Mesoporous smectites incorporated with alkali metal cations as solid base catalysts

Abstract

A series of magnesium containing mesoporous smectites incorporated with alkali hydroxide (NaOH, KOH or LiOH) has been prepared and employed for such base-catalyzed model reactions as transesterification of ethyl acetate with methanol, Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate and one-pot synthesis of dimethyl carbonate (DMC) from propylene oxide, carbon dioxide and methanol. The effects of the quantity and kind of the incorporated alkali atoms on the catalytic properties of the smectites were investigated. Characterization of the smectites has shown that the incorporation of alkali atoms reduces their surface area and total pore volume but enhances the amount and strength of their basic sites. The product yield of the transesterification was increased with the content of alkali atoms incorporated. It has been suggested that the moderately basic sites are responsible for this reaction. The yield of the Knoevenagel reaction depends little on the alkali atom content. Increasing the content of alkali atoms causes the increase in the DMC yield of the one-pot synthesis and the decrease in the yield of methanolysis of propylene oxide, which is the side reaction of the one-pot synthesis. The incorporation of Li was less effective than Na and K for the one-pot reaction. The structures of basic sites over the alkali-incorporated smectites have been discussed.