Atomically precise noble metal clusters (Ag10, Au10, Pd10 and Pt10) on alumina support: A comprehensive DFT study for oxidative catalysis

Abstract

A comprehensive study of electronic and geometrical properties of alumina supported M10 (M = Ag, Au, Pd, Pt) clusters has been reported with a focus to unravel chemical reactivity towards oxidative catalysis. Au10, Ag10 and Pd10 clusters on alumina surface, adopt zigzag style hexagonal pseudo-planar structure aligning to substrate template, contrary Pt10@Al2O3 does not follow surface template and forms a bilayer structure due to higher PtPt bond strength. Pd10 and Pt10 cluster bind with alumina surface stronger than Ag10 and Au10 and accordingly receives more charge from surface. The d-band centre of finite size M10@Al2O3 cluster follows the trends of extended M(111) surface and Pt10@Al2O3 shows close matching for d-band centre position values with Pt(111). On interaction with O2 molecule, all four M10@Al2O3 clusters energetically prefer surface assisted molecular adsorption (O2 bridging cluster-surface) over atop molecular adsorption demonstrating pivotal role of substrate. In contrast, dissociative adsorption prefers atop mode configurations. During oxidation, whilst Ag10@Al2O3, Au10@Al2O3 and Pd10@Al2O3 show increase in MM bond-lengths and move away from substrate, Pt10@Al2O3 displays robust behaviour by moving near to surface. Due to minimum overlap between 4d and 5s state (large difference in energy) the O2 interaction energetics of Ag10@Al2O3 as well as Ag(111) depart from usual d-band model.