The role of Mn doping in CeO2 for catalytic synthesis of aliphatic carbamate from CO2

Abstract

A novel highly active Mn-doping ceria heterogeneous catalyst (MnO_x–CeO₂) was prepared and dedicated to the catalytic synthesis of aliphatic carbamates from CO₂, aliphatic amines and methanol in one step. The as-obtained catalyst can attain a high yield of carbamate up to 82%, and can also be recycled at least four times through a simple procedure. It was observed that the Mn doping to ceria can alleviate the catalyst deactivation in consecutive catalytic recycles. In this regard, the role of Mn doping in the ceria in the synthesis of the aliphatic carbamates was investigated by means of X-ray diffraction (XRD), Raman spectra, specific surface areas (BET), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), CO₂-temperature programmed desorption (CO₂-TPD) and in situ diffuse reflectance infrared Fourier transform (DRIFT). The characterization demonstrated that the presence of MnO_x in the ceria can not only inhibit the formation of stable carbonate species on the surface of the catalyst but also promote the decomposition/consuming of the carbonaceous species during the synthesis of aliphatic carbamates so as to allow improvement of the recyclability of the catalyst.