Ambient-Pressure X-ray Photoelectron Spectroscopy Study of Cobalt Foil Model Catalyst under CO, H₂, and Their Mixtures

Ambient-pressure X-ray photoelectron spectroscopy (XPS) was used to investigate the reactions of CO, H₂, and their mixtures on Co foils. We found that CO adsorbs molecularly on the clean Co surface and desorbs intact in vacuum with increasing rate until ∼90°C where all CO desorbs in seconds. In equilibrium with 100 mTorr gas, CO dissociates above 120°C, leaving carbide species on the surface but no oxides, because CO efficiently reduces the oxides at temperatures ∼100°C lower than H₂. Water as impurities or produced by reaction of CO and H₂ efficiently oxidizes Co even at room temperature. Under 97:3 CO/H₂ mixture and with increasing temperatures, the Co surface becomes more oxidized and covered by hydroxyl groups until ∼150°C where surface starts to get reduced, accompanied by carbide accumulation indicative of CO dissociation. A similar trend was observed for 9:1 and 1:1 mixtures, but surface reduction begins at higher temperatures. (Figure Presented).