JO URNA L O F MO LEC ULA R C A TA LYSIS ELSEVIER Journal of Molecular Catalysis 93 ( 1994) 67-78 High temperature treated Pt / Sn-ZnAl,O, catalysts P. Boscha,*, M.A. Valenzuelaavb, B. Zapatab, D. Acostac, G. Aguilar-Riosb, C. Maldonadob, I. Schifterb zyxwvutsrqponmlkjihgfe “Departamento de Quimica, Universidad Autdnoma Metropolitana (Iztapalapa), A.P. H-534, M&co D.F., 09340, Mexico bInstituto Mexican0 de1 Petrbleo, A.P. 14-805, Mhico D.F., 07730, Mexico ‘Institute de Fisica, CJNAM, A.P. 20-364, M&co D.F., 01000, Mexico Received 27 December 1993; revised 3 May 1994; accepted 11 May 1994 zyxwvutsrqponmlkjihgfedcb Abstract Sn-ZnAl,O, mixed supports were prepared by coprecipitation method with Sn contents of 0.5, 1.6 and 3 wt.%. Later Pt ( 1 wt.%) was incorporated by impregnation and samples reduced in hydrogen at 823 and 1073 K. Chemisorption data showed a decrease in hydrogen as temperature increases which is attributed to Pt-Sn alloy formation. Catalytic activity in isobutane dehydrogenation and n- heptane dehydrocyclization seems to be dependent on the amount of metallic Pt phase. Pt/Sn-ZnAl,O, catalysts were thermally more stable than Pt/ZnA1204 preparation. Tin alters the ZnAl,O, properties towards a higher thermal stability, but if added in more than 1 wt.%, it alloys with platinum inhibiting catalytic performance. Keywords: Aluminate; Dehydrogenation; High temperature treatment; Platinum; Tin; Zinc 1. Introduction Naphtha reforming as well as paraffin dehydrogenation reactions are catalyzed by platinum-tin on alumina catalysts. Although active and selective, these catalysts sinter and deactivate easily. New supports inhibiting particle growth, hence, have to be studied and ceramics seem to be an adequate option. It has been shown, indeed, that Pt/Al,O, is more prone to metal sintering than Pt/MgAl,O, [ 11. Like Pakhomov et al. [ 21, we have chosen ZnA&O, to support platinum-tin, and studied some features of Pt/ZnAlzOd interactions. We have found, in previous works [3,4] that preparation methods alter the resulting catalyst structure and, therefore, the catalytic properties. However, it has been difficult to establish a clear *Corresponding author. 0304-5102/94/$07.00 0 1994 Elsevier Science B.V. All rights reserved .SSDlO304-5 102( 94)00095-D