Cortex-catalysts

Reetz et al. have used N-(octyl)4Br-stabilized Pd colloids (typical size, e.g., 3nm) as precursors to form so-called cortex-catalysts, where the active metal forms an extremely fine shell of less than lOnm on the supports (e.g., AI2O3). Within the first 1-4 s, the impregnation of AI2O3 pellets by dispersed nanostructured metal colloids leads to the time-dependent penetration of the support which is complete after 10 s. Cortex catalysts were reported to show a threefold higher activity in olefin hydrogenation than conventionally prepared catalysts of the same metal loading (5% Pd on AI2O3) [388]. 

Reetz, M.T., Quaiser, S.A., Breinbauer, R., and Tesche, B., A New Strategy in Heterogeneous catalysis the design of cortex catalysts/catalysis/clusters/ immobilization/ surface chemistry, Angew. Chem. Int. Ed. Engl., 34, 2728,1995. 

FIGURE 6.18 Heterogeneous Pd colloid catalysts of the cortex-type (adapted with permission from Reference 187) (a) AI2O3 pellets (3.2 mm) after penetration with a 0.5 M solution of (octyl)4NBr stabilized colloidal Pd in THF for 1 s, (b) for 4 s, (c) for 10 s. 

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