Effects of Support on Sulfur Tolerance and Regeneration of Pt Catalysts Measured by Ethylene Hydrogenation and EXAFS

The effect of support on sulfur tolerance and regenerability under reducing environments was investigated by rate measurements for ethylene hydrogenation, hydrogen chemisorption, and extended X-ray absorption fine structure (EXAFS). Catalysts, 1 % Pt/Al2O3 and 1 % Pt/P25 (TiO2), were tested after sulfidation in H2S/H-2 at 250 A degrees C followed by regeneration treatments in H-2 at 250, 350 and 450 A degrees C. Our combined results showed a 20-27 times decrease in the rate of ethylene hydrogenation on both sulfided catalysts, accompanied by a 4-6 times drop in the Pt surface area. Regenerations up to 450 A degrees C were unable to remove all the sulfur, as evidenced by the presence of Pt-S bonds by EXAFS at about 2.25-2.33 , characteristic lengths for chemisorbed sulfur and bulk-type PtS. However, a partial recovery of the hydrogenation rate per mole of Pt was observed on sulfided Pt/Al2O3 after reduction at 450 A degrees C, while the induction of strong metal support interactions (SMSI) at reduction temperature above 350 A degrees C was observed on Pt/P25, regardless of the presence of sulfur. For Pt/P25, the reversal of the SMSI state together with sulfur removal by mild oxidation suggests that sequential reduction/oxidation treatments may be more effective in restoring the S-free state of TiO2-supported catalysts. Pt/Al2O3 and Pt/TiO2 (P25) sulfur tolerance and regenerability were evaluated after reduction treatments in H-2. Both catalysts were equally poisoned by sulfur based on C2H4 hydrogenation. Reduction treatments up to 450 A degrees C were not able to remove sulfur on either catalyst. Sulfur on Pt may inhibit the formation of the SMSI state on Pt/TiO2, especially below 350 A degrees C.