Making light work: designing plasmonic structures for the selective photothermal methanation of carbon dioxide†

Effectively engaging light to induce catalytic activity requires the careful selection of a catalyst support with appropriate and beneficial properties. On this basis, black, plasmonic TiN was employed as a Ni catalyst support for the CO₂ methanation reaction under illuminated-only conditions. The positive effects of light illumination were found to be defined by the Ni deposit size and the Ni–TiN interaction. At a high Ni loading (40 wt%, 70 wt%), simulated sunlight induces plasmonic heating through the TiN support which is sufficient to initially in situ reduce the Ni deposits and initiate CO₂ methanation. Photothermal effects from TiN and the metallic Ni, combined with reaction exothermicity, then continue to further reduce the Ni and amplify the methanation reaction. At a lower Ni loading (10 wt%), the Ni deposits are smaller and more dispersed. In this case, the topmost Ni deposit surfaces are more strongly influenced by the TiN support due to their closer proximity to the metal–support interface. DFT calculations revealed that this condition can facilitate the migration of light induced plasmonic hot charge carriers from the TiN towards the exposed Ni surface, altering the surface charge of the Ni. The adsorption strength of *CO is subsequently enhanced to enable further reaction rather than desorption as product, thereby boosting CH₄ selectivity. The findings discern between the different phenomena (plasmonic heating and hot electron migration) invoked by plasmonic excitation and offer new insight on the contribution these phenomena make to governing catalyst activity and selectivity.