On the remarkable behaviour of zeolite Beta in acid catalysis

Zeolite Beta is developing into a major catalyst in organic chemicals conversion, contributing to low waste technology. In comparison with other zeolites, zeolite Beta possesses unique add properties which are related to local defects. These defects are generated when a tertiary building unit (TBU) is rotated 90 degrees around the c-direction with respect to the neighbouring TBUs in the same layer. The rotated TBU cannot connect properly with the adjacent layers. This results in T-atoms that are not fully coordinated to the framework, thereby creating potential Lewis-acid sites. The high stereoselectivity observed in the Meerwein-Ponndorf-Verley (MPV) reduction of 4-tert-butylcyclohexanone to the corresponding cis-alcohol and the absence of MPV reduction of the bulky probe molecule 1-(3,5-di-tert-butylphenoxy)propan-2-one on the external surface, indicate that Lewis-acid sites are mainly present in the micropore walls. By contrast, Bronsted-acid sites are present on the internal as well as the external surface.