Surface Structure and Catalytic Performance of CuCl/SiO_2-Al_2O_3 Catalysts for Methanol Oxidative Carbonylation
LI Zhong, MENG Fanhui, REN Jun, ZHENG Huayan, XIE Kechang(Key Laboratory of Coal Science and Technology, Ministry of Education and Shanxi Province, Taiyuan University of Technology, Taiyuan 030024, Shanxi, China)
Aluminum was doped into amorphous silica gel to modify its surface structure. The obtained SiO2-Al2O3 support was used to prepare the CuCl/SiO2-Al2O3 catalyst by solid-state ion exchange, and the catalyst activity for liquid-phase oxidative carbonylation of methanol to dimethyl carbonate was investigated. The results showed that the prepared SiO2-Al2O3 support kept the amorphous structure of the silica gel. The BET specific surface area of the silica gel was decreased to 200 m2/g, and the surface acid sites (including Brnsted acid sites) were increased. In the CuCl/SiO2-Al2O3 catalyst, CuCl was not only dispersed on surface but also was ion exchanged with surface Brnsted acid sites of the SiO2-Al2O3 support to form Cu+ species, which resulted in a decrease in BET specific surface area to 148 m2/g. These two kinds of Cu+ species on the catalyst surface were both active centers for the oxidative carbonylation of methanol to dimethyl carbonate. When the catalyst was prepared with Si/Al molar ratio of 5 and was calcined at 500 ℃, the selectivity and space-time yield of dimethyl carbonate reached 74% and 1.27 g/(g·h), respectively.