Fabrication and characterization of ZrO2 and ZrO2/SiO2 catalysts and their application in the synthesis of methyl N-phenyl carbamate: a study of the reaction mechanism by using in situ FT-IR spectroscopy

The reaction of dimethyl carbonate (DMC) and aniline for the synthesis of methyl N-phenyl carbamate (MPC) over ZrO2/SiO2 catalyst was investigated. ZrO2/SiO2 showed the higher catalytic performance than that of ZrO2 because of the formation of Zr–O–Si bond, which increased the proportion of weak acid sites on the surface of ZrO2/SiO2 catalyst, and the weak Lewis acid sites were in favor of MPC synthesis. Furthermore, the reaction of DMC and aniline over ZrO2/SiO2 catalyst was studied by in situ Fourier transform infrared spectroscopy (FT-IR). When aniline adsorbed on catalyst, aniline lost protons of −NH2 to the surface O atom in Zr–O–Zr. As for DMC, there were two coordination mode of DMC with Zr4+ and the monodentate coordination by the carbonyl oxygen atom with Zr4+ was in the majority. The formation of MPC might be due to the nucleophilic attack on the carbonyl C atom of DMC by the N atom of adsorbed aniline after removing methanol. When the adsorbed aniline attacked the C atom on the methyl group of DMC, N-methylaniline (NMA) and monomethyl carbonate (MMC) was formed. MMC was unstable, and then the adsorbed methanol formed after removing CO2.