Br--intercalated ZnMgAl-LDH Heterogeneous Catalyst for Efficient Cycloaddition of CO2 with Propylene Oxide

Introduction The catalytic cycloaddition of CO2 with epoxides to produce cyclic carbonates represents one of the most promising CO2 utilization technologies, offering 100% atomic economy under mild conditions. Nevertheless, the development of cost-effective heterogeneous catalysts with high performance under solvent- and cocatalyst-free conditions remains a grand challenge. Herein, we report the rational design and synthesis of a multifunctional heterogeneous catalyst for efficient CO2/propylene oxide (PO) cycloaddition under solvent- and cocatalyst-free conditions. Methods The ZnMgAl-Br- heterogeneous catalyst was prepared through an integrated coprecipitation-ion exchange method. Structural and physicochemical properties were systematically characterized using SEM, XRD, EDX mapping, BET, and NH3-TPD, which confirmed the coexistence of abundant Br- nucleophiles and –OH hydrogen-bond donors within the layered matrix. Catalytic tests were conducted in a 50 mL stainless steel autoclave. Results A Br- intercalated ZnMgAl layered double hydroxide (ZnMgAl-Br-) catalyst was successfully constructed, integrating nucleophilic Br- anions with hydrogen-bond donating –OH groups in a precisely engineered layered framework. Under optimized conditions (140oC, 7 h, 2.5 MPa), the catalyst achieved 99.2% PO conversion, 98.7% PC selectivity, and 97.9% PC yield. The result represents a remarkable improvement compared with benchmark catalysts (MgAl-Br−: 50.5% yield; ZnMgAl-NO3−: 13.1% yield), highlighting the critical synergy among Br- nucleophiles, Zn species, and –OH groups. Discussion The results demonstrate that the cooperative interaction between Br- and –OH groups is central to the catalytic efficiency of CO2/PO cycloaddition. Incorporation of Zn species expanded the interlayer spacing and optimized the spatial arrangement of Br−/-OH sites, thereby enhancing cooperative catalysis. Conclusion The findings highlight the critical role of Br- nucleophiles and the Zn-modified layered structures in enabling cooperative catalysis. This work establishes a rational strategy for designing multifunctional heterogeneous catalysts for efficient CO2 utilization through epoxide cycloaddition.