Fabrication of Lithium Silicates As Highly Efficient High-Temperature CO2 Sorbents from SBA-15 Precursor

Abstract

A series of lithium silicates with improved CO₂ sorption capacity were successfully synthesized using SBA-15 as the silicon precursor. The influence of Li/Si ratio, calcination temperature, and calcination duration on the chemical composition and CO₂ capture capacity of obtained lithium silicates was systematically investigated. The correlation between CO₂ sorption performance and crystalline phase abundance was determined using X-ray diffraction and a normalized reference intensity ratio method. Under the optimized condition, Li-SBA15-4 prepared using Li/Si = 4 that contains mainly Li₄SiO₄ achieved an extremely high CO₂ capture capacity of 36.3 wt % (corresponding to 99% of the theoretical value of 36.7 wt % for Li₄SiO₄), which is much higher than the Li₄SiO₄ synthesized from conventional SiO₂ sources. It also showed very high cycling stability with only 1.0 wt % capacity loss after 15 cycles. Li-SBA15-10 (Li/Si = 10) that mainly contains Li₈SiO₆ displayed an extremely high CO₂ uptake of 62.0 wt %, but its regeneration capacity was poor, with only 10.5 wt % of reversible CO₂ capture capacity. The influence of CO₂ concentration on the CO₂ capture performance of Li-SBA15-4 and Li-SBA15-10 samples was also studied. With the decrease in CO₂ concentration, relatively lower temperatures are needed for its maximum CO₂ capture capacity. The CO₂ sorption kinetics and mechanism for Li-SBA15-4 and Li-SBA15-10 samples were explored. Overall, we have shown that the lithium silicates synthesized from SBA-15 possessed much improved CO₂ sorption performance than that attained from conventional SiO₂.