The Nature of Active Copper Species in Cu-HMS Catalyst for Hydrogenation of Dimethyl Oxalate to Ethylene Glycol: New Insights on the Synergetic Effect between Cu0 and Cu+

Copper-containing mesoporous HMS catalysts prepared via a one-pot synthesis method based on sol-gel chemistry have been systematically characterized focusing on the effect of copper loading. Structural characterization of a series of different copper loading samples was performed by means of N-2 adsorption, X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, temperature programmed reduction, N2O titration, and X-ray photoelectron spectroscopy. It is concluded that the copper loading has a great influence on the pore structure of the catalyst. On the basis of the characterizations, the copper species on calcined CuO/HMS samples and reduced Cu/HMS samples were assigned. The synergetic effect between the Cu-0 and Cu+ is considered to be responsible for the enhanced catalytic performance in the hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG). The maximum ratio of Cu-0/Cu+ obtained via tuning the copper loading can result in the highest DMO hydrogenation activity and EG selectivity.