Adsorption and Oxidative Adsorption of Sulfur Dioxide on γ-Alumina

Abstract

The adsorption and oxidative adsorption of SO_2 on γ-Al_2O_3 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 SO_2 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-Al_2O_3 was contacted with a mixture of SO_2 and O_2, adsorption of SO_2 and oxidation of the adsorbed SO_2 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 (SO_2-O_2-N_2;SO_2-N_2;O_2-N_2;N_2) strongly suggests that surface SO_2 and surface sulfate involve the same active sites such that SO_2 adsorption is inhibited by already formed sulfate. The results also indicate a broad range of site strengths.

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