Precipitation vs. impregnation by ion-exchange

2 Precipitation vs. impregnation by ion-exchange Au precursors and the effect of the method of preparation and selected support on performance in selective epoxidation of propene over Au/Ti02 catalysts 

Au catalysts have received considerable attention recently because of the extraordinary performance in the low temperature oxidation of CO and high selectivities of over 99% in the direct epoxidation of propylene in the presence of hydrogen. Besides the extraordinary 

The preparation procedure was found crucial, in particular in relation to the effect on the OH population of the applied TiOa support. In photocatalysis, these OH-groups are essential for activity, in particular for conversion in organic phases. Hugon and coworkers have recently given an overview of impregnation procedures that might lead to improved catalysts. Here, we will further focus on the effect of preparation on the performance in epoxidation reactions. 

As stated, to obtain Au particles with a high selectivity, and stability, the preparation procedure and support appear to be of crucial importance. Furthermore, the morphology and composition of the support appear also of crucial importance, as is illustrated by the following. 

To evaluate the role of the support, the following catalysts were prepared. Degussa P25 (80% anatase, 50 m /g), was applied as the TiOg support for the 1 wt% Au-catalysts. TS-1 was synthesed either using tetraethyl orthosilicate (TEOS), TPA-OH (tetra-propylammo-nium hydroxyde, Aldrich) and TBOT (tetrabutylorthotitanate) (Catalyst TS-la), or SiOs particles (Degussa Aerosil) rather than 

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