Hydrogenolysis of propane and of n-butane on Pt/KL zeolite

The reaction of n-butane with H-2 proceeds on a Pt/KL zeolite catalyst between 530 and 640 K, and, with a tenfold excess of H-2, the isomerization selectivity at 623 K lies between 0.40 and 0.75, depending on the form of pretreatment and prior use. In thermal cycling experiments, methane is initially the major product, but with the most active samples the propane selectivity is afterwards greater than that of methane; this strange behaviour may be a consequence of conducting the reaction in a microporous support. Isomerization selectivity increases with temperature. Propane is much less reactive than n-butane. The dependence of the rates of reaction of both these alkanes upon H-2 pressure is modelled by a rate expression derived from a mechanism in which the alkane is chemisorbed and activated by the loss of several H atoms. Rates are strongly inhibited by increasing the H-2 pressure, and values of K-H, the adsorption coefficient for H-2, obtained from the modelling are much higher than for other Pt catalysts. This may to some extent account for the activity of Pt/KL for aromatization of linear alkanes, by suppressing alkene formation and. hence, carbon deposition. (C) 1997 Academic Press.