Mechanisms of Oxidase and Superoxide Dismutation-like Activities of Gold, Silver, Platinum, and Palladium, and Their Alloys: A General Way to the Activation of Molecular Oxygen

Metal
and alloy nanomaterials have intriguing oxidase- and superoxide
dismutation-like (SOD-like) activities. However, origins of these
activities remain to be studied. Using density functional theory (DFT)
calculations, we investigate mechanisms of oxidase- and SOD-like properties
for metals Au, Ag, Pd and Pt and alloys Au4–xMx (x = 1, 2,
3; M = Ag, Pd, Pt). We find that the simple reactiondissociation
of O2supported on metal surfaces can profoundly
account for the oxidase-like activities of the metals. The activation
(Eact) and reaction energies (Er) calculated by DFT can be used to effectively
predict the activity. As verification, the calculated activity orders
for series of metal and alloy nanomaterials are in excellent agreement
with those obtained by experiments. Briefly, the activity is critically
dependent on two factors, metal compositions and exposed facets. On
the basis of these results, an energy-based model is proposed to account
for the activation of molecular oxygen. As for SOD-like activities,
the mechanisms mainly consist of protonation of O2•– and adsorption and rearrangement of HO2• on metal surfaces. Our results provide
atomistic-level insights into the oxidase- and SOD-like activities
of metals and pave a way to the rational design of mimetic enzymes
based on metal nanomaterials. Especially, the O2 dissociative
adsorption mechanism will serve as a general way to the activation
of molecular oxygen by nanosurfaces and help understand the catalytic
role of nanomaterials as pro-oxidants and antioxidants.