HYDROGEN CONTROL OF PLATINUM-CATALYZED SKELETAL REACTIONS OF ALKANES: SELECTIVITES AND SURFACE SPECIES

Article abstract of DOI:10.1021/j100411a010

Conversions of n-pentane, n-hexane, 3-methylpentane, n-heptane, 2-methylhexane, 3-methylhexane, 3-ethylpentane, 2,3-dimethylpentane, 2,4-dimethylpentane, 2,2-dimethylpentane, 3,3-dimethylpentane, n-octane, and 2-methylheptane to aromatics, skeletal isomers, C5-cyclic products, and fragments were studied on Pt black catalysts and compared to each other.Yields of these skeletal reactions show maxima as a function of the hydrogen pressure between 5 and 60 kPa (35 and 450 Torr) hydrogen pressure.Low hydrogen pressures favor highly dehydrogenated surface intermediates leading to aromatization and/or hydrogenolysis.Under higher hydrogen pressures, C5-cyclic intermediates prevail: these give cyclopentane and/or skeletal isomers.Radiotracer studies confirm that the main route of skeletal isomerization involves C5-cyclic intermediates.A new type of hydrogenolysis, "C5-unit splitting", is reported.Comparison of the present results with single-crystal data by Somorjai et al. permits us to suggest that the hydrogen control of the selectivites by controlling the surface intermediates may be valid for both types of catalysts.