Lead-containing Beta zeolites as versatile Lewis acid catalysts for the aminolysis of epoxides

Abstract

Pb-Beta, a heteroatom zeolite containing out-size atoms of lead, has been successfully prepared via a scalable post-synthesis strategy composed of dealumination of H-Beta to create associated silanol and subsequent dry impregnation of the resulting Si-Beta with lead nitrate. The incorporated lead species exist in the form of well-isolated tetra-coordinated Pb2+ ions with open configurations, as revealed by the characterization results from high angle annular dark filed scanning transmission electron microscopy (HAADF-STEM), UV-Vis, X-ray photoelectron spectroscopy (XPS) and 29Si solid-state magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. Sufficient Lewis acid sites with moderate acid strength are created by lead incorporation into zeolite framework, as confirmed by the temperature-programmed desorption of ammonia (NH3-TPD). The as-prepared Pb-Beta Lewis acid zeolites exhibit remarkable catalytic activity in the ring-opening aminolysis of epoxides to β-amino alcohols with high regio-selectivity. The presence of wide-open lead sites can promote the simultaneous activation of epoxide and amine substrates and, therefore, catalyze the aminolysis of epoxides with strong basic amines, e.g. butylamine.