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

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.