KINETICS OF ALKANE HYDROGENOLYSIS ON CLEAN AND COKED PLATINUM AND PLATINUM-RHENIUM CATALYSTS

The dependences of rate upon H-2 and alkane pressures have been determined for the hydrogenolysis of ethane, propane and n-butane on clean and coked Pt/Al2O3 and Pt-Re/Al2O3 catalysts. On clean surfaces, preserved by using only 1 min reaction periods, rates usually exhibited maxima as H-2 pressure was increased, the pressure at the maximum increasing with the size of the alkane; orders in the alkane measured at high H-2 pressure approximated to unity. Coking by reacting n-butane + H-2 at 713 K caused significant differences in the ways in which rates varied with H-2 pressure. Three rate equations have been tested, of which two give satisfactory fits. Constants for one of these, viz. rate = k1P(A)P(H)/(k2P(A) + P(H)k3) are presented, from which it appears that the reactive species may be formed from the reactant alkane by loss of four or five H atoms.