Reconstruction of copper nanoparticles catalysts and its catalytic performance for synthesis of dimethyl carbonate

Dimethyl carbonate (DMC) is an important and environmentally friendly chemical intermediate to meet the growing demand for a clean and sustainable energy supply. Among several routes for DMC synthesis, the oxidative carbonylation of methanol has attracted much attention with the advantages of a high utilization rate of carbon source, moderate operating conditions and environmental benefits. More importantly, the oxidative carbonylation of methanol is an important development route of modern coal chemical industry in China, and the key lies in the design of highly efficient catalysts. Copper-based catalysts have been used extensively in this reaction. Problems, such as reactor corrosion and catalyst deactivation, occur with chlorine-containing catalysts. The development of chlorine-free catalysts is the focus of current research. Recently, Cu-based catalysts supported on carbon materials have been used extensively in DMC synthesis because of its high activity, high selectivity and facile preparation process. However, the carbon-supported Cu catalysts suffer from the leaching and aggregation of Cu nanoparticles (NPs) in the harsh reaction conditions of high temperature, high pressure as well as severe stirring, leading to the deactivation. It has become a key scienctific problem that needs to be addressed urgently. In our previous studies, several strategies have been attempted to solve the deactivation problem caused by these reasons. For instance, encapsulating Cu NPs with hollow porous carbon spheres or mesoporous carbon materials. Besides, the introduction of N species in the carbon framework or sulfonic acid groups and oxygen-containing groups on the surface of carbon materials leads to an anchoring effect on Cu NPs. Great progress has been made via these methods, yet still unsatisfactory. Supported metal clusters have adjacent metal sites, countable numbers of atoms in each clusters, and limited size range (normally smaller than 2 nm). Benefiting from these distinct geometric and electronic structures, supported metal clusters can trigger synergistic effects among every metal atom, and thus exhibiting enhanced catalytic activity and selectivity in catalysis. Besides, the strong metal-support interaction on supported metal clusters improve the stability of metal clusters, enhancing the catalytic stability. To prevent the aggregation of metal clusters, the metal loading of supported metal clusters catalysts are generally kept at a low level (≤1%). However, catalysts with insufficient numbers of active sites always lead to compromised mass-activity, which greatly restrict them from industrial applications. Hence, the synthesis of supported metal clusters with high metal loading and high stability is a great challenge. In this study, the Cu clusters catalysts with high Cu loading were synthesized via liquid phase reconstruction method under the condition of water and CO. The optimal 15Cu/NCNS-12-CO exhibited superb activity with STY_DMC of 3520 mg/(g·h) and stability with the loss rate of 28% after 10 cycles. A series of characterization showed that the strongly reducing CO not only resulted in the partial reconstruction of copper nanoparticles (from ~9.7 nm to ~1.34 nm), but also effectively maintained the existence of Cu⁰ species, improving the catalytic activity and stability. Further investigation showed that the reconstruction of Cu nanoparticles was dependent on the interaction of atmosphere-metal-support, and was reversible under the oxidation and reducing atmosphere.