The activity of thermostable NiO/CeO2 heterointerface structure toward low-temperature catalytic CO–NO reaction

The surface grafting of NiO onto CeO2 nanocrystallites generates heterointerface structures, providing efficient active sites for CO–NO reactions toward forming N2 and CO2. In this study, we investigated the effects of high-temperature thermal aging on the activity and nanostructure of the NiO/CeO2 catalyst. After thermal aging at 900 °C, the catalyst retained a high catalytic activity, whereas the reference catalysts lost theirs owing to considerable solid-state reactions and sintering. The as-prepared fresh NiO/CeO2 catalyst (calcined at 600 °C) contained high dispersions of NiO species in CeO2 crystallites. Conversely, the thermally aged catalyst comprised grown NiO and CeO2 crystallites were allowed to contact intimately to form thermostable interfaces, where the perimeter in the vicinity provided the Ni2+-incorporated CeO2 surface for removing and filling the oxygen species in the catalytic cycle toward facilitating CO–NO reactions. Based on in situ Fourier transform infrared and parallel isotopic reaction analyses, we confirmed the following as possible pathways: (i) the removal of the surface oxygen by the adsorbed CO to form an oxygen vacancy (VO), (ii) the interaction between the adsorbed NO with VO, and (iii) the N–O bond cleavage and the reaction with CO to form isocyanate, followed by the reaction with NO to produce N2.