A dual-site approach in high-entropy oxide aerogels creates active and selective reverse water–gas shift catalysts

Abstract

High-entropy oxides consist of 4 or more equimolar or near-equimolar elements stabilized in a crystalline phase. The inherently slow atomic diffusion in these materials holds promise for creating sinter-resistant high-temperature catalysts, but most reported synthetic methods create multi-metal materials with low surface area. Here, we introduce high-entropy rare-earth oxide aerogels (HERAs) as a route to unlock the nearly unlimited compositional versatility of high-entropy oxides in an architected nanostructure with high surface area (>130 m² g^-1). We demonstrate that a base oxide composition of (YZrCeHf)Ox readily hosts catalytically relevant transition metals (Ni, Co, Fe) to effectively catalyze the reverse water–gas shift (RWGS) reaction: CO₂ + H₂ → CO + H₂O. A high-entropy composition comprising 2.5 at.% Ni and 20% Fe in (YZrCeHf)Ox aerogel is an exceptionally active, selective, and stable catalyst, with no loss of CO₂ conversion over 90 h at 500°C and no CH₄ byproduct detected.