Promotional effect of transition metal doping on the basicity and activity of calcined hydrotalcite catalysts for glycerol carbonate synthesis

A series of transition metal doped hydrotalcites (HT-M) were prepared by using the “memory effect” of hydrotalcites (HT). Further calcination yields mixed oxides with more open structure and tunable basicity. The basicity of the calcined hydrotalcites (HTC-M) strongly depends on the type of transition metal and calcination temperature. The resulting HTC-M materials were used as solid base catalysts and evaluated in the transesterification between glycerol and dimethyl carbonate without using organic solvent. The correlation between the basic properties of the solid catalysts and the catalytic performance was investigated. The activity of HTC-M catalysts was demonstrated to be proportional to the surface density of basic sites. The HTC-Ni calcined at 500 °C exhibited maximum activity, which is about 10 times higher than uncalcined HT precursor for the transesterification reaction. The promotional effect of Ni2+ doping could be attributed to the enhancement of the base strength of all three types of basic sites of the calcined hydrotalcite. The HTC-Ni catalyst can be readily recycled while maintaining high catalytic activity and selectivity of glycerol carbonate.