Catalytic performance of kenyaite and magadiite lamellar silicates for the production of α,β-unsaturated esters

• Co3+, Al3+, Er3+-containing kenyaite or magadiite were synthesized.
• The catalyst loading, type of solvent and temperature were investigated.
• Knoevenagel condensation performance was due to the trivalent cations.
• The affinity between Si and Er in kenyaite structure explained ErKen performance.

Trivalent cation (Co3+, Al3+, Er3+) containing-kenyaite and magadiite lamellar silicates were synthesized and tested as catalysts for the Knoevenagel condensation of butyraldehyde (BUT) with ethyl cyanoacetate (CAE). The as-synthesized catalysts were thoroughly characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, solid state nuclear magnetic resonance of silicon (29Si NMR) and nitrogen physisorption measurements. Significant effects of the structural and textural features of kenyaite and magadiite on catalyst activity in the Knoevenagel condensation were observed. The high catalytic activity and selectivity were ascribed to the cations incorporated into silicate layers, being Co3+ and Al3+ leached from their structures during the reaction. Er3+-containing kenyaite exhibited excellent catalytic activity in the Knoevenagel condensation, suggesting that the presence of silanol groups along with trivalent cation was responsible for the exceptional activity of the catalyst at mild conditions. The effects of catalyst loading, type of solvent and temperature on the catalytic properties demonstrated that a 100 mg of catalyst mass and BUT/CAE molar ratio of 1 in the presence of toluene at 90 °C were the best conditions for testing Er3+-containing kenyaite and magadiite catalysts. The affinity between Si and Er took place in kenyaite structure and this could explain the better performance of Er3+-containing kenyaite, since Er remained in the framework during the reaction. On the contrary, leaching of the erbium in magadiite was responsible for the lesser performance of the solid.