Visualizing the Birth and Monitoring the Life of a Bimetallic Methanation Catalyst.

Well-defined bimetallic heterogeneous catalysts are not only difficult to synthesize in a controlled manner, but their elemental distributions are also notoriously challenging to define. Knowledge of these distributions is required for both the as-synthesized catalyst and its activated form under reaction conditions, where various types of reconstruction can occur. Success in this endeavor requires observation of the active catalyst via analytical methods. As a step toward this goal, we present a composite material composed of bimetallic nickel-ruthenium nanoparticles supported on a protonated zeolite (Ni-Ru/HZSM-5) and probe its evolution and function as a photoactive carbon dioxide methanation catalyst using X-ray absorption spectroscopy (XAS). The working Ni-Ru/HZSM-5, as a selective and durable photothermal CO methanation catalyst, comprises a corona of Ru nanoparticles decorating a Ni nanoparticle core. The specific Ni-Ru interactions in the bimetallic particles were confirmed by XAS, which reveals significant electron transfer from Ni to Ru. The light-harvesting Ni nanoparticle core and electron-accepting Ru nanoparticle corona serve as the CO and H dissociation centers, respectively. These Ni and Ru nanoparticles also promote synergistic photothermal and hydrogen atom transfer effects. Collectively, these effects enable an associative CO methanation reaction pathway while hindering coking and fostering high selectivity toward methane.