Reactions of Surface and Subsurface hydrogen (both atomic & molecular) over Pd-Zinc Oxide single crystal surfaces in UHV condition.

Sub-surface or bulk hydrogen has attracted considerable attention due to its unique reactivity for several important heterogeneous chemical reactions on the catalyst surface. Compared to surface hydrogen, sub-surface hydrogen atoms approach to adsorbed species from different directions and new reaction channels can be operative. In addition to that, Hydrogen atoms evolve from the bulk with high energy and readily hydrogenate surface adsorbed species. Gas phase hydrogen atoms have been utilized to produce both surface and bulk hydrogen to investigate the reactions of surface and sub-surface Hydrogen on a ZnO single crystal surface. A Pd/ ZnO surface has been produced to put H atoms on ZnO using molecular hydrogen and dissociation of molecular hydrogen over Pd surface was observed. Moreover, desorption took place around 450K for surface hydrogen and around 550K for bulk hydrogen. Interaction of hydrogen with the ZnO surface has been investigated using various surface science techniques including temperature desorption programmed desorption (TPD), Low energy electron diffraction (LEED), Auger electron spectroscopy (AES).