Search

This study investigated the redox exsolution of Ni nanoparticles from a nanoporous La0.52Sr0.28Ti0.94Ni0.06O3perovskite. The characteristics of exsolved Ni nanoparticles including their size, population, and surface concentration were deeply analyzed by environmental scanning electron microscopy (ESEM), transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDX) mapping, and hydrogen temperature-programmed reduction (H2-TPR). Ni exsolution was triggered in hydrogen as early as 400 °C, with the highest catalytic activity for low-temperature CO oxidation achieved after a reduction step at 500 °C, despite only a 10% fraction of Ni exsolved. The activity and stability of exsolved nanoparticles were compared with their impregnated counterparts on a perovskite material with a similar chemical composition (La0.65Sr0.35TiO3) and a comparable specific surface area and Ni loading. After an aging step at 800 °C, the catalytic activity of exsolved Ni nanoparticles at 300 °C was found to be 10 times higher than that of impregnated ones, emphasizing the thermal stability of Ni nanoparticles prepared by redox exsolution.

The direct decomposition of NOxat moderate temperatures is a challenge because of the poisoning of the surface of noble metals by oxygen, yet the modification of Pd with Au enables obtaining a highly stable catalyst under an O2-free feed at 450 °C. Care was taken to ensure that the reaction was not due to the reduction of NOxwith carbonaceous residues by monitoring CO2evolution. Pd–Au alloyed domains with a wide range of compositions were evidenced by in situand ex situXRD, the Pd content of which decreased with the increasing oxidising nature of the feed due to phase segregation giving rise to PdO and an Au-rich alloy. Under air, the limiting alloy composition was Pd0.2Au0.8. The catalyst was yet inactive in the presence of 5% O2.