A one-pot synthesis of hybrid organo-layered double hydroxidecatalyst precursors

Abstract

Organo-layered double hydroxides (LDHs) have attracted much attention recently for their utility as solid base catalysts, providing an environmentally friendly heterogeneous phase alternative to conventional stoichiometric liquid bases. Here we describe a synthetic approach for the production of layered double hydroxides containing organic (acetate) anions by a method that requires no excess of base, filtering or washing of the product. A mixture of a slurry of aluminium trihydroxide (or its thermally treated form), magnesium oxide, and magnesium acetate are reacted under atmospheric or autogenous conditions to prepare MgAl-acetate LDHs of general formula Mg_1−xAl_x(OH)₂(CH₃CO₂)_x·yH₂O. Using this synthetic procedure it has been found that MgAl-acetate LDHs with either a full or partial acetate loading may be prepared for a range of Mg/Al stoichiometries. The LDHs formed have been characterised by X-ray diffraction, infra-red spectroscopy, solid state nmr and thermal methods. Depending on the synthesis method, the acetate LDHs had an interlayer spacing of between ca. 8.4 and 14.8 Å indicating the formation of monolayers and bilayers of acetate anions, respectively, in the LDH host.