The effect of ageing step elimination on the memory effect presented by Mg0.75Al0.25 hydrotalcites (HT) and their catalytic activity for cyanoethylation reaction

The absence of ageing step in the coprecipitation method leads to modification of textural and structural properties of Mg0.75Al0.25 hydrotalcites which are reflected in the “memory effect” and in the catalytic activity of these samples for cyanoethylation reaction between ethanol and acrylonitrile where the beta-ethoxypropionitrile is the prevailing reaction product. The solids were characterised by XRD, DRIFT, TEM and base sites determination by adsorption of molecules with different pKa aiming to establish a correlation between structural characteristics and the catalytic activity.

Graphical AbstractThe absence of the ageing step during the preparation of the hydrotalcite-type solids does not lead to the obtaining of other kind of materials even when working under different atmospheres. Only for the recalcined sample under air atmosphere the presence of MgAl2O4 impurity phase is noticed.a1 — Mg0.75Al0.25 hydrotalcite; a2 — mixed oxide obtained from a1; a3 — reconstructed hydrotalcite from a2; a4 — calcination product of a3; c% — conversion of acrylonitrile after 5 h reaction time; b — weak and medium strength base sites (mmol/g catalyst).Figure optionsDownload as PowerPoint slideResearch highlights
► The absence of the aging step during the preparation of the hydrotalcite-type does not lead to other kind of materials.
► Only for recalcined sample under air atmosphere the presence of MgAl2O4 impurity phase is noticed.
► Following the hydration of the mixed oxides the hydrotalcite-type structures are restored and the catalytic activities of these solids are higher compared to the parent hydrotalcites due to the partial replacement of the carbonate anions by hydroxyl anions which have stronger base character.