Carbon-bridged atomically dispersed platinum on MOF-derived ZnO/C for selective photocatalytic oxidation of NO into Nitrates and Nitrites

Abstract

Using nanoclusters and single atoms with unique activity to replace nanoparticles is a promising strategy to enhance catalyst activity. However, stable loading of nanoclusters and single atoms remain a challenge. This paper reports atomically dispersed Pt bridged with metal-organic framework (MOF)-derived ZnO/C through carbon atoms (Pt–ZnO/C), by impregnation combined with calcination, for photocatalytic oxidation of NO. The MOF-derived ZnO/C has a larger specific surface area than pure ZnO. The presence of C enhances the visible light absorption, promotes the migration of photogenerated carriers, and more importantly facilitates the stabilization of Pt single atoms through Pt–C interactions. The Pt species present in the Pt–ZnO/C catalysts in the form of single atoms and nanoclusters. The Pt–ZnO/C catalysts show high NO conversion rates and selectivity towards NO3−/NO2− ions formation. Specifically, the NO conversion rate of 81.9% is much higher than those of ZnO/C (31.4%) and Pt nanoparticles loaded ZnO/C (Pt NPs-ZnO/C, 58.6%). In addition, the selectivity of NO3−/NO2− (i.e., 98.6%) formation over the Pt–ZnO/C catalyst is much higher than that of NO2 (i.e., 1.4%). Furthermore, the photocatalysis tests and ESR results suggest that the Pt single atoms and nanoclusters can enhance the oxidation of NO by promoting the production of O2•- and OH•. The DFT results also reveal that single Pt atoms promote the adsorption of O2 and H2O to form O2•- and OH•. More importantly, OH• can promote the selective oxidation of NO to NO3−/NO2− ions. In addition, the projected density of states of single Pt atoms loaded on the ZnO/C catalysts show that the presence of C atom bridge favors the stability of single Pt atoms because of the interaction between C and Pt atoms. This work provides a new strategy for the design of single-atom-loaded metal oxide catalysts.