Carbon dioxide reduction on Ir(111): stable hydrocarbon surface species at near-ambient pressure

Stable hydrocarbon surface species in the carbon dioxide hydrogenation reaction on Ir(111) were identified by means of infrared-visible sum-frequency generation vibrational spectroscopy and X-ray photoelectron spectroscopy under near-ambient pressure conditions (0.1 mbar). By introducing gas phase binary and ternary mixtures of CO2, CO, and H-2 into the reaction chamber, stable ethylidyne and ethynyl species were found at the metal surface above 425 K, in remarkable analogy with that observed during the ethylene decomposition process yielding graphene. In addition, upon increasing temperature (up to 600 K depending on the reaction conditions), vibrational and electronic spectroscopic fingerprints appeared that could be attributed to the nucleation of aromatic hydrocarbons at the edge of metastable graphenic clusters interacting with the metal surface.