WEB Correlative 3D-microscopy of Supported Catalytically Active Liquid Metal Solutions (SCALMS) using X-ray and electron tomographyWednesday (23.09.2020) 14:30 - 14:45 C: Characterization 1 Part of:
X-ray nano-tomography (Nano-CT) allows non-destructive 3D-investigations of materials across multiple length scales. The ZEISS Xradia 810 Ultra in Erlangen uses Fresnel zone plate optics to achieve 3D resolutions down to 50 nm and can be equipped with a Zernike phase ring enabling phase contrast in addition to standard absorption contrast. While the latter is utilized for imaging of materials containing regions of sufficiently different densities (i.e. containing elements with sufficiently different atomic numbers Z), the former can be employed to study weakly absorbing materials (low Z) and to discriminate materials exhibiting similar densities (similar Z). Due to its high-resolution capabilities and flexible imaging modes, the instrument is perfectly suited for scale-bridging correlative 3D studies of functional and structural materials in combination with Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) techniques [1,2].
We perform correlative 3D-studies of a Pd-Ga supported catalytically active liquid metal solutions (SCALMS) that are showing outstanding performance as catalysts for alkane dehydrogenation and, in particular, high resistance against coking.  SCALMS exhibit a complex material structure featuring a defined, catalytically active liquid film/droplet layer adsorbed on macro-porous silica templates. High-resolution 3D characterization across different length scales is required to reveal the complex pore morphology and the position of the catalytically active sites (Fig. 2c). Phase-contrast Nano-CT enables an independent 3D imaging of the metal droplets and the macro-porous silica network (Fig. 1b). Tomographic reconstructions enable non-destructive characterization of the 3D distribution of individual metal droplets inside the porous network structure (Fig. 1c). SEM imaging reveals Ga droplets on the surface of the porous silica support but does not allow to clarify to which extent Ga and Pd are incorporated in the bulk of the porous network .
The chemical composition of individual metal droplets inside the porous network can be characterized by site-specific Focused Ion Beam (FIB) sample preparation. Scanning TEM (STEM) imaging shows a single Ga droplet with the corresponding Energy-Dispersive X-ray Spectroscopy (EDXS) map revealing a bimetallic structure with Pd-rich and Ga-rich parts occurring in direct contact to each other (Fig. 2c) .