The direct synthesis of dimethyl carbonate by the oxicarbonylation of methanol over Cu supported on carbon nanotube

Abstract

The activity of Cu/MWCNT and Cu–Ni/MWCNT catalysts was investigated in the synthesis of dimethyl carbonate (DMC) by oxidative carbonylation of methanol. The catalysts were prepared via conventional incipient wetness impregnation technique. The samples were characterized by X-ray photoelectron spectroscopy (XPS), and DRIFT. The reaction was carried out in a continuous flow system at atmospheric pressure at 393K. The main products were methyl formate (MF), DMC and CO2. The methanol conversion on Cu/MWCNT achieved a steady state value after 2h, but on Cu–Ni/MWCNT the conversion decreased continuously. The DMC selectivity was more than 30% and the yield was 1.2% on Cu/MWCNT. Based on the XPS data we can establish that copper reduced to its metallic form during reduction but oxidized in the reaction mixture, and is mostly in the Cu+ state, with some Cu2+ also present on the surface at the beginning of the reaction though its ratio decreased in time. We assume that the DMC formation rate depends on the surface concentration of oxidized Cu. Based upon the FTIR data adsorbed DMC is present on the surface of the Cu/MWCNT catalyst during the catalytic reaction but on Cu–Ni/MWCNT sample only methyl formate was detected in the gas phase.