Supported Metal Catalysts; Preparation, Characterisation, and Function: Part VI. Hydrogenolysis of Ethane, Propane, n-Butane and iso-Butane over Supported Platinum Catalysts

Abstract

The catalytic properties of three supported platinum catalysts, 0.75 wt% Pt/SiO2, 0.89 wt% Pt/Al2O3, and 0.48 wt% Pt/MoO3, are reported for the hydrogenolysis of ethane, propane, n-butane, and iso-butane. The reactions were carried out in a flow reactor at atmospheric pressure. The apparent activation energies, Eapp, for the hydrogenolysis reactions and the isomerisation reactions of n-butane and iso-butane, all show a compensation effect with the corresponding values of ln Aapp. This compensation effect can be accounted for by the dehydrogenative chemisorption of the alkanes as the first step in the reaction mechanisms to both hydrogenolysis and isomerisation. No apparent structure sensitivity was demonstrated by the three catalysts for the hydrogenolysis of ethane. The Pt/Al2O3catalyst showed the highest activity of the three catalysts for the hydrogenolysis of propane. This high activity can be related to the strong adsorption of alkane fragments on platinum sites on the Pt/Al2O3catalyst which exhibit δ+ polarisation. Over the Pt/SiO2and Pt/Al2O3catalysts the isomerisation of n-butane and iso-butane can be explained by a metal-only catalysed isomerisation route. Very high levels of isomerisation over the Pt/MoO3catalyst agree with a bifunctional mechanism involving acid sites on the MoO3support.