Synergy of Single-Atom Ni₁ and Ru₁ Sites on CeO₂ for Dry Reforming of CH₄

Abstract

Heterogeneous catalysis performs on specific sites of a catalyst surface even if specific sites of many catalysts during catalysis could not be identified readily. Design of a catalyst by managing catalytic sites on an atomic scale is significant for tuning catalytic performance and offering high activity and selectivity at a relatively low temperature. Here, we report a synergy effect of two sets of single-atom sites (Ni₁ and Ru₁) anchored on the surface of a CeO₂ nanorod, Ce_0.95Ni_0.025Ru_0.025O₂. The surface of this catalyst, Ce_0.95Ni_0.025Ru_0.025O₂, consists of two sets of single-atom sites which are highly active for reforming CH₄ using CO₂ with a turnover rate of producing 73.6 H₂ molecules on each site per second at 560 °C. Selectivity for producing H₂ at this temperature is 98.5%. The single-atom sites Ni₁ and Ru₁ anchored on the CeO₂ surface of Ce_0.95Ni_0.025Ru_0.025O₂ remain singly dispersed and in a cationic state during catalysis up to 600 °C. The two sets of single-atom sites play a synergistic role, evidenced by lower apparent activation barrier and higher turnover rate for production of H₂ and CO on Ce_0.95Ni_0.025Ru_0.025O₂ in contrast to Ce_0.95Ni_0.05O₂ with only Ni₁ single-atom sites and Ce_0.95Ru_0.05O₂ with only Ru₁ single-atom sites. Computational studies suggest a molecular mechanism for the observed synergy effects, which originate at (1) the different roles of Ni₁ and Ru₁ sites in terms of activations of CH₄ to form CO on a Ni₁ site and dissociation of CO₂ to CO on a Ru₁ site, respectively and (2) the sequential role in terms of first forming H atoms through activation of CH₄ on a Ni₁ site and then coupling of H atoms to form H₂ on a Ru₁ site. These synergistic effects of the two sets of single-atom sites on the same surface demonstrated a new method for designing a catalyst with high activity and selectivity at a relatively low temperature.