  Transition metal carbides have sparked unprecedented enthusiasm as
high-performance catalysts in recent years. Still, the catalytic properties of
copper (Cu) carbide remain unexplored. By introducing subsurface carbon (C) to
Cu(111), displacement reaction of proton in carboxyl acid group with single Cu
atom is demonstrated at the atomic scale and room temperature. Its occurrence
is attributed to the C-doping induced local charge of surface Cu atoms (up to
+0.30 e/atom), which accelerates the rate of on-surface deprotonation via
reduction of the corresponding energy barrier, thus enabling the instant
displacement of a proton with a Cu atom when the molecules land on the surface.
Such well-defined and robust Cu$^{\delta +}$ surface based on the subsurface C
doping offers a novel catalytic platform for on-surface synthesis.
