Highly dispersed Cu supported on mesoporous Al-KIT-6 for oxidative carbonylation of methanol to dimethyl carbonate

Microporous NaY zeolite is a common support of Cu catalysts for oxidative carbonylation of methanol, but the dispersion of Cu species on NaY is usually subjected to its micropore size. Here, ordered mesoporous KIT-6 was employed as the support for Cu catalyst and Al was incorporated into its framework to increase the surface acidity, which eventually improves the surface exchange capacity and Cu dispersion. The evolution of the state of Cu species on KIT-6 was analyzed combined with control of Cu loading. The physicochemical properties of the supports and corresponding catalysts were characterized by N-2 adsorption-desorption, X-ray diffraction, ammonia temperature programmed desorption, Fourier transform infrared spectra, transmission electron microscopy, hydrogen temperature programmed reduction, and X-ray photoelectron spectroscopy. It was found that mesoporous KIT-6 showed better Cu dispersion than microporous NaY zeolite. Agglomerated CuO, dispersed CuO, and Cu2+ are the major Cu species observed on the catalyst surface. The increased surface acidic sites of KIT-6 by Al incorporation promoted the formation of Cu2+ and dispersion of CuO. With the increase in Cu loading, the Cu2+ content in the catalyst was decreased gradually along with increase in the bulk CuO. It was speculated that some exchanged Cu2+ could be transformed into highly dispersed CuO and even bulk CuO after calcination at a high Cu loading. Combined with the catalyst evaluation results, it was deduced that highly dispersed Cu2+ and CuO particles play significant roles in catalytic activity. The catalyst Cu/Al-K-10 achieved the highest space time yield of dimethyl carbonate of 135.4 mg/(g center dot h), which is 2.7 times the Cu/K-10 owing to its more dispersed Cu species. This laid the basis for preparing highly dispersed Cu species on mesoporous silica supports.