High-Temperature Stable Metal-Silica Core-Shell and Yolk-Shell Materials with Exceptional Dimensional Control

The controlled synthesis of nanomaterials holds great promise for the design of highly efficient catalysts. However, the low stability of nanoparticles poses a severe limitation on the use of such materials in many industrial applications. This limitation is motivating efforts to stabilize nanoparticles via embedding or encapsulation in nanostructured matrix materials. The main challenges thereby are the control over key material dimensions and accessibility to the nanoparticle via porosity of the matrix.

We are presenting results of different types of metal-silica core-shell nanomaterials with highly controllable size and shape. The materials are synthesized in a one-pot reverse microemulsion-templated approach. By adjusting the synthesis parameters, the structure of the core-shell materials can be changed from solid (but porous) core-shell structures to spherical “yolk-shell” structure with a pronounced cavity, to strongly elongated, rod-shaped structures with high aspect ratios. Furthermore, the thickness of the silica shell can be adjusted with nanometer-size precision. In this way, we have been able to synthesize nickel-, copper-, iron- and palladium-based metal-silica core-shell materials.

Electron microscopy (TEM) demonstrates overall core-shell particles sizes of 20 nm – 50 nm with adjustable silica wall thickness of 3-20 nm, encapsulating metal cores with size from sub-nanometer clusters to nanoparticles with ~10 nm diameter. The porosity of the silica walls is confirmed via CO chemisorptions and complete oxidation and reduction of the metal nanoparticle in TPO/TPR. Remarkably, the materials are thermal stable up to at least ~800°C, without significant changes in morphology.