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)3as support directly or after precalcination at 200 or 550 °C, Pt/Al2O3catalysts with distinct Pt dispersions from single atoms to clusters (ca. 2 nm) were prepared and evaluated for CO and NH3removal. Richer surface hydroxyl groups on AlOx(OH)ysupport were proved to better facilitate the dispersion of Pt. However, Pt/Al2O3with relatively lower Pt dispersion could exhibit better activity in CO/NH3oxidation reactions. Further reaction mechanism study revealed that the Pt sites on Pt/Al2O3with lower Pt dispersion could be activated to Pt0species much easier under the CO oxidation condition, on which a higher CO adsorption capacity and more efficient O2activation were achieved simultaneously. Compared to Pt single atoms, PtOxclusters could also better activate NH3into –NH2and –HNO species. The higher CO adsorption capacity and the more efficient NH3/O2activation ability on Pt/Al2O3with relatively lower Pt dispersion well explained its higher CO/NH3oxidation 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 Al2O3support for targeted reactions. This approach avoids unnecessary limitations and enables a more practical and efficient strategy for Pt catalyst fabrication in emission control applications.