Acetate intercalated Mg-Al layered double hydroxides (LDHs) through modified amide hydrolysis: a new route to synthesize novel mixed metal oxides (MMOs) for CO capture.

Layered double hydroxide (LDH) based mixed metal oxides (MMOs) are promising high temperature CO2 capture sorbents. In order to improve their CO2 capture capacity, it is crucial to bring in changes to their physicochemical properties such as morphology, particle size, surface area and activity by tuning the synthesis method. Here we report a modified amide hydrolysis method to synthesize LDHs with a mixed morphology and better CO2 capture properties. Acetate intercalated Mg-Al LDHs with two different Mg/Al ratios (3 and 4) were synthesized by employing metal hydroxides as the starting precursors and acetamide as the hydrolysing agent. The resultant LDHs crystallized in a new morphology having a combination of both fibrous and sheet like crystallites. The MMOs derived from Mg-Al-acetate LDHs retained the mixed morphology observed in the precursor LDHs. The resultant MMOs showed almost a threefold increase in the BET surface area, 316 (Mg/Al = 3) and 341 (Mg/Al = 4) m2 g-1, compared to MMOs derived from anion exchanged Mg-Al-acetate LDH (118 m2 g-1). The MMOs synthesized by acetamide hydrolysis captured 1.2 mmol g-1 and 0. 87 mmol g-1 of CO2 at 200 and 300 °C (atmospheric pressure), respectively. The CO2 capture capacity realized was increased more than twofold compared to the CO2 capture capacity of MMOs derived from anion exchanged acetate LDH (0.57 mmol g-1) tested under similar conditions. The developed MMOs showed promising CO2 capture (1.0 mmol g-1) capacity at industrially relevant CO2 concentration (14%).