| AVS 61st International Symposium & Exhibition | |
| Surface Science | Monday Sessions |
| Session SS+AS+EN-MoM |
| Session: | Mechanistic Insights into Surface Reactions: Catalysis, ALD, etc. |
| Presenter: | Miquel Salmeron, Lawrence Berkeley National Laboratory |
| Authors: | B.A.J. Lechner, Lawrence Berkeley National Laboratory Y. Kim, Seoul National University, Korea H. Kang, Seoul National University, Korea M.B. Salmeron, Lawrence Berkeley National Laboratory |
| Correspondent: | Click to Email |
Water (H2O) and ammonia (NH3) are arguably the most important inorganic molecules in the chemical industry. Both have the ability to form hydrogen bonds and mix readily in the liquid form. However, upon adsorption onto a metal surface, the molecules can form fewer yet more directional hydrogen bonds. To investigate the interaction between these two species at the molecular level we present a scanning tunneling microscopy (STM) study of the co-adsorption of water and ammonia on Pt(111), a substrate which bonds both molecules strongly but does not promote their decomposition.
Prior investigations have suggested the formation of the ammonium ion, NH4+, upon adsorption of ammonia onto a water monolayer on Ru(0001) [1], implying that the two molecules react readily when adsorbed on transition metal surfaces. Furthermore, a theoretical study of the co-adsorption of ammonia and water on Cu(110) proposed an intimately mixed layer of ammonia and water as the energetically most favorable structure [2].
Here, we present the first microscopic investigation of co-adsorbed water and ammonia species. Upon adsorption at 4 K, ammonia and water form disordered structures, yet as the temperature is increased the two species segregate on the substrate. Indeed, at temperatures above 77 K, ammonia invariably prefers to bond to the Pt surface and only adsorbs on a water film once the monolayer is complete and no active sites remain on the substrate. When adsorbed on the water layer, we find that ammonia bonds to the water molecules that are lifted off the substrate due to a lattice mismatch of the water monolayer and the Pt(111) geometry, which we believe is due to their ability to provide a hydrogen atom for the hydrogen bond more readily than the molecules bonded more strongly to the substrate.
[1] Y. Kim, E. Moon, S. Shin, H. Kang, Angew. Chem. Int. Ed. 51, 12806 (2012).
[2] G. Jones, S. J. Jenkins, Phys. Chem. Chem. Phys. 15, 4785 (2013).