L-zeolite-supported platinum and platinum/tin catalysts for isobutane dehydrogenation

Abstract

Catalysts prepared by supporting tin and platinum in the potassium form of L-zeolite exhibit high activity and selectivity for isobutane dehydrogenation and resistance to deactivation at 673–773 K. Mössbauer spectroscopic results show that some of the tin interacts with platinum to form Pt Sn alloy particles in reduced Pt/Sn/K-L catalysts, while the remainder of the tin is present as Sn 2+. Potassium displaced by Sn 2+ from ion-exchange positions in the zeolite may interact with Pt Sn particles in the catalyst. The addition of excess potassium to Pt/Sn/K-L catalysts further enhances the dehydrogenation activity and selectivity. It is suggested that tin and potassium in Pt/Sn/K-L decrease the size of the surface platinum ensembles, thereby inhibiting isomerization and hydrogenolysis reactions of isobutane. The high activity for isobutane dehydrogenation over Pt/Sn/K-L catalysts may be attributed to stabilization of molecularly adsorbed isobutane species by the zeolite pore structure and/or by excess potassium, which enhances the rate limiting dissociation of isobutane.