Abstract text (incl. figure legends and references)

Nanoparticles are widely used for catalytic applications. Their catalytic properties are largely defined by their size, shape, and surface chemistry. In general research is focused on small particles or, in recent years, even on single atoms. However, their synthesis is often complicated, involves toxic and expensive chemicals and the amount that can be produced is limited. Moreover, the particles themselves may pose a threat to the environment when they leak into fresh water as their size makes them difficult to filter.
Instead of using single nanoparticles, an alternative way is to employ highly porous materials for catalysis. Like nanoparticles, they exhibit enormous surfaces which provide active sites for catalytic reactions. Moreover, they are bulky and are therefore much easier to handle than nanoparticles. In many cases, however, only the first few surface-near pores are available for the catalytic reaction. Deeper pores are hardly accessible to educts and products due to kinetic transport limitations.

The aim of this work is to produce larger (up to 2 µm) nanostructured metallic and metal-oxide particles that contain pores in the range of a few tens of nanometers. This way, the advantages of using particles and porous systems are combined as they are on the one hand small enough to be accessible from all sides while on the other hand are large enough to be handled easily. The pores in the materials used for this work are first produced by using a well-known controlled oxidation process called dealloying where a less noble component of a metallic solid solution is leached out in an acid bath. At the same time, the more noble component forms a bi-continuous open pore network. This process is well-established for noble elements like Au and Pt. Recently, transition metals (Cu, Ni, etc.) have come into research focus as cheaper alternatives. The Cu particles used in this work are produced by first dealloying a bulk Cu0.3Mn0.7 alloy in HCl or H2SO4 to form the porous network with pore sizes between 10-100 nm followed by sonication to break down the porous structure into smaller fragments. The resulting particles are complex in shape and highly porous (fig. 1, TEM bright field image). The size of the porous particles ranges between 200 nm and 2 µm. After fabrication, the reactive Cu particles can further be modified or functionalized. By a simple and controlled oxidation process in air, core-shell particles with a defined oxide layer can be produced, whereas fully oxidized particles form a hollow-core structure (fig. 2, HAADF-STEM image).
In order to employ such particles for catalytic applications, it is necessary to reveal the complex structure along the formation process of the Cu particles as well as their respective oxides in a three-dimensional manner. Therefore, tomography in scanning transmission electron microscopy mode has been performed at different stages of the preparation route. To prove the nature of the oxidation state of the Cu, electron energy loss spectroscopy was performed.
Moreover, small amounts of Mn below 1 at% can still be found in the fully processed particles by energy dispersive X-ray spectroscopy. It is envisioned that the remaining Mn(-oxide) can act as a dopant in the particle boosting its catalytic performance. Therefore, first tests are planned to evaluate the catalytic behavior of those particles at different oxidation conditions.