Understanding the strong metal-support interaction of Pd/MgO/Mg interfaces under hydrogen pressure and temperature for hydrogen sensing

Magnesium (Mg) thin films coated with ultrathin palladium (Pd) layers (0.5-5 nm) have been shown to enhance Mg hydrogenation compared to thicker films due to a not yet well-understood strong metal-support interaction. Ex-situ photoelectron spectroscopy and STEM-EDS analysis suggest that the improved kinetic response can be attributed to a dual intermixed Mg-Pd layer: (i) a surface layer composed of Pd covered by MgO/Mg(OH)2 and (ii) a second intermixed region of Pd and metallic Mg below the surface. The role of MgO, which has been extensively characterized both before and after the hydrogenation process, and which, in previous studies, was reported to block hydrogenation in the absence of Pd, remains unclear. This proposal aims to perform an operando characterization of the catalytically active MgO/Pd surface region under realistic conditions to unravel the structural and compositional changes that occur during the hydrogenation process. For this purpose, NAP-XPS will be performed on a set of ex situ Pd/Mg thin films with varying Pd thicknesses and on an uncapped Mg thin film at moderate temperatures (25 ºC – 80 ºC) and H2 pressures (10-5 – 20 mbar). Understanding how the system evolves during the hydrogenation reaction under different conditions is an indispensable step in understanding the MgO/Pd/Mg structure-activity relationship and the electronic interaction established between its constituents.