Applied Surface Science, Vol.161, No.3-4, 406-416, 2000
SO2 adsorption and thermal stability and reducibility of sulfates 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 SOx emission 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 N-2 adsorption-desorption and infrared spectroscopy (IR) measurements. The behavior of SO2 adsorption and oxidation on the surface of catalyst was evaluated with IR from 50 degrees C to 600 degrees C. Particularly, the thermal stability and H-2-reducibility of the formed sulfite or sulfate during SO2 adsorption 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 550 degrees C in vacuum. The bulk-like sulfate, however, showed a high ability to resist H-2-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.
Keywords:magnesium-aluminate spinel;sulfur-transfer catalyst;SO2 emissions;oxidative adsorption;reducibility;thermal stability;FCC unit