Nanoscale (111) faceted rock-salt metal oxides in catalysis

Facet-specific growth is highly desirable for catalysts, as conversion and selectivity can be altered with increasing amounts of particular active sites. The (100) surface of a rock-salt structure is comprised of alternating oxygen anions and metal cations, similar to the (110) facet. The (111) surface differs substantially in that an ideal (111) surface would consist solely of oxygen anions or metal cations, and cannot exist as-is. However, wet chemical syntheses of MgO(111) and NiO(111) have recently been reported; theory and experiments show the (111) surface is stabilized as a hydroxylated surface. These (111) faceted metal oxides exhibit catalytic properties that differ significantly from their (100) counterparts. Here, we discuss the theory and performance of the (111) rock-salt metal oxides in catalysis, as supports, and as adsorbents.