Adsorbed and Subsurface Absorbed Hydrogen Atoms on Bare and MgO(100)-Supported Pd and Pt Nanoparticles

Heterogeneous catalysts customarily contain active metal nanoparticles (NPs) deposited on oxides. It is often difficult to understand in detail the influence of supports on NP properties based solely on experimental data. Here, we study by means of electronic structure calculations the effect of a rather chemically inert defect-free support MgO(100) on adsorption and absorption properties of 1.6 nm large Pd-127 and Pt-127, NPs representative of bigger species. We show that metal nanostructuring only slightly affects adsorption of single hydrogen atoms on terrace sites. At the same time, structural flexibility of the NPs increases thermodynamic stability of subsurface H in Pt NPs and seems to kinetically assist absorption of H in both Pd and Pt. For H bound to Pd, NPs influence of the support is only noticeable near the metal oxide interface, while for Pt NPs H atoms more distant from the interface are also affected. Overall, the support is found to change the binding energies of H to Pd-127 and Pt-127 NPs by less than 0.1 eV. Quantitative estimates of the differences between adsorption and absorption properties of bare and MgO-supported noble metal NPs are important for modeling of catalytic systems not featuring strong metal-support interactions.