THE EFFECTS OF RHENIUM AND SULFUR ON THE REACTIVITY AND SELECTIVITY OF PT SINGLE-CRYSTAL CATALYSTS

Platinum-rhenium bimetallic surfaces have been prepared by condensing Re on Pt(111) crystal surfaces in ultrahigh vacuum (UHV) using a pulsed metal vapor vacuum arc plasma gun. Conversion reactions of n-hexane and cyclohexane have been studied. The same reactions were also performed over sulfided surfaces made by depositing atomic sulfur on the metal in UHV. The presence of Re on Pt(111) greatly increases the hydrogenolysis of n-hexane. Sulfiding of the catalysts suppresses hydrogenolysis and enhances the cyclization activity of n-hexane toward methylcyclopentane. The maximum reactivity for cyclization to form five-membered rings over the sulfided Pt-Re surfaces is obtained when the Pt surface is covered by 1 monolayer (ML) of Re. When the Pt(111) surface is covered by 1 ML of Re, the sulfided catalyst is twice as active as the unsulfided catalyst for cyclization of n-hexane. Presulfiding also enhances the dehydrogenation activity of cyclohexane over the Pt-Re bimetallic surfaces. In that case, maximum reactivity of sulfided catalysts is observed when the Pt surface is covered by 0.5 ML of Re. We conclude that the Pt-Re bimetallic catalyst shows its unique properties when it is combined with sulfur. © 1992.