Synthesis of dipropyl carbonate over calcined hydrotalcite-like compounds containing La

• Hydrotalcite-like compounds were used as base catalyst precursors.
• Influence of the La content on the formation of hydrotalcite-like phases of the LaMgAl hydroxycarbonates was investigated.
• Addition of La enhanced the moderate strength base while the precursor kept hydrotalcite structure.
• Moderate strength base site was the active site for this reaction.

Dipropyl carbonate (DPC) was selectively synthesized via transesterification of dimethyl carbonate (DMC) and n-propanol over Mg–Al composite oxide containing La catalysts. The catalysts were prepared by calcining the precursors of hydrotalcite-like compounds (HTLcs) from co-precipitation method. The effect of La content (nMg:nAl:nLa = 3:1:x) in the catalyst on the synthesis of DPC was investigated. And the catalyst exhibited the highest catalytic activity when x was tuned to 0.7. Under the optimized reaction conditions, the DMC conversion and DPC selectivity were 98.4% and 95.4%, respectively. These catalysts were characterized by thermogravimetry differential thermal analysis (TG-DTA), X-ray diffraction (XRD), nitrogen adsorption–desorption, Fourier transform infrared (FT-IR), temperature programmed desorption with CO2 (CO2-TPD) and scanning electron micrograph (SEM). It was clarified that the amount of basic sites of moderate strength, formed by chelating bidentate carbonate, was enhanced with the La content increasing until x = 0.7, which were the catalytically-active sites for this reaction. But when La content x reached 1.0, these sites were transformed to bridging bidentate carbonate, leading to a loss of the catalytic activity to some extent. These findings indicated that La content controlled the catalytic performance of the composite oxides catalysts via structure change of the basic sites. The catalyst was easily prepared and handled, easily separated from the reaction medium and could be reused many cycles.

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