Synthesis of mesoporous ZSM-5 using different saccharide meso templates and directing agents

Abstract

The mesoporosity of microporous ZSM-5 was synthesised by investigating the effect of different structure directing agents, and mesotemplates. In this study, tetrapropylammonium hydroxide (TPAOH) and tetrabutylammonium hydroxide (TPABr) were used as directing agents that could direct the formation of microporous ZSM-5 structure while saccharides (glucose and sucrose) were chosen as mesotemplates reagents. ZSM-5 zeolite was synthesized by hydrothermal method at 100oC with initial molar composition of Al₂O₃: 50SiO₂: 8TPA⁺: 1500H₂O : 20 saccharides. ZSM-5 was synthesized without using mesotemplate was also synthesized to make comparison with the templated samples. All synthesized samples were characterized by X-Ray Diffraction (XRD), Fourier Transform Infrared (FTIR) and nitrogen adsorption analysis. XRD results showed that only sample prepared by TPAOH as directing agent and sucrose as meso template (ZSM-5-SUC) formed ZSM-5 crystal phase while the rest of the samples showed dominantly amorphous material. Nitrogen adsorption analysis revealed all samples show high surface area (> 500 m²/g) with isotherm of the Type IV ie mesoporous characteristics. However analysis of the t-plot of all samples indicated that only ZSM-5-SUC sample a mixture of microporous and mesoporous characteristics with the mesoporous pore size distribution centred at 4.7 nm. Study showed that the present OH^- for the TPA ion is important in order to direct the formation of ZSM-5 microporous structure while sucrose facilitate the formation of mesoporosity of the ZSM-5 due to its mineralizing property. As compared to TPABr, the use of TPAOH as the directing agent is a good template because OH ion is able to transform Al³⁺ into tetrahedral aluminate ion which accounted for the formation of tetrahedral aluminosilicate framework of mesoporous ZSM-5 structure.