The Influence of the Metal-support Interaction on the Catalytic Activity of Pt/Al2O3 and Pt/TiO2 in NH3 Oxidation.

In the current work the activity of Pt/Al₂O₃ and Pt/TiO₂ catalysts in the reaction of NH₃ oxidation was studied depending on the calcination temperature. A combination of XRD, TEM, XPS and TPR methods was applied in order to analyze the influence of the interaction between active component and support on the catalytic properties of the samples. Catalysts were prepared by incipient wetness impregnation using the Pt(NO₃)₄ solution with calcination at 400, 600 and 800°C. A highly dispersed Pt⁰ particles with the average particles size ~1 nm were observed after calcination at 400°C for both Pt/Al₂O₃ and Pt/TiO₂ samples. However, Pt/TiO₂ catalyst showed better catalytic characteristics at the lowtemperature range with the temperature of 50% NH₃ conversion (T₅₀) about 175°C. The calcination of the Pt/Al₂O₃ catalyst at T>400°C improved the low-temperature activity due to the formation of large Pt⁰ particles. The T₅₀ value did not vary significantly for Pt/TiO₂ samples calcined at different temperatures. Based on XPS, XRD and TPR-H₂ data the strong metal-support interaction (SMSI) was shown for Pt/TiO₂ catalysts. SMSI resulted in the stabilization of platinum in a highly dispersed state even after high temperature calcination. Pt/Al₂O₃ sample calcined at 800°C had the highest specific catalytic rate of NH₃ oxidation. The high activity of the catalyst is likely due to the presence of Pt⁰ particles with optimal size distribution. [ABSTRACT FROM AUTHOR]