Catalytic CO Oxidation on Single Pt-Atom Doped Aluminum Oxide Clusters: Electronegativity-Ladder Effect

Abstract

Single platinum-atom catalysts exhibit extraordinary activity in a large number of reactions. However, a consensus regarding the molecular origin of Pt catalysis is far from being reached. Here, benefiting from the study of atomic clusters, we propose the Electronegativity-Ladder (E-Ladder) effect to account for the origin of Pt catalysis. The concept was obtained from the study of single Pt-atom doped aluminum oxide clusters PtAl3O5-7-, which are catalytically active in CO oxidation by molecular O-2. The undoped aluminum oxide clusters, however, cannot drive such a catalytic cycle. The reactions have been identified by mass spectrometry and density functional theory calculations. The key to drive the cycle lies in the unique structure of PtAl3O6-, in which the Pt atom that is not fully oxidized can coexist with the highly oxidative oxygen-centered radical (O-center dot). After the oxidation of one CO by PtAl3O7-, the resulting PtAl3O6- can also oxidize a second CO. The E-Ladder effect originates from the well-fitting electronegativity of the Pt atom (2.28) in between that of the Al atom (1.61) and the O atom (3.44), and this effect promotes the generation of an unpaired electron localized O-center dot radical, which results in the oxidative nature of PtAl3O6- toward CO. Thus, the large enthalpy in the catalytic reaction (2CO+ O-2 -> 2CO(2)) can be distributed much more evenly into several elementary reactions in the Pt-Al-O system than in the pure Al-O system.