关键词: 固体酸, 多相催化, 铜催化剂, 氧化锌, 固体离子交换

Abstract: Two novel solid acids of SO₄^2-/ZnO and S₂O₈^2-/ZnO were prepared by impregnating H₂SO₄, (NH₄)₂S₂O₈ solution respectively on amorphous zinc oxide and calcining at 500—600 ℃, and then used as carriers to prepare Cu(Ⅰ)/SO₄^2-/ZnO and Cu(Ⅰ)/S₂O₈^2-/ZnO catalysts via solid-state ion-exchange. The solid acids and catalysts were characterized by XRD, FTIR, TPD and TPR. It is observed that Zn₃O(SO₄)₂ was formed during the preparation of the solid acids, and both of Lewis and Brnsted acid sites were formed on SO₄^2-/ZnO and S₂O₈^2-/ZnO. NH₃-TPD shows that both SO₄^2-/ZnO and S₂O₈^2-/ZnO were very strong solid acids because the temperature of NH₃ desorption peaks were above 543 ℃. It is suggested by molecule structure analysis that the form of acid sites is due to the strongly electronic inductive effect of SO₄^2-, the bridge-coordination complex of ZnO and SO₄^2- causes the formation of Brфnsted and Lewis acid sites on the surface, but the chelate-coordination complex of ZnO and SO₄^2- has not any contribution to acid sites. Prepared by solid-state ion-exchange with the solid acids and CuCl at high temperature in N₂ follow, Cu(Ⅰ)/SO₄^2-/ZnO and Cu(Ⅰ)/S₂O₈^2-/ZnO catalysts, in which Cu(Ⅰ) was easy to be reduced, showed an excellent catalytic behavior in the oxidative carbonylation of methanol to dimethyl carbonate(DMC). Both of the catalysts showed high catalytic activity and selectivity: 98.13% selectivity of DMC based on methanol and 1.87 g/(g·h) space-time yield, respectively.

Key words: Solid acid, Heterogeneous catalysis, Copper-based catalyst, Zinc oxide, Solid-state ion-exchange