The effects of Cl-induced alloying in Pt-Sn/Al2O3 catalysts on butane/H-2 reactions

The effects of oxidation/reduction regeneration treatments, with and withou t 1,2-dichloropropane present as a chlorinating agent, on the structure of Pt(3%)-Sn(4.5%)/Al2O3 catalysts have been correlated with selectivities for butane/H-2 reactions. Particles of Pt-0 fin CI-free catalysts were partly covered by Sn-0, but retained exposed ensembles of Pt atoms which were acti ve for isomerisation, hydrogenolysis and dehydrogenation reactions, the lat ter becoming dominant at high reaction temperatures. Coking reduced Pt ense mble size and, hence, also favoured high selectivities for dehydrogenation as hydrogenolysis and isomerisation sites became poisoned. In contrast, the addition of 1,2-dichloropropane in an oxychlorination step before reductio n promoted 1 : 1 Pt-0-Sn-0 alloy formation after reduction, the proportion of the total Pt in alloy being enhanced by increasing 1,2-dichloropropane c oncentration and oxychlorination temperature. The alloy surfaces were inact ive for isomerisation and hydrogenolysis reactions, giving dehydrogenation as the sole catalytic reaction.