(177a) Highly Active and Stable Pt1/CeOx/SiO2 Single-Atom Catalyst for CO Oxidation

The lack of stability associated with sintering of isolated metal (M₁) atoms poses significant limitations of single-atom catalysts (SACs) for practical applications. Strong anchoring of M₁ to supports may alleviate sintering but often at the cost of activity. Under oxidative environment, metal atoms can be stabilized by oxygen ligands. Such anchored metal atoms, however, become unlink and sinter under reducing environment, especially at high temperatures. We recently developed a new platform of functional nanoglues which not only confine isolated metal atoms to prevent sintering but also enhance the activity of the targeted catalytic reaction. Such a design strategy allows evaluation of the intrinsic activity of CO oxidation over calcined and reductively activated Pt₁/CeO_x/SiO₂ SACs. Treatment of an as-prepared Pt₁/CeO_x/SiO₂ SAC at 600°C in 5% oxygen made this catalyst inactive for low temperature CO oxidation. After reductive activation of a calcined Pt₁/CeO_x/SiO₂ SAC, the T₉₀ (the temperature for 90% CO conversion), however, reduced from 285°C to 80°C, leading to a specific rate of 0.93 mol_CO·mol_Pt^-1·s^-1, at 80 °C, the highest among all CeO₂-supported Pt catalysts. Under oxygen-rich CO oxidation conditions, CeO₂-supported Pt atoms/clusters are, however, oxidized, significantly reducing their capability for CO oxidation. Properly activated Pt₁/CeO_x/SiO₂ SACs demonstrated excellent resistance to oxidative deactivation. After O₂ treatment at 400°C for 3 hours, the T₉₀ was still 99 °C and this catalyst was stable after 5cycles of CO oxidation with ramp temperatures up to 300 °C. The abundance of Ce³⁺ in ultra-small (< 2 nm), isolated CeO_x nanoglue islands is responsible for strong localization of Pt atoms to prevent sintering and for oxidative resistance during CO oxidation.