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.