Preparation of the Pd nanowires and Pd porous nanoballs via CVI (chemical vapor infiltration) and their catalytic effects

Abstract

Novel matrix free palladium based nanoballs and nanowires as well as palladium superlattices and wires encapsulated inside of mesoporous matrices cubic MCM-48 and hexagonal SBA-15 was synthesized. In the synthesis of the Pd anostructures, the shape and size are precisely controlled with pore scales under 10 nm. The metal-organic precursor, $Pd(hfac)_2$ is sublimed into the mesoporous silica via chemical vapor infiltration (CVI); These experiments constitute the first demonsration of shape- and size-controlled matrix free Pd nanostructures via a low temperature mesoporous template-assisted process; this low temperature CVI approach makes possible the synthesis of various metallic nanoporous and nanostructured materials. Introducing of nucleation sites into the mesoporous materials makes metal highly dispersed pattern. The results of this investigation are probably helpful for developing the efficient metal-mesoporous catalyst sytem. Especially, ball shaped palladium nanocatalysts in an MCM-48 matrix (Pd@MCM-48) with unique structural features and they provided decent selectivity in hydrogenation of various olefins and, furthermore, unprecedented complete hydrogenolysis selectivity of a benzylether before hydrogenation of a double bond occurred. This Pd catalyst system is air stable and reusable by filtration and can be extended to other types of organic reactions. In addition, the unique selectivity of these kinds of nanostructured catalysts might have practical utilities in organic synthesis