Facile synthesis of macroporous Li4SiO4 with remarkably enhanced CO2 adsorption kinetics

Abstract

Lithium orthosilicate (Li4SiO4) has attracted extensive scientific attention due to its large CO2 adsorption capacity at high temperature (650–700°C) and low material cost. However, the conventional nonporous Li4SiO4 ceramic shows very poor CO2 adsorption performance below 600°C, which is a relevant condition for possible applications such as sorption-enhanced steam methane reforming. In the present work, in order to increase the CO2 adsorption kinetics below 600°C, Li4SiO4 was synthesized in the form of a macroporous structure by a simple solid-state transformation method using LiOH and fumed silica as a precursor for Li and SiO2, respectively. The use of LiOH substantially decreased the synthesis temperature of Li4SiO4 down to 600°C, compared with the conventional syntheses using other lithium precursors such as Li2CO3 and LiNO3 that require very high synthesis temperature (>700°C). The decrease of the material synthesis temperature circumvents undesirable sintering of initially formed small Li4SiO4 crystallites and leads to the formation of a highly macroporous (macropore volume >0.6mLg−1) Li4SiO4 framework that has a significantly higher BET surface area (15m2g−1) than conventional nonporous Li4SiO4 (<1.0m2g−1). The macroporous Li4SiO4 exhibited dramatically enhanced CO2 adsorption capacity (29.8wt%) and rate (56.1mgg−1min−1), compared with the CO2 adsorption capacities (1.40–7.79wt%) and rates (0.420–2.95mgg−1min−1) of nonporous Li4SiO4 materials. Adsorption–desorption cycles at 550°C could be repeated 10 times without a significant decrease in the adsorption capacity or the rate capability.