Silylation with trimethylchlorosilane and subsequent analyses of the products by 29Si CP MAS NMR is an appropriate method for the characterization of terminal groups in ZSM-5. It can be shown that the terminal groups are clustered and belong to gaps of missing T-atoms (Si or Al). These gaps are part of regularly 4-membered and larger rings in the lattice of ZSM-5. During prolonged heat treatment of ZSM-5 the amount of internal terminal groups decreases. We propose a T-jump mechanism of the gaps resulting in a migration of the terminal groups towards the external surface of the zeolite particles.
|Studies in Surface Science and Catalysis