Characterization of sulfur on Pt-alkali metal/Al2O3 catalysts treated with H2S by a temperature-programmed reaction using deuterium and its role in the dehydrogenation of isobutane

This paper discusses the promotion of isobutane dehydrogenation due to sulfur species adsorbed on Pt-alkali metal (Li, Na, or K)/Al2O3 catalysts. A treatment with hydrogen sulfide at 833 K increased the selectivity to isobutene on all Pt-alkali metal/Al2O3 catalysts. The promotion effect of sulfurization was most significant on a Pt (1 wt%)-Na2O (3 wt%)/Al2O3 catalyst; the selectivity increased from almost 0 for a reduced catalyst to 75% for a sulfurized catalyst. The effect on the selectivity of the addition of alkali metals increased in the order sodium > potassium > lithium. Temperature-programmed reaction (TPR) experiments, conducted by flowing deuterium onto the sulfurized catalysts, were used to characterize the sulfur species that easily desorbed with hydrogen. The results indicated that HS- is the major species on the catalysts and that the adsorbed HS- bridges the PtSir and the Na2Sir particles. Re-reduction of the sulfurized Pt-Na2O/Al2O3 catalyst to remove the HS- decreased the selectivity from 75 to 8%, implying that HS- is effective in enhancing the selectivity.