Promotion effect of coexistent hydromagnesite in a highly active solid base hydrotalcite catalyst for transesterifications of glycols into cyclic carbonates

Mg-Al hydrotalcites (HTs) prepared with a co-precipitation method in the different conditions were examined for the selective synthesis of carbonates via transesterification of glycols including glycerol, propylene glycol and ethylene glycol. The prepared HT aged for 18 h exhibited a significant catalytic activity over the reaction. XRD and nitrogen adsorption measurements indicate the formation of the hydromagnesite (HM) possessing a high surface area after aging, however, the HM itself is inactive for the reaction. Additionally, progress of the reaction suggests the HT involving HM (HT-HM) shows a gradual increase of glycerol carbonate yield following large uptake of glycerol. The catalyst exhibited a significant catalytic activity in the reaction under the low concentration of glycerol. Therefore, we concluded that the HT-HM acts as a highly active solid base catalyst for the selective synthesis of carbonates via transesterification since the coexistent HM increased the catalytic activity by increasing both surface area and adsorption sites for substrate during the reaction.