Immobilization of triazabicyclodecene in surfactant modified Mg/Al layered double hydroxides

Abstract

In recent years, layered double hydroxides (LDHs) have received much interest as host materials for the construction of organic–inorganic supramolecular structures by an anion exchange method. This study demonstrates the preparation of a series of solid base catalysts through attachment of triazabicyclodecene (TBD) to Mg/Al-LDH surfaces with different Mg/Al molar ratios (Mg/Al = 3, 4 and 5). A new three-stage approach was taken to obtain TBD-LDH materials: (i) an anionic surfactant, sodium dodecyl sulfate (SDS) was intercalated in parent LDH replacing nitrates from interlayer via anion exchange to widen the gallery of LDH, (ii) a silane coupling agent (3-glycidyloxypropyl) trimethoxysilane (3GPS) was used to attach TBD with the terminal glycidyl groups, and (iii) interlayer molecules from SDS-LDH gallery were replaced by the 3GPS moieties containing TBD. The surfactant modified Mg/Al LDH materials showed an increase in interlayer distance (maximum 44.8 Å) as compared to unmodified Mg/Al LDH (8.8 Å). Infrared and Raman spectroscopy results were in agreement with the proposed organic functionalized structure. Therefore, based on these observations, a schematic representation of the TBD functionalized LDH surface is also presented. The temperature programmed desorption (TPD) study on the different products showed approximately 3–5 times higher basic properties than those of pristine LDHs. Thermal decomposition was changed significantly after organic modification of LDHs. All TBD-LDHs are found to be effective catalysts for the transesterification of canola oil with dimethyl carbonate (DMC) for biofuel production under mild conditions (atmospheric pressure and 70 °C).