Transesterification of Propylene Carbonate with Methanol Using Fe–Mn Double Metal Cyanide Catalyst

A highly active and selective heterogeneous catalyst consisting of Fe–Mn double metal cyanide is reported for the transesterification of cyclic carbonates with methanol. Fe–Mn double metal cyanide complex with a Fe/Mn metal ratio of 8 was found to provide significantly higher TOF and stability for transesterification of propylene carbonate with methanol to dimethyl carbonate. The experimental results showed that Mn content has a significant influence on the catalytic activity. TEM and XRD analyses suggested that Fe–Mn complex represents a cubic crystalline structure. XPS analysis showed that all Fe exists in Fe2+ state. However, for the Mn element, 86.8% of Mn exists in Mn2+ state with only 13.2% in Mn4+ state. Furthermore, FTIR and DRIFT UV–vis results verified the formation of a new mixed-metal complex of ferrocyanide moiety and Mn ions via bridging cyanide ligands. NH3-TPD results showed that Fe–Mn double metal cyanide has a strong acidity, which correlates to the high activity of Fe–Mn double metal cyanide complex. The effects of catalyst loading, methanol/PC ratio, temperature, and different cyclic carbonate substrates (ethylene carbonate, propylene carbonate, and 1,2-butylene carbonate) on the initial reaction rate as well as concentration–time profiles are reported. Unique feature of this catalyst is also nonleaching characteristics during reaction and higher TOF unlike the conventional catalysts such as CaO. Compared with the results from Fe and Mn alone as catalysts, Mn in this complex was proposed to be acting as active species, while Fe acting as a metal-dispersing agent and a stabilizer of the cyano-bridged complex and ensures a truly heterogeneous catalyst. On the basis of this, a possible reaction mechanism was proposed. The results presented in this work provide useful insights on the reaction mechanism of transesterification using Fe–Mn double metal cyanide catalysts, which may also be useful to guide rational design of improved catalysts and process for transesterification of cyclic carbonates.