Solid-state crystallization, oxygen-vacancy rich mesopores and stable triad-silanol nests in ZSM-5 catalyst induced by electron-beam irradiation and calcination

Abstract

Mesopores and silanol nests are known two technological keys that essentially control the catalytic performance of ZSM-5 zeolite. However, designing and controlling them without using chemicals so that the produced ZSM-5 can have strongly enhanced catalytic properties and more importantly can be applied at industrial scale have still been a big challenge up to now. The present study employed the 10 MeV electron beam (EB) generated from an industrial linear accelerator to introduce both the O-vacancy rich mesopores and stable triad-silanol nests in ZSM-5. The structural modification of irradiated ZSM-5 samples was explored by using SEM and FTIR combined with positron annihilation spectroscopy (PAS) including positron annihilation lifetime (PAL), Doppler broadening (DB) of electron–positron annihilation energy and electron momentum distribution (EMD). Obtained results indicated that EB irradiation could recover the defective-crystal structure as well as intensively modify the structures of ZSM-5. In particular, the mechanism for the solid-state crystallization and the formation of the O-vacancy rich mesopores (maximum size of ∼4.5 nm) in ZSM-5 under the combined EB irradiation (10−110 kGy) and calcination (600 °C) was, for the first time, proposed. The mechanism for the formation of stable triad-silanol nests in the channels of irradiated and calcined ZSM-5 zeolites was also explored. The present study, therefore, opens a new research path of applying both EB irradiation and calcination to produce ZSM-5 with novel features for industrial catalytic application at large-production scale.

Keywords

• ZSM-5
• Electron beam irradiation
• Positron annihilation
• Solid-state crystallization
• Stable triad-silanol nests
• Oxygen-vacancy rich mesopores