Post-synthesis of Zr-MOR as a robust solid acid catalyst for the ring-opening aminolysis of epoxides

Abstract

Zirconosilicate with the MOR topology (Zr-MOR) was successfully prepared using a two-step post-synthesis strategy from pre-dealumination of a H-MOR zeolite and subsequent dry impregnation of Cp₂ZrCl₂. The incorporated Zr species mainly existed in the form of isolated tetrahedrally coordinated Zr in the MOR framework. It was found that the mechanism of the post-synthetic incorporation of Zr involved interaction between the Cp₂ZrCl₂ molecules and silanols at defects generated by steaming and acid treatment. In comparison with Ti- and Sn-silicate analogues, the as-synthesized Zr-MOR zeolite showed high activity and regioselectivity in the ring-opening aminolysis of epoxides to β-amino alcohols under ambient and solvent-free conditions, which was related to the impact of the Lewis acid sites of the catalysts, the basicity of the amines and competitive adsorption of the reactant molecules. Moreover, the Zr-MOR zeolite could be reused at least five times without loss of activity and regioselectivity.