Shape-shifting nanoparticles on a perovskite oxide for highly stable and active heterogeneous catalysis

Exsolution on perovskite oxides: morphology and anchorage of nanoparticles

“…Nanoparticle exsolution on perovskite oxides has been a ''hot topic'' and focus of extensive research for more than a decade. Ni, 28,[31][32][33]38,39,41,45,47 Co, 80 Fe, 67,74 Ru, 90,93 Ag, [95][96][97] Au, 100 Fe-Ni, 35,[49][50][51][53][54][55][56][57][58][59]62,64 Co-Ni, 83 Co-Fe, 75,77,[79][80][81][82][83][84] Fe-Re, 49 (Pr,Ba)O x 103 Ellipsoidal 23 Ni, 29,30,32,40,46 Co, 87,88 Fe, 69,72,73 Ru,…”

“…For instance, the shape of the catalytically active nanoparticles is crucial in heterogeneous catalysis, where depending on the reaction at hand, the presence of kinks or edges on a non-spherical particle might greatly influence the activity of a given catalyst. 45 That being said, the work by Kim et al 45 is the only one of 83 collected works that investigates this possibility in-depth with the goal of designing high performance catalysts. They used a (La,Ca)(Ni,Ti)O 3 host and investigated exsolved Ni particles, for the exsolution of which variations of reduction temperatures and durations were used.…”

“…Even though the shape (as well as the size) of a particle can affect the activity and/or the selectivity of a catalyst, 45 nanoparticle shape appears to mostly be a rather inconsequential descriptor of the exsolved nanoparticles. By far the most commonly observed are spherically shaped particles (42 publications), with ellipsoidal particles reported with only half the frequency of spherical ones (23).…”

“…by SEM): nanoparticles sizes (of at least one specific type) are given in almost all publications collected for this article (with the exception of 5), whereas the population density is reported in only 22 out of 83 studies. The particle shape, on the other hand, is rarely reported expressly and hardly ever the main topic of investigation (with the notable exception of a study of Kim et al 45 – see Section 3c). However, it can usually be derived from electron microscope images, given proper image quality.…”

“…Wang et al 40 found different population densities for different B-site dopants (Co, Ni, and Cu, respectively) under otherwise similar conditions. Other factors include applied voltage during electrochemically driven exsolution (Fan et al , 22 larger voltage leads to increased population density), oxygen partial pressure during water driven exsolution (Kim et al , 97 higher pressures increase the density), preparation method (Sun et al , 45 the thermal shock method leads to a significantly larger density), or number of atomic layer deposition cycles (Joo et al 35 deposit Fe 2 O 3 on the investigated samples to form Fe–Ni alloy nanoparticles after an additional reduction step and find that more deposition cycles lead to higher particle numbers per unit area, with the particle size, however, remaining rather similar).…”