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This study reveals the essential role played by surface oxygen vacancies in catalytic oxidation reactions, and complements the common viewpoint that Co3+ is the major activity species in Co3O4-based systems.

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Crystal facet engineering (CFE) has been widely employed to regulate the photoreactivity of crystalline materials, mostly concerning the surface atomic and electronic structures. However, surface defects ubiquitous in real catalysts have long been less recognized. An integrated examination of various influence factors is necessary for the elucidation of an accurate structure–function relationship. Herein, we carefully studied the heterogeneous photoreactivity of CeO2 nanocrystals (NCs) with well-defined crystal facets in multiple processes, including photocatalytic oxidation of volatile organic compounds (VOCs), O2 evolution, and ·OH generation. Variable reactivity priorities were found between different nanoshapes as well as samples of identical nanoshapes. With integrated examinations of the coexisting surface factors (i.e., atomic, electronic, and defect structures), surface defects were evidently proved to compete with other surface factors in deciding the final photoreactivity orders. Surface-defect structure (e.g., Ce3+ ions and O vacancies) was suggested to greatly influence the surface properties of ceria NCs, including the activation of reactants as well as the mobility of surface lattice oxygen. The results clearly confirm the surface-defect dependence of photoreactivity and provide further insights into the complex surface effects in semiconductor photocatalysis. It also underscores the significance of surface-defect structure as an essential supplement to the traditional CFE strategy for achieving desired solar energy utilization.

Photocatalytic water splitting is the most promising process to convert solar energy into high purity chemical fuel (hydrogen), which has received significant attention in recent years. Only several photocatalysts have been reported in the literature for pure water splitting under visible light. Herein we report for the first time quantum sized BiVO4 can decompose pure water into H2 and O2 simultaneously under simulated solar light irradiation without any cocatalysts or sacrificial reagents. By electrochemical measurement, we demonstrate that the significantly different photocatalytic activity of the quantum sized BiVO4 arises from the negative shift of conduction band edge by a quantum confinement effect and a decreased overpotential for water reduction. Although the generated H2 and O2 are nonstoichiometric in the present study, these findings establish the great potential of using quantum sized BiVO4 photocatalyst and solar energy for overall water splitting.

Supported precious metals with atomic dispersion are of great interest in catalysis due to their potentials in achieving maximum atom efficiency and unique reactivities. Herein, the active sites for low-temperature CO oxidation are elucidated over single-atom Pd1/CeO2 catalysts prepared via high-temperature atom trapping (AT). The increased oxygen vacancies on CeO2 surface induced by 800 °C air calcination result in decreased Pd–CeO2 coordinations, i.e., the coordination-unsaturated Pd2+ on CeO2. Light-off and light-out measurements coupled with CO-DRIFTS and X-ray absorption characterization confirm that these coordination-unsaturated Pd2+ on CeO2 are much more reactive than the fully coordinated counterpart, evidenced by a decrease of T 90 (temperature to achieve 90% conversion) by ∼100 °C in CO oxidation at a gas hourly space velocity of 300 L g–1 h–1.

Half reactions of CO 2 RRElectrode potentials E 0 (V vs SHE, pH 7) CO 2 + e − →*CO 2 δˉ− 1.9 CO 2 + 2H + + 2e − →CO −0.52 CO 2 + 2H + +2e − →HCOOH −0.61 CO 2 + 4H + + 4e − →HCHO −0.51 CO 2 + 6H + + 6e − →CH 3 OH −0.38 CO 2 + 6H + + 8e − →CH 4 −0.24 CO 2 + 12H + + 12e − →C 2 H 4 −0.34 2H + + 2e − →H 2 O −0.42

As ingle-atom Pt 1 /CeO 2 catalyst formed by atom trapping (AT, 800 8 8Ci na ir) shows excellent thermal stability but is inactive for CO oxidation at lowt emperatures owing to over-stabilization of Pt 2+ in ah ighly symmetric square-planar Pt 1 O 4 coordination environment. Reductive activation to form Pt nanoparticles (NPs) results in enhanced activity;h owever, the NPs are easily oxidized, leading to drastic activity loss. Herein we showthat tailoring the local environment of isolated Pt 2+ by thermal-shock( TS) synthesis leads to ah ighly active and thermally stable Pt 1 /CeO 2 catalyst. Ultrafast shockwaves (> 1200 8 8C) in an inert atmosphere induced surface reconstruction of CeO 2 to generate Pt single atoms in an asymmetric Pt 1 O 4 configuration. Owing to this unique coordination, Pt 1 d+ in ap artially reduced state dynamically evolves during CO oxidation, resulting in exceptional low-temperature performance.C Oo xidation reactivity on the Pt 1 /CeO 2 _TS catalyst was retained under oxidizing conditions.