Non-Siliceous Oxide Shells

The group extended this synthesis scheme to core-shell structures with different compositions using Au, Pd, and Pt as cores and CeOa, Ti02, and Z1O2 as shells [40, 41]. For instance, they encapsulated preformed Au NPs inside a porous ceria layer to yield Au Ce02 core-sheU NPs [40]. The core-sheU nanocatalyst with an Au loading of 1 wt% showed good activity under real preferential oxidation conditions 

3 Metal/Metal Oxide Yolk-Shell Nanocatalysts 

The yolk-shell nanostructure is a modified form of the core-shell configuration. The yolk-shell structure is distinguished from the core-shell structure in that the former has a hollow inner space between the core and the shell layers. Compared to 

The Co Si02 yolk-shell structure was obtained by thermal reduction of CoO Si02 core-shell particles via volume contraction of CoO to Co. The Co Si02 yolk-shell nanocatalysts exhibited high activity and reusability for phenoxycarbonylation of iodobenzene. In addition, the magnetic property of the cobalt cores permitted facile separation of the catalysts from the products. 

An alternative method to the yolk-shell structure is the use of a sacrificial intermediate layer, which is etched away to generate hollow spaces. This general scheme was realized by Schiith and his co-workers using the Au Zr02 yolk-shell NPs as an example (Fig. 5.11) [55]. They first synthesized 15-17 nm Au NPs using sodium citrate as the reductant, followed by coating a silica layer on the individual Au 

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