w The behavior of formate adsorbed on Cu(110) surface exposed to hydrogen gas was investigated at 300-330 K. Although an exchange reaction from D-COO(a) to H-COO(a) was observed after exposing a DCOO(a)-covered Ni(110) surface to H-2 in a previous report, this did not occur with Cu(110). The preadsorbed DCOO(a) desorbed as DCOOH after accepting a hydrogen atom from a gaseous H-2 molecule.