Catalytic synergistic effect of bis-ZSM-5 zeolite with different crystal sizes for xylene isomerization

High-performance xylene isomerization catalysts were prepared by physical mixing of two types of ZSM-5 after reasonable modification. Here, SZ/LZ catalysts were prepared by simple physical mixing of two modified Pt-3Si/SZ-5 and Mo/LZ-5 with different crystal sizes. The catalytic performance of the catalysts was evaluated in the mixed xylene isomerization reaction on a fixed bed. The catalysts were characterized by XRD, BET, SEM, TEM, XPS, Py-IR, NH3-TPD and probe molecular reactions. The results demonstrated that the deposition of silica finely adjusted the size of the pore opening and passivated the acid sites on the external surface of the SZ-5 zeolite. The loading of MoO3 reduced the distribution of acidic site density of LZ-5. The reaction sites of ethylbenzene, mxylene and o-xylene were precisely distributed by the 2SZ/8LZ catalyst. Optimizing the mixing ratio and reaction temperature of the catalysts further improved their synergistic catalysis. High EB conversion rate (74.9%), high PX yield (23.3%) and low xylene loss (1.41%) were obtained by controlling the reaction path of ethylbenzene, mxylene and o-xylene.

Automated summary

High-performance xylene isomerization catalysts were prepared by physically mixing and reasonably modifying ZSM-5. Silica deposition adjusted the pore opening size and passivated acid sites, while MoO3 loading reduced the distribution of acidic site density. Optimizing the catalyst's mixing ratio and reaction temperature further improved its synergistic catalysis, resulting in high EB conversion rate, high PX yield, and low xylene loss.