Kinetic and Reaction Mechanism of CO₂ Sorption on Li₄SiO₄:  Study of the Particle Size Effect

Lithium orthosilicate (Li 4 SiO 4 ) was synthesized by three different techniques: the solid-state reaction, precipitation, and sol−gel (using a microwave oven) methods. The better results were obtained by the two first methods. In the third case, pure Li 4 SiO 4 could not be obtained, because the microwaves produced the lithium sublimation. The samples were characterized by X-ray diffraction, scanning electron microscopy, N 2 adsorption, and thermogravimetric analysis under a flux of CO 2 . Different particles sizes were obtained as a function of the method of synthesis, and the CO 2 sorption analyses gave different results. The particle size modified the stability of the Li 4 SiO 4 during the CO 2 sorption/desorption cycles, due to lithium sublimation, as Li 2 O. Conversely, the isothermal study allowed measuring the kinetic parameters for the chemisorption and diffusion processes, as a function of the particle size. As could be expected, the activation energies obtained, for the small particles, were smaller than those obtained for the large particles. These results were explained in terms of reactivity, for the chemisorption process, and in terms of geometry, for the diffusion process.