Mesoporous Zr-Beta zeolites prepared by a post-synthetic strategy as a robust Lewis acid catalyst for the ring-opening aminolysis of epoxides

Abstract

Mesoporous zirconosilicate, stannosilicate, and titanosilicate with the BEA structure framework have been prepared from the commercially available Beta zeolite via acid–alkaline treatments and subsequent dry impregnation of appropriate organometallic precursors. N₂ adsorption–desorption isotherms and TEM observations confirm that alkaline treatment can induce desilication to create intra-crystalline mesopores from the partially dealuminated Beta sample. The incorporation of Zr species into the zeolite framework at formed silanol defect sites is monitored by infrared and ¹H MAS NMR spectroscopy. Characterization results from UV-vis and XPS reveal that the majority of the incorporated Zr species exist in the form of tetrahedral Zr(IV) in the zeolite framework. The creation of Lewis acid sites with moderate acid strength upon Zr incorporation is confirmed by FTIR spectroscopy with pyridine adsorption. The as-prepared mesoporous Zr-Beta exhibits a remarkable catalytic activity and regio-selectivity to β-amino alcohols in the ring-opening aminolysis of epoxides, and the presence of mesopores can promote the reaction to a great extent through enhanced mass transfer. The impacts of the Lewis acidity of the catalysts, the basicity of amines and adsorption of reactants on the ring-opening aminolysis of epoxides are discussed in detail.