Methane activation by heteronuclear diatomic AuRh+ cation: comparison with homonuclear Au2+ and Rh2+

Abstract

The ability to activate methane differs appreciably for different transition metals, and it is attractive to find the most suitable metal for the direct conversion of methane to value-added chemicals. Herein, we performed a comparative study on the reactions of CH₄ with Au₂⁺, AuRh⁺ and Rh₂⁺ cations by mass-spectrometry based experiments and DFT-based theoretical analysis. Different reactivity has been found for these cations: Au₂⁺ has the lowest reactivity, and it can activate methane but only produce H–Au₂–CH₃⁺ without H₂ release; Rh₂⁺ has the highest reactivity, and it can produce both carbene-type Rh₂–CH₂⁺ and carbyne-type H–Rh₂–CH⁺ with H₂ release; AuRh⁺ also has high reactivity to produce only AuRh–CH₂⁺ with H₂, avoiding the excessive dehydrogenation of CH₄. Our theoretical results demonstrate that Rh is responsible for the high reactivity, while Au leads to selectivity, which may be caused by the unique intrinsic bonding properties of the metals.