SO₂ adsorption on alumina and sulfation with SO₂ + O₂ have been investigated by IR spectroscopy and thermogravimetric measurements at temperatures quite similar to Claus process plant operating conditions (280-350°C). The sulfation was studied under various P(SO₂) and P(O₂) pressures. The results allow a kinetic model for alumina sulfation to be proposed. The elementary steps of the mechanism involve two types of surface site. The same site contributes to SO₂ adsorption as sulfite and to sulfate formation. Another catalytic site leads to oxygen dissociation. On pure alumina the number of this last site is very low. The model enables the weight gain due to the fixation of SO₂ and O₂ to be expressed as a function of time. Kinetic constants were calculated from various sulfation experiments and the theoretical expression so obtained fits the experimental curves.