Reducing the size of metal nanoparticles down to the single-atom level has been actively pursued to maximize the use of precious metals. Recently, single-atom catalysts, in which all the metal atoms are isolated on a support with 100% dispersion, have received much attention. However, the lack of ensemble sites prevents valuable surface reactions that require metal proximity to occur. Here, we present metal (Pt, Pd and Rh) ensemble catalysts with 100% dispersion and a reduced metallic surface state. More specifically, nanoceria particles were anchored on Al-penta(3+) sites of activated gamma-alumina, and then metal was deposited and reduced. The ensemble catalysts are highly durable: their structure was maintained even after hydrothermal ageing at 900 degrees C for 24 h or after long-term reaction. These catalysts have superior activity and durability for three-way catalytic reactions and can provide insights beyond single-atom catalysts for heterogeneous catalysis.