Stimuli induced transformations of confined matter

The control of the transformations of confined soft and hard matter, upon embedding in nanoporous media, through external stimuli such as temperature, electric fields and light plays an increasingly important role in the fundamental condensed-matter and applied materials sciences. Besides hydrogen production, the surplus electric and solar power can be used to develop power-to-X and solar-to-X approaches to manipulate matter for the development of devices (e.g. heterogeneous catalysts, actuators, sensors) that adapt their structure and function to changes in their environment. To achieve this, clear understanding of the structural modifications of matter in confinement and thus in interface-dominated geometries needs to be reached. The proposed project intends to investigate transformations at the nanoscale of guest species and of respective hosting matrices (e.g. ionic segregations, phase transitions) driven by external stimuli such as temperature, light and electric fields combining anomalous small and wide angle X-ray scattering (ASAXS/AWAXS) and X-ray absorption spectroscopy (XAS) at the P62 beamline of PETRA III. For this purpose, a dedicated sample environment will be developed integrating three sample cells for powder and monolithic samples conditioned at different temperatures (up to 1000 °C), gas atmospheres, electric potentials and UV-visible light exposure. Therefore, aside from the in situ study of stimuli-induced transformations, the planned infrastructure suits well to perform also operando experiments ideal for catalysis, energy storage applications and for functional materials with integrated switchable effective properties, e.g. switchable light absorption or color.

Herauslösen von Metallnanoteilchen aus mesoporösen Perowskitoxiden

In heterogeneous catalysis, it is well-known that the surface area of the support and its interaction with the metal catalyst cover a pivotal role. Exsolution has been recently proposed as a novel synthesis strategy for supported metal nanoparticles catalysts, which are strongly anchored to the support and can be self-regenerated. Metal nanoparticles are here obtained via surface segregation of transition metal dopants from a perovskite oxide upon high-temperature oxygen release. So far, this approach has been applied to non-porous sintered structures. In the present proposal we aim to investigate the exsolution process of Fe, Co, Ni from mesoporous parental perovskite oxides of type La0.2Sr0.8Ti1 xMxO3 (LSTM, where M = Fe, Co, Ni and 0.05 ≤ x ≤ 0.2) in order to prepare advanced metal-supported catalysts. We intend to tune particle morphology by controlling the oxygen release not only through tuning process time, temperature, and gas atmosphere, but also varying a hitherto unexplored parameter as the nanoporosity of the matrix. Furthermore, we aim to investigate the metal-support interactions, as well as the mechanism of nanoparticle regeneration, so far known only for sintered exsolved systems. Precise and comprehensive assessment of the exsolved nanoparticle formation, stability against agglomeration, and regeneration will be studied for the first time using standard and anomalous small-angle X-ray scattering techniques, going beyond the limits of electron microscopy methods adopted so far. The catalytic properties of mesoporous exsolved materials with respect to the CO2 methanation reaction will be tested

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