Acetate intercalated Mg-Al layered double hydroxides (LDHs) through modified amide hydrolysis: a new route to synthesize novel mixed metal oxides (MMOs) for CO2capture

Abstract

Layered double hydroxide (LDH) based mixed metal oxides (MMOs) are promising high temperature CO2capture sorbents. In order to improve their CO2capture 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 CO2capture 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) m2g−1, compared to MMOs derived from anion exchanged Mg-Al-acetate LDH (118 m2g−1). The MMOs synthesized by acetamide hydrolysis captured 1.2 mmol g−1and 0. 87 mmol g−1of CO2at 200 and 300 °C (atmospheric pressure), respectively. The CO2capture capacity realized was increased more than twofold compared to the CO2capture capacity of MMOs derived from anion exchanged acetate LDH (0.57 mmol g−1) tested under similar conditions. The developed MMOs showed promising CO2capture (1.0 mmol g−1) capacity at industrially relevant CO2concentration (14%).