Preparation of KF–La2O2CO3 solid base catalysts and their excellent catalytic activities for transesterification of tributyrin with methanol

Abstract

A series of 25% KF–La₂O₂CO₃ catalysts (25-KF–LOC-x, x = 673, 723 and 773) were prepared at different calcination temperatures, which were tested as basic catalysts for the transesterification of tributyrin with methanol to produce methyl butyrate and characterized by means of XRD, SEM, CO₂-TPD, FTIR, XPS and XRF. It was found that the calcination temperature greatly influences the catalytic activity, and its order is 25-KF–LOC-673 < 25-KF–LOC-723 < 25-KF–LOC-773. Especially, the 25-KF–LOC-773 catalyst exhibits a very high activity, and the conversion of tributyrin is nearly 100%, the yield of methyl butyrate reaches 94% at 308 K. The activation energy of the 25-KF–LOC-773 catalyst is as low as 55.03 kJ mol⁻¹. The excellent catalytic activity of the 25-KF–LOC-773 catalyst can be attributed to the largest amount of surface hydroxyl among these 25-KF–LOC-x catalysts. The results indicate that the Brønsted base is the main active site at low reaction temperature. The recycling use and stability have been investigated over the 25-KF–LOC-773 catalyst. The results indicate that the 25-KF–LOC-773 catalyst has a high stability after being stored for 90 days. The deactivation of the used 25-KF–LOC-773 catalyst at 308 K is due to the loss of hydroxyl on the surface. However, the conversion of tributyrin can reach 91%, and the yield of methyl butyrate also can achieve 64% when the transesterification reaction is performed at 338 K over the second used 25-KF–LOC-773 catalyst. It indicates that the second used 25-KF–LOC-773 catalyst still possesses good catalytic activity at the higher reaction temperature due to the unchanged strong Lewis basic sites provided with surface oxygen anions.