Double-shell microcapsules with spatially arranged Au nanoparticles and single Zn atoms for tandem synthesis of cyclic carbonates

Abstract

Tandem catalysts with multifunctional sites can achieve high-efficiency catalytic transformations for quickly converting simple raw materials into complex value-added products. The integration of highly active species of metal nanoparticles (NPs) and single-atom catalytic sites (SACs) into one tandem system promises to synthesize an ideal bifunctional catalyst on account of the synergistic effect between NPs and SACs. However, such ideas face some challenges as deactivation or loss of active species, and low efficiency or side reactions caused by the disorder of different active species. Herein, a double-shell microencapsulated nanoreactor was fabricated as a bifunctional catalyst for the one-pot synthesis of cyclic carbonates from olefins. The microcapsules consist of an inner shell of nitrogen-doped porous carbon rich in Zn SACs, an outer shell of mesoporous SiO₂, and Au NPs confined between the outer and inner shells, noted as Zn–N–C/Au@mSiO₂. Particularly, two active species are spatially compartmented within microcapsules. Furthermore, the catalyst was applied in the one-pot synthesis of styrene carbonate from styrene with CO₂ under normal pressure and showed admirable performance. The yield of cyclic carbonate reached 92.9% at 93.2% olefins conversion. Furthermore, the catalyst shows good reusability with little loss of catalytic performance (4.0%) even after using it 15 consecutive times. The unique structure used in this work can rationally integrate diverse catalytic species into one system and offering adequate protection, which provides an effective strategy for the development of multi-site catalysts.