PdAg alloy nanoparticles encapsulated in N-doped microporous hollow carbon spheres for hydrogenation of CO2 to formate

Abstract

Here, we report a general synthesis approach to produce PdAg nanoparticles (NPs) that are dispersed uniformly within N-doped microporous hollow carbon spheres (NMHCS) for hydrogenation of CO2 to formate. The optimized PdAg@NMHCS catalyst, which was obtained by using an optimized amount of ethylenediamine as the nitrogen source and pyrolyzed at 500 °C, exhibits extraordinary activity for CO2 hydrogenation to formate, showing a high turnover number (TON) of 640 and 2750 at 100 °C after 2 and 24 h, respectively. Experiments reveal that different carbonization temperatures cause changes in the surface area, the nitrogen content of NMHCS, PdAg NPs dispersion, and the formation of Pd-N bonds. Upon consideration of kinetic analyses, N-doped MHCS are not only effective for the adsorption of CO2 due to the doping of nitrogen but also would reduce the activation energy barrier for CO2 hydrogenation to formate by facilitating including CO2 adsorption/insertion step and H2 dissociation step.