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 PtAl 3 O 5–7 –, 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 PtAl 3 O 6 –, 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 PtAl 3 O 7 –, the resulting PtAl 3 O 6 – 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 PtAl 3 O 6 – 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.