(374b) From Embedded to Supported Metal/Oxide Nanomaterials: Thermal Behavior and Modelling of Structural Evolution At Elevated Temperatures

The relation between structure and function is of major importance at material interfaces which often excel in terms of chemical or physical effects. Therefore, multi-phase nanocomposites (e.g. core-shell, janus-shaped and carrier-supported nanoparticles) attract attention due to their possibility to contact two materials at the nanometer scale profiting from their highly increased interaction area.

Especially at metal/oxide interfaces, accounting for a majority of heterogeneous catalysts, the structure-function relationship has been studied intensively. High temperature, dry aerosol processes (flame spray synthesis) are common for building such composites. But the formation of key structural elements in such multi-component systems, depending on coagulation-order and solid-solid diffusion, is not fully understood.

Here, we present the synthesis of silica coated crystalline Pd nanoparticles (Pd in silica) in a single step flame spray pyrolysis process. The nanometer scale transformation of this core-shell material to nanocrystalline Pd supported on the amorphous silica matrix (Pd on silica) was achieved at temperatures exceeding 700°C. A physical, population balance based aggregation/diffusion model gives an understanding of the influence of temperature, matrix viscosity, particle sizes and concentrations on this transformation process. It enables morphological predictions (core-shell vs. carrier-supported particles) in nanocomposite formation processes such as flame spray synthesis. It further allows to understand the performance of multi-phase materials during thermal cycling in catalysis or fuel cells.

Figure 1. Morphological transformation of noble metal encapsulated in oxide (core-shell, left TEM image) nanoparticles to supported on oxide particles (right TEM image).

Reference :

S. Bubenhofer et al., J. Phys. Chem. C, 115(4), 1269-76 (2011).