Na-doped Li4SiO4 as an efficient sorbent for low-concentration CO2 capture at high temperature: Superior adsorption and rapid kinetics mechanism

Lithium silicate (Li 4 SiO 4 ) sorbent has garnered attention in CO 2 capture due to its high theoretical adsorption capacity and fast kinetics. However, its adsorption capacity and kinetics were hindered by low CO 2 concentration. Improving adsorption performance of Li 4 SiO 4 at low CO 2 concentration has become the key to industrial application. In this work, high-activity Na-doped Li 4 SiO 4 with controllable active substance Li 3 NaSiO 4 was achieved. The influences of raw materials ratios on the CO 2 adsorption performance were systematically investigated. When R Li/Si =4.05:1 and R Na/Si =0.15:1, the sample exhibited the highest adsorption capacity of 32.28 wt% with an equilibrium time of 29 min, and a superior stable capacity of 31.09 wt% in 15 cycles. Importantly, the double exponential fitting revealed that LiNaCO 3 accelerated the ion diffusion rate and real-time adsorption processes showed Li 3 NaSiO 4 expedited surface chemical reaction rate. Based on these, a novel Na 2 CO 3 eutectic doping mechanism was proposed. The active substance Li 3 NaSiO 4 , generated through Na doping, along with its product formed from the reaction with CO 2 , molten LiNaCO 3 , acted synergistically to improve adsorption performance by accelerating surface chemical reaction rate and ion diffusion rate. Compared with other doped Li 4 SiO 4 , the sorbent prepared in this work demonstrated competitive adsorption performance, providing theoretical and technical support for the large-scale production of high-activity Li 4 SiO 4 .