Molten shell-activated, high-performance, un-doped Li4SiO4 for high-temperature CO2 capture at low CO2 concentrations

Lithium orthosilicate (Li 4 SiO 4 ) represents a potential class of high-temperature sorbents for CO 2 capture in power plants and sorption enhanced methane reforming to produce H 2 . However, conventional wisdom suggests that pure Li 4 SiO 4 should have extremely slow sorption kinetics at realistic low CO 2 concentrations. Here, we report the opposite result: using a simple and cost-effective glucose-based mild combustion procedure, an unusually efficient and pure form of Li 4 SiO 4 (MC-0.6) was synthesized to achieve a maximum uptake capacity of 35.0 wt% at 580 °C for CO 2 concentrations under 15 vol% and maintained this capacity over multiple cycles. The characterization results showed that highly porous nano-agglomerate-like (50–100 nm) morphologies were apparent and ensured a rapid surface-sorption of CO 2 . In this process, a macroporous nano-sized Li 2 SiO 3 cover on the melt layer of Li 2 CO 3 was identified for the first time. This special structure appeared to accelerate the transportation of CO 2 and the diffusion of Li + and O 2− through a molten layer enhancing contact with CO 2 . Thus, the sample MC-0.6 reduced both the surface-sorption and diffusion kinetics dependence on low CO 2 concentrations. Rather than use traditional approaches (controlled morphologies combined with doping), we have demonstrated that the slow kinetics can be overcome simply by a controlled morphologies strategy, which opens up a new direction for the synthesis of high-performance Li 4 SiO 4 sorbents.