Ni-noble metal bimetallic catalysts for improved low temperature CO₂ methanation

Bimetallic nickel-noble metal catalysts with a low noble metal loading (1 wt% of Ru, Pt, Rh, Pd, or Ir) supported on Pr-doped CeO₂ were comparatively evaluated regarding their CO₂ methanation catalytic performance. Ru was the sole noble metal phase that could dramatically promote the catalytic activity of the corresponding monometallic catalyst, whereas the incorporation of the other noble metals either retained (Pt and Ir) or worsened (Rh and Pd) the catalytic performance. The best–performing RuNi bimetallic catalyst maintained around 80 % CO₂ conversion and 99.5 % CH₄ selectivity at 325 °C during 50 h of operation. Ru was found to be well dispersed along the support (as single atoms or small clusters), while a small part of it was also dispersed atop the medium-sized Ni nanoparticles. Its promoting ability was attributed to the improved metal dispersion, catalyst reducibility, moderate basicity and provision of additional active sites for CO₂ and H₂ dissociation, while DFT analysis evidenced that a Ru single atom atop a Ni cluster/ small particle is the structure that is most favorable towards the initial CO₂ adsorption and dissociation.