Effect of the support in Pt and PtSn catalysts used for selective hydrogenation of carvone

In this paper, a study on the hydrogenation of carvone by using Pt/Al2O3, P tSn/Al2O3, PtGe/Al2O3, Pt/C and PtSn/C is reported. TPR, Hz chemisorption, XPS and test reaction results show that the addition of a second metal to P t leads to important modifications of the structure of the metallic phase, though these modifications are different according to the nature of the sup port (Al2O3 or C). The activity and selectivity of these catalysts in carvo ne hydrogenation depend not only on the composition of the metallic phase, but also on the nature of the support. Thus, adding Sn or Ge to Pt/Al2O3 en hances the selectivity to unsaturated ketones (at a fixed carvone conversio n, X-carv = 1). When Pt is supported on activated carbon, small amounts of unsaturated alcohols are observed. The Sn addition to Pt/C sharply enhances the selectivity to carveol formation (the doubly unsaturated alcohol) reac hing values close to 100% at the initial stages of the reaction. (C) 2001 E lsevier Science B,V, All rights reserved.