Effect of Si/Al Ratio of Mesoporous Support on the Structure Evolution and Catalytic Performance of the Cu/Al-HMS Catalyst

Abstract

Copper-containing mesoporous Al-HMS catalysts prepared via the deposition−precipitation method have been found to be highly efficient in the catalytic hydrogenation of dimethyl oxalate (DMO) to ethylene glycohol (EG). Besides the Al chemical environment, the Si/Al ratios of the mesoporous support show remarkable effect on the catalytic performance. The DMO hydrogenation activity increased with the increasing of Al content in the support, and the highest catalytic activity was obtained when the Si/Al ratio of the support reached 25. A series of catalysts with different Si/Al ratios were characterized by N2 adsorption−desorption, X-ray diffraction, temperature-programmed reduction, N2O titration, NMR, and X-ray photoelectron spectroscopy. 27Al NMR shows that the tetrahedral coordination Al species that exists in the framework of the support could enhance the catalytic performance while the extraframework Al species would decrease the catalytic properties. The structural defects produced in the Al-containing mesoporous support play an important role in improving the dispersion of active copper species and enhancing the interaction between the copper species and support. On the basis of the characterizations, the copper species on calcined CuO/Al-HMS samples and reduced Cu/Al-HMS samples were assigned. The improvement of the catalytic performance with proper Si/Al ratio may be ascribed to the increasing defect sites associated with Al cations and the electronic promotion.