Fine-Tuning of Pt Dispersion on Al2O3 and Understanding the Nature of Active Pt Sites for Efficient CO and NH3 Oxidation Reactions

Fine-tuning the dispersion of active metal species on widely used supports is a research hotspot in the catalysis community, which is vital for achieving a balance between the atomic utilization efficiency and the intrinsic activity of active sites. In this work, using bayerite Al(OH)₃ as support directly or after precalcination at 200 or 550 °C, Pt/Al₂O₃ catalysts with distinct Pt dispersions from single atoms to clusters (ca. 2 nm) were prepared and evaluated for CO and NH₃ removal. Richer surface hydroxyl groups on AlO_x(OH)_y support were proved to better facilitate the dispersion of Pt. However, Pt/Al₂O₃ with relatively lower Pt dispersion could exhibit better activity in CO/NH₃ oxidation reactions. Further reaction mechanism study revealed that the Pt sites on Pt/Al₂O₃ with lower Pt dispersion could be activated to Pt⁰ species much easier under the CO oxidation condition, on which a higher CO adsorption capacity and more efficient O₂ activation were achieved simultaneously. Compared to Pt single atoms, PtO_x clusters could also better activate NH₃ into -NH₂ and -HNO species. The higher CO adsorption capacity and the more efficient NH₃/O₂ activation ability on Pt/Al₂O₃ with relatively lower Pt dispersion well explained its higher CO/NH₃ oxidation activity. This study emphasizes the importance of avoiding a singular pursuit of single-atom catalyst synthesis and instead focusing on achieving the most effective Pt species on Al₂O₃ support for targeted reactions. This approach avoids unnecessary limitations and enables a more practical and efficient strategy for Pt catalyst fabrication in emission control applications.