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.