Structure and reaction properties of thin Al films deposited on Ni(110)

A variety of experimental techniques, including scanning tunneling microscopy (STM) and thermal desorption spectroscopy (TDS) have been used to investigate the structure and reaction properties of thin Al films on Ni(110) as a model for technical Raney nickel catalysts. The measurements show that ill grows by the Volmer-Weber growth mode, with Al islands reaching a height of 30 Angstrom before the first Al layer is completed. On exposure to deuterium the TDS spectra indicate that the addition of Al produces a new deuterium chemisorption state with a desorption energy which decreases from 27 to 14 kJ/mol with increasing deuterium coverage. This new bound stare is attributed to deuterium atoms bound to adsorption sites in the vicinity of Al islands. Thermal desorption measurements also reveal that the deuterium initial sticking coefficient S-o decreases with Al coverage. The results can be explained by a simple model which shows that for low Al coverages each Al island inhibits deuterium dissociation in a region which is about three times larger than the island area. (C) 1998 Published by Elsevier Science B.V. All rights reserved.