Improving the Thermodynamic Stability of Aluminate Spinel Nanoparticles with Rare Earths

Surface energy is a key parameter to understand and predict the stability of catalysts. In this work, the surface energy of MgAl2O4, an important base material for catalyst support, was reduced by using dopants prone to form surface excess (surface segregation): Y3+, Gd3+, and La3+. The energy reduction was predicted by atomistic simulations of spinel surfaces and experimentally demonstrated by using microcalorimetry. The surface energy of undoped MgAl2O4 was directly measured as 1.65 ± 0.04 J/m2 and was reduced by adding 2 mol % of the dopants to 1.55 ± 0.04 J/m2 for Y-doping, 1.45 ± 0.05 J/m2 for Gd-doping, and 1.26 ± 0.06 J/m2 for La-doping. Atomistic simulations are qualitatively consistent with the experiments, reinforcing the link between the role of dopants in stabilizing the surface and the energy of segregation. Surface segregation was experimentally assessed using electron energy loss spectroscopy mapping in a scanning transmission electron microscopy image. The reduced energy resulted in coarse...