The interactions of Na, NO, and H2O on the graphite (0001) surface

Artikel i vetenskaplig tidskrift, 2003

The reactions of Na and NO on the (0001) surface of graphite and the influence of coadsorbed water on these reactions have been studied by thermal desorption spectroscopy. The products of the NO+Na reactions are dependent on the partial concentrations in the initial coadsorbed layer. For NO:Na dose ratios less than 1:1, N2 formation is dominant. For higher NO doses, this is superseded by N2O formation. In all cases sodium is oxidized by the NO. This leads to carbonate formation, which subsequently decomposes to release CO2 and CO. The addition of H2O at low coverages to the Na+NO system complicates the reactions. It results in ammonia formation by two independent mechanisms. The formation of NH3 is strongly dependent on the water dose. In addition to generating NH3, coadsorbed water alters the sodium oxidation pathway resulting in an enhanced formation of CO2 at certain coverages. Large H2O coverages block the NO reaction pathways by forming an inert "hypermetalated" hydroxide overlayer. The surface composition of this hydroxide is of the type Na2OH or Na3OH. Decomposition of this overlayer results in the desorption of a significant fraction of stable Na2OH molecules.