EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Perovskite-type oxides (ABO3) systems were recently proposed for the in situ growth of metal supported nanoparticles as novel high performing catalysts in heterogeneous catalysis. Perovskites possess the ability to easily incorporate catalytically active dopants forming AB1−xMxO3‑δ compositions. Subsequent exposition to reducing atmospheres (Ar/H2) at high temperatures (≈ 900 °C) these metal dopants Mn+ are reduced and exsolved as highly dispersed nanoparticles strongly socketed in the perovskite oxide support. Nanostructuring represents a method to improve exsolution kinetics exploiting the smaller crystallite sizes and hence the shorter diffusion paths for charge carriers. In this way, faster nanoparticle growth at lower temperatures and higher catalytic reactivity are expected. Although nanoparticle exsolution is extensively studied, to the best of our knowledge, the effect of nanostructuring was poorly investigated so far.
To study this concept the exsolution of Ni nanoparticles was examined for highly dense and nanoporous La0.52Sr0.28Ti0.94Ni0.06O3 (LSTN), with specific surface area of 30 m2/g. Reductions were performed from 900 °C down to 500 °C to thoroughly investigate the exsolution process. In comparison to sintered LSTN, exsolved Ni particles in nano-LSTN formed already at 500 °C. The early occurrence of the reduction process was demonstrated by H2-TPR experiments, in situ electron microscopy, synchrotron XRD and X-ray absorption spectroscopy (XAS) studies. Nanostructured LSTN displayed small nanoparticles of ca. 15 nm whereas in the sintered counterparts their size was ca 50 nm. We found that the reduction process of Ni in nanostructured perovskites occured 200 °C earlier than in sintered materials without any loss of porosity during exsolution.
Biogas dry reforming tests showed the superior catalytic performance of exsolved Ni from nanostructured LSTN. CH4 and CO2 were converted above 70% and found 7 times and 2 times higher with respect to sintered systems and commercial Ni/Al2O3 catalysts, respectively.
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