High entropy oxides: New superior supports for single atom catalysts

Single Atom catalyst (SAC), a new frontier in heterogeneous catalyst design has evolved as a novel strategy to resolve the cost puzzle hindering the commercial scale applications of benchmark noble metal catalysts in various technologies. Downsizing expensive noble metal catalyst to atomically active centers have simultaneously reduced cost via enhanced atom utilization and maximized their catalytic activity and selectivity. However, taking full advantages of this novelty requires stabilization on appropriate support materials that provide adequate anchoring sites, promote strong metal support-interaction, ensure adequate stabilities to withstand extreme chemical or thermal reaction conditions, and favorably modulate their electronic structures for optimal performance. High entropy oxides (HEOs), characterized by unusual synergistic effects, highly reducible surface lattice oxygen, and high thermal and chemical stabilities, have recently emerged as a new type of support for SACs with superior performances. Despite their immense potential to reinvent the heterogenous catalyst design, single atoms supported on HEOs have not received adequate attention. Herein fundamental aspects regarding HEOs such as their discovery, design rules, stabilization criteria, computater aided design, and emerging synthesis approaches suitable for catalytic applications have been presented in this review. We also provide a detailed perspective of the SACs/HEO domains, highlighting their synthesis, entropy-driven properties, catalytic performance, and stabilities during thermochemical processes at elevated temperatures. Although high entropy materials have been highlighted in a few recent reviews, this review is the first strictly exclusive to single atoms supported on HEOs.