Coverage-dependent dissociation of H2O on Pd/MgO(100)/Mo(100)

The adsorption of H2O on Pd deposited upon MgO(100) thin films prepared on Mo(100) was studied using low-energy electron diffraction, ultraviolet photoelectron spectroscopy and high-resolution electron energy loss spectroscopy. A non-metallic feature of Pd has been observed at the coverage of Pd less than 1.5 monolayer equivalents (MLE) on the MgO(100) films. Partially dissociated H2O was detected on Pd/MgO(100)/Mo(100), and H2O dissociates most readily at similar to 0.5 MLE Pd coverage. This coverage-dependent dissociation has arisen from a combination of the size effect of Pd particles and a vacancy-induced modification of surface reactivity.