Controllable preparation and toluene adsorption performance of ZSM-5 zeolites with different Si/Al ratios

This study employed a hydrothermal approach to prepare ZSM-5 zeolites with varying Si/Al ratios (Si/Al = 25, 50, 90, 165, 260, and pure siliceous). These were prepared in a controlled manner using ethyl orthosilicate as the silica source, sodium meta-aluminate as the aluminium source and tetra propylammonium hydroxide as the organic structure guiding agent. Adsorption tests were conducted on the samples using toluene as the adsorbate. Characterization results show that the crystallinity and particle size of zeolite increase as the Si/Al ratio rises, with significant changes in the pore structure. Toluene adsorption tests reveal that the synthesized ZSM-5 zeolites (varying Si/Al ratios) outperform the commercial ZSM-5 (Si/Al=50) adsorbent. Among these, the ZSM-5-260 zeolite exhibits the highest toluene adsorption capacity. Overall, the saturated adsorption capacity shows a non-monotonic trend with the Si/Al ratio, initially decreasing, then increasing, and finally decreasing again. This phenomenon is due to the fact that the adsorption performance of zeolites is influenced by both the Si/Al ratio and the pore structure.