Detection of the ‘invisible aluminium’ and characterisation of the multiple aluminium environments in zeolite USY by high-field solid-state NMR

The detection of all of the aluminium present in steamed zeolite H-Y catalysts by ²⁷Al MAS NMR at high field (18.8 T, 800 MHz for ¹H) is reported; further, it is shown that it is possible by ²⁷Al MAS and MQMAS measurements to clearly identify four separate aluminium environments characteristic of these materials and to unambiguously assign their coordinations.