Precise Modulation of Zeolite Acidity by Alkali Metal Ions for Enhancing Catalytic Performance in CO2 Cycloaddition Reactions

The CO₂ cycloaddition route is an effective way to achieve efficient conversion and utilization of CO₂. Zeolites with diverse topologies and tunable acidic sites can efficiently promote the cycloaddition reaction of CO₂ with epoxides. The exchangeable cations in zeolites have a great influence on the performance of the CO₂ cycloaddition, but there are few studies on it. In this paper, the effects of different alkali metal cation (Li⁺, Na⁺, and K⁺)-exchanged zeolites on the cycloaddition reaction of CO₂ were studied to reveal the function of alkali metal cations. The promotion effect of different alkali metal ions on the catalytic performance of the CO₂ cycloaddition reaction gradually increases in the sequence of K⁺ < Na⁺ < Li⁺. Based on the optimized reaction conditions and zeolite topologies, Li-MTW zeolite could achieve up to 95.99% yield of styrene carbonate, which could still be maintained at as high as 91.67% after five catalytic cycles. The computational results revealed that the ring-opening of styrene oxide is the rate-determining step of the catalytic cycle and Li-MTW has a lower reaction activation energy. This work will further deepen our understanding of the effect of alkali metal ions in zeolite on CO₂ cycloaddition reactions.