The reaction of urea with ZnO was investigated by FTIR and TPD. It was found that urea was thermally decomposed into isocyanic
acid on ZnO, and the adsorbed isocyanic acid reacted with ZnO to form zinc isocyanate. Catalytic evaluation showed that ZnO
had high activity towards urea methanolysis in a batch reactor, and zinc element and isocyanate were all detected in the product
solution. Furthermore, the soluble zinc content was proportional to the DMC yield. Sample analyses suggested that the soluble
zinc existed in the form of Zn(NCO)2(NH3)2, which originated from the reaction of ZnO with urea. It was the complex (not ZnO) that catalyzed the urea methanolysis.
Based on these observations, a possible mechanism was suggested.