Highly basic catalysts obtained by intercalation of La-containing anionic complexes in layered double hydroxides

Nanocomposites have been obtained by intercalation of preformed negatively charged guest La hydroxy citrate colloids into host Mg/Al layered double hydroxides (LDH). These compounds have been used as precursors for La/Mg(Al)O mixed oxides catalysts. The La loading has been controlled by the colloids exchange rate in order to achieve a better dispersion of the lanthanum cations and thus improve the basic properties of the new catalysts. The increase of the d0 0 3 interlayer distance from 0.830 nm in the host LDH to 1.196 nm in the nanocomposites shows that the intercalation has taken place leading to 1.82–11.16 wt% of lanthanum cation loadings. The basic properties of the La/Mg(Al)O(x) mixed oxides were evaluated qualitatively using Hammett indicators and quantitatively by TPD of CO2. Both techniques indicated the presence of strong basic sites. The transesterification of 1-phenylethanol with diethylcarbonate (DEC), which is known to involve strong basic sites, was used to evaluate the catalytic activity of the La/Mg(Al)O(x) mixed oxides. Yields into carbonate product increase with the density of strong basic sites of the catalyst.

Preformed negatively charged guest La hydroxy citrate colloids were introduced into host Mg/Al LDHs to give nanocomposites precursors for La/Mg(Al)O(x) mixed oxides. The TPD of CO2 indicates the generation of strong basic sites. Accordingly the La/Mg(Al)O(x) mixed oxides were found highly active for the synthesis of unsymmetrical organic carbonates.Figure optionsDownload high-quality image (19 K)Download as PowerPoint slide