Solid base catalysts derived from Ca-M-Al (M = Mg, La, Ce, Y) layered double hydroxides for dimethyl carbonate synthesis by transesterification of methanol with propylene carbonate

Abstract

Composite solid base catalysts derived from Ca-M-Al (M = Mg, La, Ce, Y) layered double hydroxides (LDH) were synthesized, characterized and applied to the transesterification of methanol with propylene carbonate. X-ray diffraction analyses of the catalysts show that all of the catalysts were in the form of composite oxides. Compared with the Ca-Al LDH catalyst, the specific surface areas and pore volumes of the catalysts were increased with the introduction of Mg, La or Ce. The catalytic performance of these catalysts increases in the order of Ca-Y-Al < Ca-Al < Ca-Ce-Al < Ca-La-Al < Ca-Mg-Al, which is consistent with the total surface basic amounts of these materials and the formation of especially strong basic sites following modification with Mg and La. The Ca-Mg-Al catalyst shows the highest (Ca+Mg):Al atomic ratio, indicating that it likely contains more unsaturated O2– ions, providing it with the highest concentration of very strong basic sites. The recyclability of these catalysts is improved following the addition of Mg, La, Ce or Y, with the Ca-Mg-Al maintaining a high level of activity after ten recycling trials. X-ray diffraction analyses of fresh and used Ca-Mg-Al demonstrate that this catalyst is exceptionally stable, which could be of value in practical applications related to heterogeneous catalysis.