Acetate intercalated Mg-Al layered double hydroxides (LDHs) through modified amide hydrolysis: A new route to synthesize novel mixed metal oxides (MMOs) for CO₂ 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%).