Key Takeaways & Executive Findings
- •• • The optimized Moac@TS catalyst achieved a styrene conversion of 83.4% and a selectivity of 75.3% under mild conditions, demonstrating effective rate balance between epoxidation and cycloaddition steps. • • Encapsulation of molybdenum acetylacetonate within TS-1 zeolite preserves the intrinsic crystallinity, porosity, and tetrahedral Ti sites, ensuring structural stability and resistance to active species leaching over five repeated cycles. • • Electronic interaction between encapsulated Mo species and framework Ti atoms creates synergistic active centers, which are decisive in regulating the formation and transformation of the styrene oxide intermediate. • • Adjusting Mo loading directly influences the epoxidation rate, allowing fine control over the relative rates of the two reaction steps, which is essential for maximizing carbonate selectivity and minimizing side reactions.
Abstract
The coupling of CO2 with olefins to produce cyclic carbonates has emerged as an important research topic in sustainable chemistry, owing to its high atom economy and the wide applicability of the resulting products. However, this reaction faces a significant challenge due to the mismatch between the rates of the epoxidation and cycloaddition steps. In this work, a series of TS-1 zeolite catalysts encapsulating different amounts of molybdenum acetylacetonate were prepared through hydrothermal synthesis followed by post-treatment, with the aim of elucidating the rate balance between the epoxidation and cycloaddition steps and the underlying regulation mechanism. Characterization results show that the Mo species were present as highly dispersed molybdenum acetylacetonate complexes that were stably confined within the TS-1 framework. These complexes interact electronically with the tetra-coordinated Ti sites to form synergistic active centers, while imposing negligible effects on the zeolite structure and porosity. In the CO2-styrene coupling reaction, tuning the Mo loading enabled effective control over the epoxidation rate, thereby achieving an appropriate balance with the subsequent cycloaddition step. The optimized catalyst delivered excellent performance under mild conditions, with a styrene conversion of 83.4% and a selectivity of 75.3%, and also exhibited outstanding recyclability. Overall, this encapsulated catalyst successfully addresses the dual challenges of rate matching and active-site stability in CO2–olefin coupling, providing valuable insights for the rational design of efficient, durable bifunctional catalysts.
1. Introduction
The direct conversion of olefins and CO2 into cyclic carbonates represents a sustainable alternative to conventional epoxide routes, yet its industrial deployment has been hindered by the intrinsic mismatch between the rates of epoxidation and cycloaddition. Traditional catalysts often fail to balance these sequential steps, leading to low selectivity and poor stability under reaction conditions. The challenge is compounded by the need for active sites that can withstand the harsh conditions of CO2 activation while maintaining high activity.
This work addresses the bottleneck by encapsulating molybdenum acetylacetonate within TS-1 zeolite, creating a bifunctional catalyst that integrates epoxidation and cycloaddition functionalities. The encapsulation strategy not only stabilizes the active Mo species but also promotes electronic synergy with framework Ti sites, enabling precise control over the reaction kinetics. The reported catalyst achieves high conversion and selectivity under mild conditions, offering a robust solution to the rate-matching problem and paving the way for more efficient and durable integrated catalysts.
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XING Mengjiao, TANG Jianyu, ZHAO Yindi, CAI Yushan, LIANG Xingkai, XIE Jinxia, ZHANG Tianfu, FANG Yiwen, LIU Suyao (2026). MoO2(acac)2-encapsulated in TS-1 zeolite catalyst for CO2 coupling with olefins to cyclic carbonates. Journal of Fuel Chemistry and Technology. https://doi.org/10.1016/S1872-5813(25)60628-1
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Frequently Asked Questions
What is the specific role of the tetra-coordinated Ti sites in the TS-1 framework in the synergistic active centers?
The tetra-coordinated Ti sites in TS-1 interact electronically with the encapsulated Mo species, forming synergistic active centers that are crucial for regulating the formation and subsequent transformation of the styrene oxide intermediate. This interaction enhances the catalytic activity and selectivity of the epoxidation–cycloaddition tandem process.
How does the Mo loading affect the balance between epoxidation and cycloaddition rates?
Adjusting the Mo loading directly influences the epoxidation rate. By tuning the Mo content, the relative rates of epoxidation and cycloaddition can be finely controlled, achieving an appropriate balance that maximizes cyclic carbonate selectivity and minimizes side reactions associated with excess styrene oxide accumulation.
What evidence confirms the stability and resistance to leaching of the encapsulated Mo species?
The optimized catalyst exhibited stable and excellent performance over five repeated cycles under mild conditions, confirming the robustness of the encapsulated structure and the resistance of the active species to leaching. Characterization results from XRD, FT-IR, UV-vis, and TEM also confirmed that the Mo species remained highly dispersed and confined within the TS-1 framework.
What are the key advantages of using olefins instead of epoxides as starting materials for cyclic carbonate synthesis?
Olefins are more accessible, less toxic, and cheaper than epoxides, making them attractive and sustainable alternatives. The direct one-pot conversion of olefins and CO2 into cyclic carbonates offers high atom economy and avoids the safety and environmental concerns associated with epoxide handling.
What is the significance of achieving a styrene conversion of 83.4% and a selectivity of 75.3% under mild conditions?
These performance metrics demonstrate that the encapsulated catalyst can effectively mediate the tandem epoxidation–cycloaddition process under mild conditions, achieving high conversion and selectivity. This is significant because it addresses the dual challenges of rate matching and active-site stability, providing a viable route for industrial application.
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