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

Abstract

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, NH 3 -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 MoO 3 reduced the distribution of acidic site density of LZ-5. The reaction sites of ethylbenzene, m-xylene 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, m-xylene and o-xylene. High performance xylene isomerization catalysts (2SZ/8LZ) were obtained by a simple mixture of the dealkylation catalyst (Pt–3Si/SZ-5) and the isomerization catalyst (Mo/LZ-5). It demonstrates excellent catalytic activity in mixed xylene isomerization reactions. • The SiO 2 deposition effectively covers the acidic sites on the external surface and adjusts the pore-opening size. • The modification of MoO 3 reduces the acidic site density of LZ-5 with large crystal size and improves the MX and OX isomerization activity. • The ethylbenzene conversion rate, xylene loss rate and PX yield of 2SZ/8LZ reached 74.9%,1.41% and 23.3% at 380 °C, respectively.