Single Atom and Nanoclustered Pt Catalysts for Selective CO2 Reduction

Increasing CO2 emissions into the environment has triggered intensive research on CO2 capture and utilization. Downsizing catalyst nanoparticles (NPs) to an atomic dispersion, exposing all atoms as active sites on the surface, is highly desirable to reduce noble metal usage and see improved activity on many catalytic reactions such as CO oxidation and CO2 reduction. Yet, current studies on atomic-level understanding of the catalytic CO2 reduction mechanism are poorly understood. Here, we report the synthesis of CeO2 NPs decorated with atomically dispersed Pt atoms and scrutinize the reaction mechanism of CO2 reduction catalyzed by single atom (0.05 wt %) Pt/CeO2 and nanoclustered (2 wt %) Pt/CeO2 using in situ DRIFTS. The activity results indicate that the single atom Pt/CeO2 exhibited a 7.2 times higher reaction rate, despite having a 40 times lower Pt loading than for the nanoclustered Pt/CeO2 catalyst, and possessed good thermal stability at 500 °C. In situ spectroscopy demonstrated that CO2 activation occurs on the oxide support while H2 dissociation occurs on the Pt metal. The single atom or nanoclustered nature of the Pt catalyst impacts on the selectivity of the reaction products toward CO or CH4, whereby different mechanistic pathways for CO2 reduction are suggested based on the geometric Pt arrangement. The isolated Pt atom geometry, unlike nanoclustered Pt with continuous Pt–Pt bonds, weakly binds CO which restricts further hydrogenation and prevents CO poisoning. The findings illustrate the unique opportunities available for tuning catalyst activity and chemoselectivity by the rational design of atomically dispersed catalysts.