(558ab) Ru Atoms Immobilized on Porous Hexagonal Boron Nitride for CO2 Methanation

Restricting metal atoms on supporting materials is typically carried out via intrinsic ligands coordinating with the support (e.g. oxygen or heteroatom doped supports), or micropore-confined structures by physical restriction (e.g. metal organic frameworks). The defect engineering of hexagonal boronnitride (h-BN) shows high specific surface area and contains B and N vacancies, which are considered to be good intrinsic ligands. Furthermore, h-BN materials possess excellent heat conduction and thermal conductivity (390 Wm^-1K^-1) at room temperature, significantly higher than other traditional oxide supports such as: TiO₂ (8.5 Wm^-1K^-1), SiO₂ (1.4 Wm^-1K^-1), Al₂O₃ (28-35Wm^-1K^-1), and ZnO (50 Wm^-1K^-1). Therefore, h-BN is a promising support for thermalcatalysis, where the unique properties of h-BN will be explored for the immobilization of single metal atoms or clusters to be used in CO₂ hydrogenation.

In this study, by engineering porous h-BN via the introduction of defects we were able to highly disperse ruthenium utilizing a simple filtration method, promoting a strong interaction between the B/N defect sites and ruthenium, and probed their catalytic activity via the surface sensitive CO₂ hydrogenation. The B and N coordination served to reduce the valence state of Ru, which promoted the CO₂ reaction rate and CH₄ selectivity. The structure of the catalyst was verified via XPS, STEM, Raman spectroscopy, and XAFS. Furthermore, by adjusting the loading of the Ru we were able to synthesize atomic Ru at the lowest loading and small Ru clusters as the loading increased. Finally, the catalysts synthesized via the filtration method were bench-marked against Ru/BN catalyst prepared via wet impregnation, where the catalyst prepared via filtration possessed a factor of five greater CO₂ reaction rate, with a corresponding increase in the selectivity towards methane over the Ru/BN prepared via wet impregnation.