Nanoisozymes: The Origin behind Pristine CeO₂ as Enzyme‐mimetics

It is well‐known that the interplay between molecules and active sites on the topmost surface of solid catalyst determines its activity in heterogeneous catalysis. The electron density of active site is believed to affect both adsorption and activation of reactant molecules at surface. Unfortunately, commercial X‐ray photoelectron spectroscopy (XPS) often adopted for such characterization is not sensitive enough to catalyst’ topmost surface. In our opinion, most researchers fail to acknowledge this point during their catalytic correlation, leading to different interpretations found in literatures over the past decades. Recent studies on pristine Cu₂O (Nat. Catal. 2019, 2, 889; Nat. Energy 2019, 4, 957) have clearly suggested that the electron density of surface Cu is facet dependent and plays a key role in CO₂ reduction. Herein, we show that pristine CeO₂ can reach 2506%/1133% increase in phosphatase‐/peroxidase‐like activity once the exposed surface is wisely selected. Using nuclear magnetic resonance (NMR) with surface probe, the electron density of surface Ce (i.e. the active site) is found facet‐dependent and the key factor dictating their enzyme mimicking activities. Most importantly, the surface area of those CeO₂ morphologies was demonstrated to become a factor only when their surface Ce can activate the adsorbed reactant molecules.