Preparation Of Yolk-Shell Cu@C Confined Nanoreactors And Its Application For Dimethyl Carbonate Synthesis

Dimethyl carbonate (DMC), as an important green downstream product of methanol, is now becoming a focus of research in coal chemical industry of China. Activated carbon supported Cu catalysts (Cu/AC) show excellent performance in the oxidative carbonylation of methanol to DMC, however, owing to its extremely high surface energy, copper nanoparticles tend to easily aggregate in reaction, accompanied by a corresponding loss of catalytic activity, which significantly limits its practical applications for DMC synthesis. In this work, we have presented a facile synthetic method for the fabrication of a yolk-shell nanocomposite with tunable Cu cores encapsulated within hollow carbon spheres (Cu@C) by employing the ship-in-bottle synthetic strategy. The preparation mechanism of Cu@C was deeply discussed assisted with various characterizations. It is expected that the confined nanostructures of Cu@C could protect the Cu nanoparticles from aggregation and act as a ideal nanoreactors for oxidative carbonylation of methanol. The size of the Cu nanoparticles could be easily tuned from 30 to 55 nm with narrow particle-size distributions by adjusting the concentration of copper nitrate solution used in the synthesis procedure. Furthermore, with the addition of alkali in copper salts, multiple Cu cores can be generated. In addition, the carbon shell can effectively prevent the Cu particles migration and aggregation under high-temperature condition. More importantly, the synthesis route described opens the door for the preparation of a wide variety of yolk-shell nanomaterials with complex metal core structures encapsulated by hollow carbon shell that could be difficult to obtain using standard synthetic techniques.The shell porosity structure of Cu@C has significant influence on the catalytic performance for oxidative carbonaylation of methanol. The Cu@C catalysts showed low catalytic activity for the limitation of diffusion rate by reactant and product moleculars through the carbon shell. After activation with KOH at high temperature, the catalysts are given rise to a porous carbon structure with a high specific surface area and pore volumes. Meanwhile, more Cu cores with smaller sizes were formed inside or in the carbon shell, which provided more active sites. The actived Cu@C catalysts exhibited excellent results as compared to those unactivated catalysts, due to fast diffusion of molecules between the outer shell and the active phase of Cu core.