Synthesis of glycerol carbonate by direct carbonylation of glycerol with CO2 over solid catalysts derived from Zn/Al/La and Zn/Al/La/M (M = Li, Mg and Zr) hydrotalcites

Abstract

Zn/Al/La and Zn/Al/La/M (M = Li, Mg, Zr) mixed oxides were obtained by calcination of hydrotalcite precursors and tested for glycerol carbonate (GC) synthesis from CO₂ carbonylation. The results indicated the catalytic activity may be associated with the large specific surface area, the high surface content of Zn and the high binding energy of Zn atoms as well as the high density of moderately basic sites. The good result was obtained on the catalyst with a molar ratio of Zn : La : Al = 4 : 1 : 1 and, within a certain range, glycerol conversion and GC yield increase linearly upon the increase of the density of moderately basic sites. In addition, the catalytic activity was obviously improved upon introduction of Li, Mg and Zr. The effect of reaction parameters on the carbonylation of glycerol was also studied. The DRIFTS results suggest that the activated CO₂ may be in the form of a bridged bidentate carbonate that inserts into zinc glycerolate to form an intermediate species of a seven-membered ring ester followed by intramolecular rearrangement to produce GC. Theoretical calculation results indicated that the seven-membered ring ester has good stability and the formation process happens spontaneously.