Chemistry

A Precatalytic Cycle

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Science  16 Apr 2010:
Vol. 328, Issue 5976, pp. 287
DOI: 10.1126/science.328.5976.287-b

When metal particles are deposited or formed on oxides for catalytic applications, the goal is to create small clusters that expose as many surface atoms as possible. One method of limiting surface adsorption is atomic layer deposition, which restricts deposition by requiring the system to undergo cycles of stoichiometric reactions. For the formation of palladium (Pd) particles on silica gel supports, Lu and Stair report a cycle of three reactions that occur at low temperatures (below 110°C) and yield highly uniform particles with an average size of 1 nm. Pd is deposited on a limited number of surface sites as an ion complex, coordinated by hexafluoroacetylacetonate ligands. A second step deposits an alumina or titania precursor, and a third step adsorbs water in order to form the oxides. This cycle is repeated over as many as 15 cycles, and then the protective Pd ligands are removed by reaction with formalin at 200°C. CO chemisorption studies showed that successive cycles do not interfere with the accessibility of the Pd clusters to reactants.

Angew. Chem. Int. Ed. 49, 2547 (2010).

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