Structural Modulation of ZSM-5 Derived Li4SiO4 Sorbents for Enhanced High-Temperature CO2 Capture

The utilization of high-temperature lithium-based sorbents is one of the important pathways to achieve carbon dioxide capture but suffers from its low CO₂ uptake kinetics. In this study, ZSM-5 zeolite is used as the silicon source and a precursor skeleton to synthesize molecular sieve-derived Li₄SiO₄-based CO₂ sorbents, namely, ZSM-5-LS2, -LS3, and -LS4, corresponding to their lithium-to-silicon mole ratios of 2:1, 3:1, and 4:1. The adsorption capacities of ZSM-5-LS2, -LS3, and -LS4 are 0.12, 0.26, and 0.32 g of CO₂/g of Li₄SiO₄, respectively. ZSM-5-LS4 shows the highest CO₂ adsorption capacity while presenting poor cyclic stability. The adsorption capacity of ZSM-5-LS4 decreases to 83.3% of the original performance at the 30th cycle, while the performance of ZSM-5-LS2, -LS3 remains essentially unchanged after 30 cycles, demonstrating the significance of ZSM-5 derived Li₄SiO₄ under a moderate lithium-to-silicon mole ratio. In situ diffuse reflectance Fourier transform infrared spectroscopy and operando X-ray diffraction tests verify the generation of Li₂CO₃ and Li₂SiO₃ after CO₂ adsorption and the regeneration of Li₄SiO₄ after desorption. This study provides an important experimental basis for the exploitation of molecular sieve-derived lithium-based high-performance CO₂ sorbents.