One-step conversion of n-butane to isobutene over H-beta supported Pt and Pt,M (M = Cu, In, Sn) catalysts: An investigation on the role of the second metal

The one-step transformation of n-butane to isobutene was studied over H-beta zeolite supported Pt and Pt,M (M = Cu, In, Sn) catalysts. Catalytic performance of monometallic Pt/H-beta samples resulted to be affected by the support acidity, a lower number of acid sites leading to higher iso-and n-butenes selectivities and lower by-products formation. Addition of Cu, In or Sn to Pt enhanced both isobutene and n-butenes selectivities, which were in the order: Pt,In > Pt,Sn >> Pt,Cu > Pt. All Pt,M samples exhibited also a higher stability than the corresponding monometallic Pt samples, the sequence of deactivation rates being: Pt > In,Pt > Cu,Pt approximate to Sn,Pt. On the basis of characterization results it was stated that the addition of Cu, In or Sri to Pt affects the n-butane dehydroisomerization modifying both the surface structure of Pt clusters and the support acidity. In particular the observed order of isobutene selectivity was related to the degree of Pt-M interaction leading to a dilution of Pt clusters, which inhibits hydrogenolysis reactions and enhances dehydrogenation processes. The decrease in the number of acid sites caused by addition of the second metal was instead accounted for the improved resistance to deactivation of Pt,M catalysts. (c) 2006 Elsevier B.V. All rights reserved.