practices. Our vision is to enable sustainable chemical production with atomically-architected photocatalysts that precisely control molecular interactions for high-efficiency and product-selective chemistry. Controlling photochemical transformations requires bridging the length-scale between a catalyst’s atomic-scale structural features that influence dynamics and the macroscale extrinsic parameters that can be controlled (e.g., illumination, temperature, pressure). Optical excitation of plasmons offers a solution for overcoming this size mismatch - creating nanoscopic regions of high electromagnetic field intensity that can modify electronic and molecular energy levels, enable access to excited-state dynamics, and open new reaction pathways that are impossible to achieve under typical conditions. Further, plasmons can be efficiently excited with sunlight or solar-driven LEDs, for sustainable chemical transformations.
Here, we present our research advancing plasmon photocatalysis from the atomic to the reactor scale. First, we describe advances in in-situ atomic-scale catalyst characterization, using environmental optically-coupled transmission electron microscopy (OTEM). With both light and reactive gases introduced into the column of an electron microscope, we can monitor chemical transformations under various illumination conditions, gaseous environments, and at controlled temperatures, correlating three-dimensional atomic-scale catalyst structure with photo-chemical reactivity. Then, we describe how these atomic-scale insights enable optimized reactor-scale performance. As model systems, we consider two reactions: 1) acetylene hydrogenation with Ag-Pd catalysts and 2) CO2 reduction with Au-Pd catalysts. Here, Au/Ag acts as a strong plasmonic light absorber while Pd serves as the catalyst. We find that plasmons modify the rate of distinct reaction steps differently, increasing the overall rate more than ten-fold. Secondly, reaction nucleation occurs at electromagnetic hot-spots – even when those hot-spots do not occur in the preferred nucleation site. Finally, plasmons open new reaction pathways that are not observed without illumination, enabling both high-efficiency and selective catalysis with tuned bimetallic composition. Our results help elucidate the combined roles of optical, electronic and chemical contributions to plasmon photocatalysis, en-route to record efficiency and selectivity.