Most heterogenous metal catalysts consist of metal nanoparticles on a ceramic oxide support, but for systems that exhibit strong metal-support interactions (such as noble metals with cerium oxide), the maximum interaction might involve completely coating a metal nanoparticle with oxide. Yeung et al. have used a modified microencapsulation method, previously demonstrated for silica, for encapsulating platinum nanoparticles with ceria. Increasing the Pt loading from 1 to 5% created particles with larger Pt cores and thinner coatings of ceria. The thinnest coating (1.7 nm) increased the band transition for ceria from 3.18 to 3.33 electron volts, and increased the water-gas shift (WGS) activity (H2O 
CO 
H2 CO2) from negligible CO conversion for pure ceria to 63%. Unlike most other noble metal-ceria catalysts, these nanoparticles, which expose few noble metal sites, exhibit no activity for the competing reactions of methanation and higher hydrocarbon formation. -- PDS
J. Am. Chem. Soc. 10.1021/ja056102c (2005).
