Synergy Effect of Two Sets of Sing-Atom Sites (Ni1 and Ru1) on CeO2 for Reforming CH4

Heterogeneous catalysis is performed on specific sites on surface of a catalyst even if the specific sites of many catalysts could not be readily identified. Here we report a catalyst consisting of two sets of single-atom sites on surface of CeO₂ nanorods. It is highly active with turn-over rate of producing 73.6 H₂ molecules on each site per second through reforming CH₄ with CO₂ and highly selective (98.5% selectivity) for producing H₂ at a relatively low temperature down to 500^oC. The anchored Ni and Ru atoms on CeO₂ surface are singly dispersed and remained at cationic state during catalysis at 500^oC. The two types of single-atom sites, Ni₁ and Ru₁ play synergy role in this catalysis, evidenced by lower apparent activation barrier and higher turn-over rate for production of H₂ and CO in contrast to a catalyst with Ni₁ single-atom sites (Ni_0.05Ce_0.95O₂) and one with Ru₁ single-atom sites (Ni_0.05Ce_0.95O₂). Computational studies uncovered the molecular mechanism of the synergy effect which is originated at the differently preferred roles of Ni₁ and Ru₁ in activations of CH₄ and CO₂, respectively and at the sequential roles in first formation of atomic hydrogen from CH₄ on Ni site and then coupling H atoms to form molecular H₂ on Ru₁ site. This demonstration of synergy effect of two sets of single-atom sites on the same surface suggests a new avenue for designing a catalyst with high activity and selectivity at a relatively low temperature.