Interaction of carbon monoxide with (110) nickel surfaces

Abstract

The interaction of CO with a (110) nickel surface has been investigated using a number of techniques. Auger electron spectroscopy was used to follow the chemical composition of the surface. Using LEED, two ordered chemisorbed CO structures were found to form on the clean surface at room temperature. A (2 × 1) structure is stable at pressures above ${\text{5 × 10}}^{\text{−8}}\mathrm{torr}$ . This structure is replaced by a one‐dimensionally incoherent structure at lower pressures. The isosteric heat of adosorption, determined from LEED structure stability and from Kelvin‐method work function measurements, was approximately 25 kcal/mole for both of the ordered structures. These structures occur for CO coverages greater than 0.7 monolayer. For coverages below 0.7 the isosteric heat rose to approximately 30 kcal/mole. Work function changes greater than +1.3 eV accompany the reversible CO adsorption. Mass‐spectrometric studies of CO desorption indicated that the adsorbed CO can be removed by heating to 450°K. The mean heat of desorption calculated from CO‐desorption spectra was $\text{25.4± 1.1}\mathrm{kcal/mole}$ . Surface decomposition of CO was caused by heating the sample in CO and also by the interaction of impinging electrons with chemisorbed CO. Interaction with CO caused the reduction of an oxygen‐covered surface for sample temperatures above 500°K. An increase in carbon dioxide was detected in the gas phase during this interaction. Electron energy‐loss spectroscopy provided additional information on the interaction of CO with the surface.