Effect of Mixing Order of Si and Al Sources on the Inner Architecture and Catalytic Performance of ZSM-5 Zeolites

The performance of zeolites in catalysis and adsorption is closely related to their inner architecture beneath the crystal surface, which however remains less studied due to characterization limitations. Here we report the synthesis of two ZSM-5 zeolite samples by changing only the order of mixing of Si and Al sources, resulting not only in morphological differences of the zeolite crystals but most importantly in defined distinction in their inner architecture. The spatial Si and Al distributions and structural properties of the ZSM-5 zeolite crystals were characterized by high-resolution microscopy under chemically unbiased defect-selective NH4F etching. The Al-zoning and structural features in the ZSM-5 zeolite crystals were explained by the biased nucleation in the Si-rich aluminosilicate amorphous precursor followed by multistage crystal growth in a heterogeneous feedstock. This observation was associated with the different solubility and reactivity of the microscopic aluminosilicate domains with various Si/Al ratios in the amorphous precursors. The zeolites with diverse structural properties showed a high cracking activity in n-hexane cracking reaction and different activity, stability, and product selectivity in the ethylene dehydroaromatization (EDA) reaction. The comprehensive understanding of the zeolite synthesis history and their performance in the EDA reaction revealed the chemical mixing-dependent synthesis-structure-performance correlation of the zeolite catalyst.