Zinc oxide as the precursor of homogenous catalyst for synthesis of dialkyl carbonate from urea and alcohols

Zinc oxide (ZnO) was considered as an ideal heterogeneous catalyst for the synthesis of dialkyl carbonate from urea and alcohols in the previous works. However, according to the recent results of XRD, FTIR, TG–DSC and element analysis, ZnO was evidently found to be the precursor of homogenous catalyst Zn(NH3)2(NCO)2. Such a species could be formed via the coordination of NH3 to Zn(NCO)2, which originated from the reaction of ZnO with HNCO, the latter was the product of urea thermal decomposition.