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

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 PtAl₃O_5-7^-, which are catalytically active in CO oxidation by molecular O₂. 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^-•). 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^-• radical, which results in the oxidative nature of PtAl₃O₆^- toward CO. Thus, the large enthalpy in the catalytic reaction (2CO + O₂ → 2CO₂) can be distributed much more evenly into several elementary reactions in the Pt-Al-O system than in the pure Al-O system.