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The adsorption of SO2 on A1203 and on 3% sodium on A1203 preactivated at 350 and 600 "C has been studied by gravimetry, thermodesorption, infrared spectroscopy, and Raman spectroscopy. The quantity of SOz adsorbed is greater on NdA1203. A comparison of the results showed that physical adsorption occurs on weak basic 0,or OH-sites. Chemisorption mainly arises from adsorption on basic sites through the formation of sulfite species (AlOS02) which are characterized by an infrared band near 1060 cm-'. Other minor species such as disulfite or hydrogen sulfite were postulated in order to account for (1) a perturbation of surface OH groups and (2) the constant quantity of chemisorbed species which form as a function of the temperature of activation. The sulfite species were more stable on NdAlzO3 than on Al2O3, and they were less reactive toward HzS. This is attributed to the greater basicity of the 3% sodium-doped catalyst and accounts for the lower reactivity of NdAl2O3 relative to pure A1203. On either A1203 or NdAlzO3, no sulfur was produced if gaseous SO2 was added to preadsorbed H2S. However, in the reverse sequence, 2HzS(g) + S02(ads) -(3/n)S, + 2H20, sulfur was detected via Raman spectroscopy.

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