Hydrogen
Evolution from Metal–Surface Hydroxyl
Interaction
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Abstract
The redox interaction between hydroxyl
groups on oxide surfaces
and metal atoms and clusters deposited thereon, according to which
metals get oxidized and hydrogen released, is an effective route to
tune both the morphological (particle size and shape) and electronic
(oxidation state) properties of oxide-supported metals. While the
oxidation state of the metals can straightforwardly be probed by X-ray
based methods (e.g., XPS), hydrogen is much more difficult to capture,
in particular in highly reactive systems where the redox interaction
takes place directly during the nucleation of the metals at room temperature.
In the present study, the interaction of Pd with a hydroxylated MgO(001)
surface was studied using a combination of vibrational spectroscopy,
electronic structure studies including Auger parameter analysis, and
thermal desorption experiments. The results provide clear experimental
evidence for the redox nature of the interaction by showing a direct
correlation between metal oxidation and hydrogen evolution at slightly
elevated temperature (390 K). Moreover, a second hydrogen evolution
pathway opens up at 500 K, which involves hydroxyl groups on the MgO
support and carbon monoxide adsorbed on the Pd particles (water–gas
shift reaction)