Reaction of alkanes and cycloalkanes on silica-supported platinum and platinum-gold alloy catalysts

Abstract

The reactions of a range of cyclic and acyclic alkanes in excess hydrogen on silica-supported Pt and 10% Pt 90% Au were examined in a continuous-flow reactor. Catalysts were characterized by X-ray diffraction, electron microscopy, and hydrogen chemisorption measurement. Alloy homogenization required heat treatment at 700 °C following reduction in hydrogen. From a negligible hydrogen chemisorption capacity the alloy catalyst is inferred to have a surface platinum content of <0.4%. In the 300–400 °C temperature range the alloy catalyst was found to have good bond-shift activity and also to be quite active in the ring enlargement of methylcyclopentane to benzene. It was found to be inactive for 1,5- and 1,6-cyclization, the hydrogenolysis of neopentane and of ethane, and also for the ring opening of cyclopentane. Absence of cyclization activity is ascribed to a surface topography of the dilute-Pt alloy unsuited to this demanding reaction on account of the severe heat pretreatment used. Bond-shift activity of such a surface is evidence for a single-site mechanism for this reaction.