Effect of the structure on both the catalytic activity and hydrothermal stability of ZSM-5 in the cracking of naphtha

In the present study, the influence of ZSM-5 zeolite structure on the catalytic properties and hydrothermal stability is investigated in detail. By XRD, N₂ adsorption/desorption, NH₃-TPD, SEM, ²⁷Al MAS NMR, XPS, DR-UV and ZLC characterizations, it has been confirmed that a nano-sized ZSM-5 (SZ) exhibits the higher external surface area (more pore mouths) and shorter pore channels than the micro-sized ZSM-5 (CZ), which contributes to the better diffusivity of reactants/products resulting in better accessibility of acid sites in channels by reactants and less secondary reactions of products. Furthermore, another advantage of SZ sample is reflected in the less Al pairs and more uniform Al distribution, which is favorable to the hydrothermal stability of zeolite. Especially, the smaller particle size of SZ can also improve the diffusion efficiency of doping P species into the interior pore, which further increases the hydrothermal stability of P/SZ sample due to the strengthened P-Al interaction. As a result, the P/SZ catalyst exhibits a simultaneous increase in both catalytic activity and hydrothermal stability in the catalytic cracking of naphtha compared to the P-modified CZ.