Abstract
The adsorption of SO2 on Al2O3 and on 3% sodium on Al2O3 preactivated at 350 and 600 degrees C has been studied by gravimetry, thermodesorption, infrared spectroscopy, and Raman spectroscopy. The quantity of SO2 adsorbed is greater on Na/Al2O3. A comparison of the results showed that physical adsorption occurs on weak basic O2- Or OH- sites. Chemisorption mainly arises from adsorption on basic sites through the formation of sulfite species (AlOSO2) which are characterized by an infrared band near 1060 cm-l 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 Na/Al2O3 than on Al2O3, and they were less reactive toward H2S. This is attributed to the greater basicity of the 3% sodium-doped catalyst and accounts for the lower reactivity of Na/Al2O3 relative to pure Al2O3. On either Al2O3 or Na/Al2O3, no sulfur was produced if gaseous SO2 was added to preadsorbed H2S. However, in the reverse sequence, 2H(2)S(g) + SO2(ads) --> (3/n)S-n + 2H(2)O, sulfur was detected via Raman spectroscopy.