The interaction of carbon monoxide with nickel—iron alloys. A comparison between single crystal surfaces and supported catalysts

The interaction of carbon monoxide with nickel—iron alloys is studied on Ni(111)-Fe surfaces by means of ellipsometry and Auger electron spectroscopy, and by means of infrared spectroscopy on γ-Al₂O₃-supported Ni_xFe catalysts. The nickel-to-iron ratio of the alloy strongly affects the interaction with CO. On alloys with an iron atom fraction of 0.3 or less the adsorption of CO is molecular, whereas at fractions higher than 0.4 it is initially dissociative. Surfaces contaminated with carbon and oxygen exhibit a lower heat of adsorption. The presence of pre-adsorbed hydrogen lowers the amount of CO which can be adsorbed on Ni(111)-Fe surfaces, whereas on supported catalysts it leads to the formation of formate species already at room temperature.