Effect of Cu location and dispersion on carbon sphere supported Cu catalysts for oxidative carbonylation of methanol to dimethyl carbonate

A series of novel composite catalysts consisting of carbon spheres with encapsulated copper species were synthesized by incipient wetness impregnation. To improve catalytic activity, Cu location on the hollow carbon spheres was tuned by ultrasonic-assisted impregnation. The location, dispersion and chemical structure of copper species were characterized by X-ray diffraction, Temperature-programmed reduction, Transmission electron microscopy, N2-physisorption, Atomic absorption spectroscopy, X-ray photoelectron spectroscopy and dissociative N2O adsorption measurements. The results showed that hollow mesoporous carbon spheres have uniform mesopores, which were more favorable to the confinement and dispersion of the active species than solid carbon spheres. The catalyst with Cu species highly dispersed in the mesopores of hollow carbon spheres exhibited superior catalytic performance compared with those with Cu species located outside the support or inside the hollow interiors. The catalyst with ultrafine Cu particles of 2 nm in the mesopores of the 200 nm carbon sphere exhibited a dimethyl carbonate Space-Time Yield of 218.4 mg·g−1cat·h−1, much higher than traditional activated carbon and ordered mesoporous carbon supported Cu catalysts. Interestingly, copper species in the cavity showed high autoreduction ability in spite of poor dispersion after activation, and this catalyst is anticipated to achieve better activity by improving Cu dispersion.