Glycerol Esterification over Sn(II)-Exchanged Keggin Heteropoly Salt Catalysts: Effect of Thermal Treatment Temperature

Abstract

In this work, Sn(II)-exchanged Keggin heteropoly acid salts were evaluated as solid catalysts in glycerol esterification reactions with acetic acid. All the Sn(II) heteropoly salts and their precursor Keggin acids were characterized by FT-IR/ATR, XRD, TG/DSC, BET, and EDS/SEM analyses. Among salts synthesized (i.e., Sn3/2PW12O40, Sn2SiW12O40, and Sn3/2PMo12O40), Sn3/2PW12O40 was the most active and selective catalyst toward glycerol esters. Effects of thermal treatment on the physical and chemical properties of Sn3/2PW12O40 were investigated. The Sn3/2PW12O40-300 K catalyst was efficiently recovered and reused without a loss in activity. The influences of main reaction parameters such as reaction temperature, the stoichiometry of reactants, load, and thermal treatment temperature of the Sn3/2PW12O40 catalyst were assessed. The simple workup of synthesis and the high activity and selectivity for glycerol esters in addition to the high efficiency during successive recycles are positive aspects of this catalyst.