Clean Technology 2011

Self-Assembly Synthesis of Heterogeneous Catalysts with Novel Nanoarchitectures and Improved Selectivities (invited presentation)

F. Zaera
University of California, US

Keywords: nanocatalysts, self-assembly, shape selectivity, yolk@shell, dendrimers


Self-assembly, in particular colloidal and sol-gel procedures, has been used to prepare heterogeneous catalysts with novel architectures. In one case, catalysts consisting of dispersed platinum metal particles with narrow size distributions and well-defined shapes were prepared in three stages: (1) synthesis of tetrahedral and cubic colloidal metal particles in solution (size and shape could be controlled independently this way); (2) dispersion of the colloidal particles onto high-surface-area solids, by in-situ reduction of the colloidal mixtures in the presence of the support, by in-situ sol-gel synthesis of the support in the presence of the colloidal particles, or by direct impregnation of the particles on the support; and (3) activation of the resulting catalysts for the promotion of carbon-carbon double-bond cis-trans isomerization reactions in olefins. It was shown that the selectivity of that reaction could be controlled by using supported catalysts with appropriate metal particle shapes, in particular tetrahedral particles with (111) facets exposed. Three additional catalyst architectures will be briefly presented as well: (1) metal supported catalysts made by using dendrimers as scaffolding structures to prepare small platinum nanoparticles of well-defined sizes; (2) nanocrystalline metal catalysts first dispersed on the surface of support materials such as silica colloids and then covered on a freshly grown layer of porous silica in order to physically fix their positions and minimize sintering; and (3) yolk@shell metal-semiconductor constructs for photocatalytic applications where the metal particles are placed inside a semiconductor shell in order to enhance charge separation upon photoactivation while limiting the diffusion of gas to the metal surface to minimize H2+O2 recombination.

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