Abstract: Among the many strategies for CO₂ resource utilization, the synthetic technology of cyclic carbonates with 100 % atom economy through CO₂and epoxide is one of the most industrially viable routes, but its efficiency has been severely hampered by the lack of highly active catalytic sites. Moreover, due to the intrinsic thermodynamic stability and kinetic inertia of CO₂ and the higher energy barrier of the ring-opening reaction of epoxides, the heterogeneous catalytic conversion of CO₂ highly depends on harsh operating conditions, high temperatures and pressures, and the incorporation of cocatalysts. The development of efficient heterogeneous catalysts for CO₂ conversion under cocatalyst-free and mild conditions has always been a challenge. Herein, we have proposed a synergetic strategy of facet and vacancy engineering for the construction of highly efficient heterogeneous catalyst BiO_1-xBr_1-y-(010) for CO₂ cycloaddition, where introducing the OVs-BrVs pairs into typical (010) facets BiOBr with simultaneous surface Lewis acid sites Bi³⁺ and nucleophilic sites Br^-. By combining theoretical calculations and a series of systematic experiments, such as CO₂ temperature-programmed desorption, electron paramagnetic resonance and fluorescence probe analysis experiments, the introduced OVs-BrVs pair can not only form Bi³⁺-Bi^(3-x)+ dual active sites on the surface, which activate PO and CO₂ respectively to reduce the energy barrier of CO₂ insertion, but also activate Br^- near BrVs to enhance their nucleophilic attacking ability and reduce the energy barrier of epoxides ring-opening. As a result, the BiO_1-xBr_1-y-(010) with abundant surface OVs-BrVs pairs showed a high cyclic carbonates conversion of 99 % with 100 % selectivity under cocatalyst-free and mild conditions, far surpassing most heterogeneous catalytic systems. This work provides a completely new strategy to construct high-performance heterogeneous CO₂ cycloaddition catalysts through a simple facet and vacancy engineering strategy to overcome the harsh operating conditions limitation and the use of cocatalysts.

Key words: CO₂ cycloaddition reaction, Vacancy engineering, Facet engineering, Heterogeneous catalysis