Abstract:

The catalytic behavior of metal nanocatalysts is intrinsically contingent on the diversity of their exposed surfaces, which can be substantially regulated through the phase engineering of metal nanoparticles. In this study, it is demonstrated that the face-centered cubic (fcc) phase Ru with a close-packed (111) surface presents superior catalytic activity towards CO₂ methanation. This behavior is attributed to its enhanced capability toward CO₂ chemisorption derived from its inherently high surface reactivity. Complete exposure of such surfaces was successfully achieved experimentally by the synthesis of icosahedral Ru metal nanoparticles, which exhibited remarkable performance for CO₂ methanation with 5-8 times higher activity than its conventional hexagonal close-packed (hcp) counterpart when supported on inert supports. However, for the joined fcc-Ru nanoparticles in the fresh catalyst, an fcc- to hcp-phase transformation was observed at a relatively high temperature with the in situ characterizations, which resulted in metal agglomeration and led to catalyst deactivation. However, the CO₂ conversion was still much higher than that of the hcp-phase Ru nanocatalysts, as the monodispersed particles could maintain their fcc phase. Our results demonstrate that phase engineering of Ru nanocatalysts is an effective strategy for a catalyst design with improved catalytic performance. However, the phase transformation could represent a latent instability of the catalysts, which should be considered for the further development of robust catalysts.

Key words: Phase engineering, Face-centered cubic, Ru nanocatalyst, CO₂ methanation, Phase transformation