The activity of yttrium-modified Mg,Al hydrotalcites in the epoxidation of styrene with hydrogen peroxide

Modification of Mg,Al hydrotalcite with Y3+ prepared following co-precipitation at low suprasaturation led to an improvement of the activity and selectivity for styrene epoxidation with hydrogen peroxide in acetonitrile. The materials were characterized using several techniques such as XRD, DRIFT, TEM, CO2-TPD and adsorption–desorption isotherms of nitrogen at −196 °C. It was thus demonstrated that the memory effect of hydrotalcite acts very quickly even in an unfriendly environment like that generated by hydrogen peroxide. A direct correlation between the memory effect and the catalytic behavior in the epoxidation of the styrene has been demonstrated. MgO and Al2O3 were also prepared using the precipitation method. The investigation of MgO, Al2O3 and of a mechanic mixture of them showed that the activity of the catalysts in this reaction correlates very well with their basicity.

Figure optionsDownload high-quality image (94 K)Download as PowerPoint slideHighlights
► The introduction of yttrium in Mg,Al hydrotalcite occurs without its insertion in the Mg or Al octahedral positions.
► The lower electronegativity of yttrium led to an increase of the basicity.
► The memory effect plays an important role in the reconstruction of the LDH structure from the beginning of the reaction.
► Hydration of mixed oxides generates a worm texture and contributes to the decrease of the surface area.
► During reconstruction of the LDH under inert atmosphere part of carbonic anions are replaced by hydroxyl groups.