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Formate synthesis on Cu(100)

We show that copper-formate surface species can be synthesized from CO2(g) + H2(g) on a well defined single Cu(100) crystal. The presence of the surface formate is confirmed and studied by XPS, HREELS and TPD. With the use of a high-pressure cell incorporated into the UHV system, the formate formation was studied over a pressure range 0.5-5.0 bar and a temperature range 313-363 K. The rate of formate formation was found to have a strong dependence on gas composition (CO2:H2) and a weak dependence on total pressure. At 363 K, the initial rate of formate formation on the Cu(100) surface in a 70:30 (CO2:H2) gas mixture at 2.3 bar was found to be approximately 3.3 × 10-4 formate molecules per copper atom per second. The activation energy for the formate formation was found to be 53 kJ mol-1. A gas-solid equilibrium model for the formation of surface formate suggests that the rate-limiting step in the synthesis is the reaction of surface atomic hydrogen with CO2 forming the surface formate.