Preparation of nanostructured Pd particles using a seeding synthesis approach - Application to the selective hydrogenation of buta-1,3-diene

Well-defined nanostructured Pd particles were successfully synthesized in aqueous solution using a seeding-mediated approach with cetyltrimethylammonium bromide (CTAB) acting as both capping and structure-directing agent. Four well-defined nanoobjects were obtained: nanocubes, nanotetrahedra, nanopolyhedra, and nanorods. The anisotropic Pd nanorods exposed preferentially {1 0 0} facets due to the stabilization effect of CTAB. After deposition onto alpha-Al2O3, these nanostructured Pd particles were tested in the selective hydrogenation of buta-1,3-diene at 298 K under 20 bars of H-2. Compared to an isotropic Pd catalyst, anisotropic Pd catalysts were found highly selective for the hydrogenation of buta-1,3-diene into butenes without further hydrogenation into butane. Moreover, on the nanostructured catalysts, further hydrogenation of but-1-ene into butane is reduced while but-2-enes were hardly converted. Finally, an unusual high level of cis but-2-ene isomer was observed. These results suggest a modification of the mechanism usually admitted for Pd catalysts when a well-defined nanomorphology is achieved. (c) 2007 Elsevier B.V. All rights reserved.