Transition metal-modified mesoporous Mg-Al mixed oxides: Stable base catalysts for the synthesis of diethyl carbonate from ethyl carbamate and ethanol

Abstract

A series of transition metal-modified hydrotalcite precursors (HT-M, M=Cr3+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+ and Zn2+) were prepared by using the “memory effect” of Mg-Al hydrotalcite. Then, the mixed oxides with different composition were obtained by thermal decomposition of as-prepared hydrotalcite precursors at 773K, and their physicochemical properies were characterized by thermogravimetry and differential thermogravimetry (TG-DTG), X-ray diffraction (XRD), N2 adsorption–desorption, X-ray photoelectron spectroscopy (XPS), scanning electron micrograph (SEM) and CO2 temperature-programmed desorption (CO2-TPD) technique. It was found that the mesoporous structure was formed during calcination. More important, the basicity of the calcined hytrotalcites (HTC-M) samples was depended on the type of transition metal. Simultaneously, they were used as solid base catalysts and evaluated for the synthesis of diethyl carbonate (DEC) from ethyl carbamate and ethanol. Among them, HTC-Mn exhibited maximum activity with the DEC yield of 56.7% under optimum reaction conditions. Then, the correlation between their basic properties and catalytic performance was studied in detail for the HTC-M catalysts. Furthermore, HTC-Mn catalyst could be readily recycled while maintaining high catalytic activity toward this reaction.