Investigation of supported Zn(OAc)2 catalyst and its stability in N-phenyl carbamate synthesis

Abstract

Zn(OAc)2 was found to give excellent catalytic performance for methyl N-phenyl carbamate (MPC) synthesis from aniline and dimethyl carbonate (DMC). However, after being used for only once it tended to lose activity because of the formation of ZnO by the reaction of Zn(OAc)2 and methanol. Zn(OAc)2/SiO2 was prepared by incipient impregnation and it gave excellent catalytic performance in MPC synthesis, on which aniline conversion and MPC yield were 98.1% and 93.8%, respectively. And Zn(OAc)2/SiO2 was found to be more stable than Zn(OAc)2 during the reaction. When Zn(OAc)2/SiO2 was used for the fifth time, aniline conversion and MPC yield were found to be 64.3% and 38.1%, respectively. The Zn(OAc)2/SiO2 catalyst was characterized by TG-DTA, ICP, FTIR, XRD and XPS. The characterization results suggested that the deactivation of Zn(OAc)2/SiO2 was also due to the formation of ZnO and there were two reasons for the improved stability of Zn(OAc)2/SiO2 catalyst. One was the formation of the Si–O–Zn bonds in Zn(OAc)2/SiO2 catalyst, which increased the steric hindrance of Zn and consequently retarded the reaction between Zn(OAc)2 and methanol. The other cause was the dehydration between methanol and the hydroxyl group on the SiO2 surface, which reduced the chance of a reaction between methanol and Zn(OAc)2.