Influence of the surface oxygenated groups of activated carbon on preparation of a nano Cu/AC catalyst and heterogeneous catalysis in the oxidative carbonylation of methanol

Coconut shell activated carbon (AC) is treated by nitric acid and used as a support to prepare nano-copper heterogeneous catalysts for oxidative carbonylation of methanol to dimethyl carbonate. AC supports and their corresponding catalysts are characterized intensively by BET, XPS, XRD, TEM, N2O chemisorption, CO adsorption, and TPR. The results show that the concentrations of nitric acid do not significantly changes the specific surface area and textural property of AC. But the oxygenated groups which result in acidic properties, such as lactone, carboxyl and phenol groups, are formed on AC surface during the acid treatment process and increase with the increasing concentration of nitric acid. The increased surface oxygenated groups not only influence the dispersion but also the valence distributions of copper species. When copper supported on the AC treated by 4 M HNO3, the Cu/AC catalyst shows the optimal catalytic performance for oxidative carbonylation of methanol to dimethyl carbonate, which might be ascribed to the highest dispersion of Cu+ and Cu0 species. The average conversion of methanol and space-time yield of DMC (STYDMC) within 10 h for the catalyst have reached 9.2% and 229 mg g−1 h−1, respectively. The deactivation of Cu/AC catalysts is attributed to the agglomeration of copper species. Besides, the STYDMC of per S(Cu+ + Cu0) for the acid treated Cu/AC catalysts is very similar and less than that of the original Cu/AC catalyst which may be induced by the AC surface oxygenated groups itself but not the ratio of Cu+/Cu0.