Intriguing Catalyst (CaO) Pretreatment Effects and Mechanistic Insights during Propylene Carbonate Transesterification with Methanol

Transesterification of cyclic carbonates to dimethyl carbonate using metal oxide (CaO, BaO and SrO) catalysts is reported with the objective of understanding the pretreatment effect of methanol and cyclic carbonates on catalytic performance. Stirred batch reactor experiments reveal that with untreated CaO as catalyst, significant induction time was observed. The induction time was eliminated upon CaO pretreatment with methanol and the transesterification activity increased from 11 to 947 h–1. In contrast, pretreatment with PC resulted in a prolonged induction time and rate inhibition. Further, although the methanol pretreatment effects were found to be irreversible, those with PC were reversible upon methanol treatment. Pretreatment of CaO with other cyclic carbonates including ethylene carbonate (EC) and 1,2-butylene carbonate (BC) showed similar transesterification trends as PC. Based on these experimental results and complementary catalyst characterization results using SEM, CO2-TPD, XRD, FT-IR, XANES and 13C NMR, a possible reaction mechanism that involves methoxy species as the key intermediate is proposed. In the last, recycle experiments were carried out verified that the catalyst is stable during successive cycles of substrate addition. These results provide new fundamental insights into transesterification catalysis and guidance for rational catalyst design and activation.