Facile preparation of nickel-poor layered double hydroxides from mechanochemically pretreated gibbsite with a variety of interlamellar anions and their use as catalyst precursors for CO₂ hydrogenation

A simple synthetic route of preparing NiAl4-layered double hydroxides (LDHs) was developed. First, Al(OH)3 was pretreated by using high-energy dry-milling. This was followed by impregnation with moderately concentrated aqueous Ni-salt solutions with different counter anions under mild conditions. Using this protocol, beside the already known NiAl4-LDHs with chloride, nitrate, sulfate interlamellar anions, bromide, iodide, perchlorate and sulfamate ion intercalated versions were also possible to be prepared for the first time. Catalysts obtained from these LDHs proved to be active in CO2 hydrogenation reaction. The quality of interlayer anions was found to exert a profound effect on the topotactic transformation of LDHs, the in situ reduction of nickel and the formation of spinel-type oxides. Catalysts from sulfate and sulfamate containing NiAl4-LDHs possessed outstandingly high (>90 %) CO selectivity independently from the reaction temperatures, while those obtained from nitrate and perchlorate containing LDHs facilitated mostly and robustly the formation of methane.