Characterization and assessment of an enhanced CuY catalyst for oxidative carbonylation of methanol prepared by consecutive liquid-phase ion exchange and incipient wetness impregnation

Chloride-free CuY catalysts containing different oxidation states of Cu are prepared via three methods, namely, liquid-phase ion exchange, incipient wetness impregnation and a combined procedure of ion exchange and Cu(NO3)(2) impregnation. The objective is to develop effective catalysts for converting methanol to dimethyl carbonate through the oxidative carbonylation process. Microstructures and chemical compositions of as-produced samples are characterized by analytic chemistry methods such as temperature-programmed reduction of hydrogen (H-2-TPR), diffuse reflectance infrared transform spectroscopy (DIRFT) of CO adsorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic absorption spectroscopy (AAS) and transmission electron microscopy (TEM). The catalytic activities of as-produced samples are found to be distinct and associated with the oxidation states and locations of Cu2+/Cut The catalyst prepared by liquid-phase ion exchange contains Cu+ and Cu2+ in the smallcage and exhibits a low catalytic activity. The catalyst prepared by incipient wetness impregnation contains dispersed CuO (as the major Cu species) and Cu2+ in the sodalite units or hexagonal prisms (41% of the total Cu amount) and shows an improved catalytic performance. The catalyst prepared by the combined procedure contains an even greater amount of active CuO and Cu2+/Cu+ in the supercage and exhibits the best performance. It is concluded that Cu2+/Cu located in the supercage is the desired active center for oxidative carbonylation of methanol to produce dimethyl carbonate. (C) 2016 Elsevier B.V. All rights reserved.