Towards the promoting roles of SO2 in total oxidation of propane over Pt catalysts

Abstract

The effect of SO₂ on the total oxidation of propane over supported Pt catalysts (e.g., Pt/AlF₃, Pt/γ-Al₂O₃, Pt/SiO₂) was investigated in this work. The catalytic testing results revealed that the addition of 100 ppm SO₂ in the reaction feed could significantly improve the activity. The largest improvement was obtained on the Pt/AlF₃ catalyst, on which a 10-fold higher reaction rate (1.15 μmol g⁻¹ s⁻¹ at 220 °C) was achieved in the presence of SO₂ compared to that in the absence of SO₂ (0.12 μmol g⁻¹ s⁻¹ at 220 °C). Detailed characterizations such as Fourier transform infrared spectroscopy (FTIR), NH₃ temperature-programmed desorption, and X-ray photoelectron spectra results revealed that the presence of SO₂ in the reaction feed resulted in the formation of sulfates on the catalyst surface, which enhanced the surface acidity and lowered surface charge density of Pt species. The in-situ FTIR results of propane oxidation revealed an enhanced C–C bond cleavage of propane molecules by the addition of SO₂. The kinetic investigation further clarified the origin of such enhancement, that is, the addition of SO₂ slightly strengthened propane adsorption while greatly weakened the oxygen adsorption on the Pt species, and such synergy facilitated the kinetically-relevant surface reaction (i.e., C–C cleavage). Therefore, the findings establish a general agreement on the promoting roles of SO₂ on the reaction. Moreover, the current work emphasizes the influence of surface sulfate on the adsorption/activation of oxygen, which has been rarely recognized in previous works.