From Ammonia Synthesis to Methane Conversion: Enabling Sustainable Chemical Manufacturing with Atomically-Optimized Photocatalysts

Chemical manufacturing is critical for industries spanning construction, plastics, pharmaceuticals, food, and fertilizers, yet remains among the most energy-demanding practices. Optical excitation of plasmons offers a route to more sustainable chemical synthesis. Plasmons create 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. In particular, we explore how bimetallic nanoparticles interact with hydrogen and nitrogen (separately and together), in order to probe reduction reactions including 1) nitrogen fixation with AuRu catalysts; 2) acetylene hydrogenation with Ag-Pd catalysts; 3) CO2 reduction with Au-Pd catalysts; and 4) methane coupling with AuRu nanoparticles. With light, temperature, 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. Additionally, using atomic-electron tomography and 4D scanning transmission electron microscopy, we can correlate the three-dimensional atomic-scale catalyst structure with photo-chemical reactivity. Next, we describe how these TEM-based atomic-scale insights enable optimized reactor-scale photocatalytic performance. In all cases, Au/Ag acts as a strong plasmonic light absorber while Pd/Ru serves as the catalyst. We find that plasmons modify the rate of distinct reaction steps differently and that reaction nucleation occurs at electromagnetic hot-spots – even when those hot-spots do not occur in the preferred nucleation site. Plasmons also open new reaction pathways that are not observed without illumination, enabling both high-efficiency and selective catalysis with tuned bimetallic catalyst composition. Our results provide a roadmap for how atomically-architected photocatalysts can precisely control molecular interactions for high-efficiency and product-selective chemistry.