A General Mechanism for Stabilizing the Small Sizes of Precious Metal Nanoparticles on Oxide Supports

We recently discovered that MgAl2O4 spinel (111) nanofacets optimally stabilize the small sizes of platinum nanoparticles even after severe high-temperature aging treatments. Here we report the thermal stabilities of other precious metals with various physical and chemical properties on the MgAl2O4 spinel (111) facets, providing important new insights into the stabilization mechanisms. Besides Pt, Rh, and Ir can also be successfully stabilized as small (1-3 nm) nanoparticles and even as single atomic species after extremely severe (800 degrees C, 1 week) oxidative aging. However, other metals either aggregate (Ru, Pd, Ag and Au) or sublimate (Os), even during initial catalyst synthesis. On the basis of ab initio theoretical calculations and experimental observations, we rationalize that the exceptional stabilization originates from the epitaxially matched structure, i.e., lattice matching in geometry and the correspondingly strong electronic attractions at interfaces between the spinel (111) surface oxygens and epitaxial metals/metal oxides. On this basis, design principles for catalyst support oxide materials that are capable of stabilizing precious metals are proposed.