SO adsorption and thermal stability and reducibility of sulfates 2 formed on the magnesium–aluminate spinel sulfur-transfer catalyst

Magnesium–aluminate spinel used as a sulfur-transfer catalyst in the fluid catalytic cracking units for SO emission x control was prepared by the precipitation method. The crystalline structure, textural property, and surface dehydroxylation of the sample were characterized by thermogravimetry–derivative thermogravimetry TG–DTG., differential thermal analysis DTA., X-ray diffraction XRD., liquid N2 adsorption–desorption and infrared spectroscopy IR.measurements. The behavior of SO2 adsorption and oxidation on the surface of catalyst was evaluated with IR from 508C to 6008C. Particularly, the thermal stability and H2-reducibility of the formed sulfite or sulfate during SO2adsorption or oxidation were tested under various conditions. In the absence of oxygen in the feed mixture, weak physically adsorbed SO2 species and surface sulfite were identified. In the case of SO2 oxidative adsorption, both surface sulfate and bulk-like sulfate were formed. When the sulfated sample was reduced with hydrogen, the surface sulfite and sulfates were completely removed below 5508C in vacuum. The bulk-like sulfate, however, showed a high ability to resist H2-reduction, which indicates that the reducibility of bulk-like sulfate formed on magnesium–aluminate spinel must be enhanced when it is used as a sulfur-transfer catalyst. q2000 Elsevier Science B.V. All rights reserved.