The impact of the “memory effect” on the catalytic activity of Mg/Al; Mg,Zn/Al; Mg/Al,Ga hydrotalcite-like compounds used as catalysts for cycloxene epoxidation

The epoxidation of cyclohexene by hydrogene peroxide and benzonitrile, in methanol as solvent on solid base catalysts, hydrotalcites (HT) and corresponding mixed oxides (C-HT) was investigated. The employed catalysts were as-synthesized Mg/Al; Mg,Zn/Al; Mg/Ga,Al hydrotalcites, their derived mixed oxides and the corresponding reconstructed hydrotalcite forms (R-HT) obtained via the “memory effect” upon a rehydration treatment of C-HT. The catalysts were characterized by XRD, CO2-TPD and N2 adsorption–desorption measurements.The reconstructed HT samples exhibit higher activity in comparison to the as-synthesized carbonated HT samples. A tentative correlation of the catalytic properties with the base strength of the active sites, the structural and textural characteristics of the catalysts, has been explored.

Zn and Ga containing hydrotalcites present higher activity than the MgAl hydrotalcite for the oxidation of cyclohexene to cyclohexene oxide in the initial stages of the process. This effect is more pronounced for the activity of the derived mixed oxides. The reconstructed hydrotalcite structures obtained by rehydration have higher activity than the as-synthesized HT.Figure optionsDownload as PowerPoint slide