Visible light enhanced thermocatalytic CO + NO reaction over metastable NiCo2O4 catalyst

A NiCo 2 O 4 catalyst was evaluated for CO + NO reaction under a photo-thermal synergistic effect. Compared with crystalline samples, metastable NiCo 2 O 4 with a crystalline/amorphous heterostructure exhibited higher catalytic activity due to its better low temperature reducibility and more oxygen vacancies (VOs). The collective TPR, XPS, and in-situ DRIFTS results revealed that more VOs induced by CO directly interacting with the lattice oxygen of NiCo 2 O 4 could promote NO adsorption and activation, and visible light irradiation further reinforced the above processes by facilitating CO to capture lattice oxygen and enriching electrons in VOs. With the increase in reaction temperature, the electron-rich VOs could further drive NO dissociation into N 2 . Herein, the VOs was not only an active center of catalytic reaction, but also acted as a bridge between CO and NO for lattice oxygen circulation. Thus, a photo-thermal synergistic effect for NO reduction by CO occurred over metastable NiCo 2 O 4 . A photo-thermal catalytic process for CO + NO over NiCo 2 O 4 was proposed as above. At low temperature, CO would react with surface lattice oxygen of catalyst to generate VOs, which promoted the NO adsorption and activation. While visible light irradiation further reinforced the above process by facilitating CO to capture lattice oxygen and enriching electrons in VOs. With the increase in reaction temperature, the formed VOs with enriched electrons drove successively the transformation and dissociation of NO into NO x , N 2 O, and then finally N 2 . • Metastable NiCo 2 O 4 sample was composed of crystalline and amorphous. • Metastable NiCo 2 O 4 exhibited a better catalytic performance for CO + NO reaction than the crystalline NiCo 2 O 4 counterpart. • Metastable NiCo 2 O 4 owned a better low-temperature reducibility to form more oxygen vacancies (VOs). • Photo-excitation of NiCo 2 O 4 could promote CO to be trapped in its lattice oxygen and result in more VOs formation. • Electron-enriched VOs facilitated the adsorption and dissociation of NO, resulting in an accelerated NO reduction.