Heat Treatment Improves the Activity and Water Tolerance of Pt/Al2O3 Catalysts in Ammonia Catalytic Oxidation

Ammonia selective catalytic oxidation (NH3-SCO) is a commercial technology applied to diesel vehicles to eliminate ammonia leakage. In this study, a series of Pt/Al2O3 catalysts were synthesized by an impregnation method, and the state of Pt species was carefully adjusted by heat treatment. These Pt/Al2O3 catalysts were further systematically characterized by Brunauer–Emmett–Teller, X-ray diffraction, X-ray photoelectron spectroscopy, X-ray absorption fine structure, UV–vis, H2-tempertaure-programmed reduction, and NH3-temperature-programmed desorption. The characterization results showed that dispersed oxidized Pt species were present on conventional Pt/Al2O3 samples, while high-temperature treatment induced the aggregation of platinum species to form metallic Pt nanoparticles. The Pt/Al2O3 catalysts treated at high temperatures showed superior activity and water tolerance in the NH3-SCO reaction. Diffuse reflectance infrared Fourier-transform spectroscopy combined with mass spectrometry experiments revealed that the Lewis acid sites were more reactive than the Brønsted acid sites. Moreover, compared to oxidized Pt species, metallic Pt nanoparticles were beneficial for oxygen activation and were less affected by water vapor, thus contributing to the superior activity and water tolerance of Pt/Al-800.