Oxidative carbonylation of methanol to dimethyl carbonate over CuCl/SiO2–TiO2 catalysts prepared by microwave heating: The effect of support composition

Copper(I) chloride catalysts with a loading of 20 wt%, supported on silica–titania mixed oxides with Si/Ti ratios of 1, 5, 10 and 50 were prepared by conventional and microwave heating methods and tested in the oxidative carbonylation of methanol to dimethyl carbonate (DMC). X-ray diffraction (XRD), nitrogen adsorption, X-ray photoelectron spectroscopy (XPS) and thermal gravimetric analysis (TGA) were used to examine the bulk and surface properties of the CuCl/SiO2–TiO2 catalysts. Quantum-chemical calculations were performed to explore the interaction of CuCl with the silica–titania support. Microwave heating showed some significant advantages over the conventional heating method, with markedly reduced preparation temperature and time, and provided improved catalytic activity in the oxidative carbonylation of methanol. The catalytic behavior of CuCl/SiO2–TiO2 in the test reaction studied was strongly dependent on the support composition. Incorporation of tetrahedral Ti(IV) species into the silica matrix could enhance the interaction of copper species with the oxide support. The improved catalytic performance of CuCl/SiO2–TiO2 in the DMC synthesis can be understood by the existence of the strong coordination interactions between the Cu+ centers of CuCl and the bridging oxygen atoms at the Si–O–Ti bonds in the silica–titania support.

Quantum-chemical calculations on cluster models indicated that the interactions between CuCl molecules and the Si–O–Ti bonds lead to the formation of the relatively strongly bound O-complexes, in which the bridging oxygen atoms at Si–O–Ti bonds serve as electron-donating ligands to Cu+ centers of CuCl.Figure optionsDownload as PowerPoint slide