The adsorption and oxidative adsorption of SO2 on γ-Al2O3 have been investigated at temperatures of 500-700°C by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). At temperatures above 500°C the adsorbed SO2 species was characterized by an IR band at 1065 cm-1. The equilibrium coverage and initial rate of adsorption decreased with temperature, suggesting a two-step adsorption. When γ-Al2O3 was contacted with a mixture of SO2 and O2, adsorption of SO2 and oxidation of the adsorbed SO2 to a surface sulfate characterized by broad IR bands at 1070 cm-1 and 1390 cm-1 took place. Sulfate formation was found to be reversible, but the reverse reaction took several hours even at 700°C. The results of a series of TGA experiments under different atmospheres (SO2O2N2;SO2N2;O2N2;N2) strongly suggests that surface SO2 and surface sulfate involve the same active sites such that SO2 adsorption is inhibited by already formed sulfate. The results also indicate a broad range of site strengths.
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