The influence of cation, anion and water content on the rate of formation and pore size distribution of zeolite ZSM-5

L Petrik

doi:10.4102/sajs.v105i7/8.37

Abstract

Rapid synthesis and high mesoporosity of ZSM-5 is promoted by altering a fixed molar regime with respect to anion and cation type and water content only. This study shows that merely changing the cation and anion types, accompanying the hydroxide and alumina (Al) sources, respectively, has an impact on the characteristics of ZSM-5. Under identical and replicated preparation and testing conditions, the synthesis time, Al incorporation, product yield, acidity, morphology, pore size distribution and catalytic activity were affected. An ion pair combination of Na + /NO3 - allowed the formation of ZSM-5 with enhanced mesoporosity withi n3hi n a high-water environment, whereas ZSM-5 prepared with the Na + /SO4 2- combination had enhanced n-hexane cracking activity. Use of a K + /NO3 - ion pair combination in a high-water environment resulted in slower time of formation and larger ZSM-5 crystals with extra-framework Al, loss of acidity, lower surface areas and reduced n-hexane cracking activity. The sulphate anion inhibited the incor- poration of Al in ZSM-5 products in low-water environments. Low- water levels increased the time of formation of ZSM-5. : zeolite ZMS-5, synthesis, cation, anion, acidity, poros- ity, extra-framework aluminium, n-hexane cracking activity, sul- phate, nitrate

Highlights

Apart from microwave-assisted techniques,[1] few studies report or give a rationale for rapid crystallisation of zeolites
Inui[2] reported a method for rapid synthesis of zeolite ZSM-5 (MFI-type zeolite according to IUPAC nomenclature) using an involved pre-synthesis preparation technique, in which filtered, ball-milled, aged precursor gels containing high amounts of NaCl were reintroduced into fresh mother liquors and subjected to hydrothermal synthesis for 0.5 h
It is difficult to decouple the relative effects of each variable on catalyst quality, or to correlate changes in catalytic activity of ZSM-5 with synthesis variables, when molar regimes and sources of chemicals varied from study to study

Summary

Introduction

Apart from microwave-assisted techniques,[1] few studies report or give a rationale for rapid crystallisation of zeolites. Inui[2] reported a method for rapid synthesis of zeolite ZSM-5 (MFI-type zeolite according to IUPAC nomenclature) using an involved pre-synthesis preparation technique, in which filtered, ball-milled, aged precursor gels containing high amounts of NaCl were reintroduced into fresh mother liquors and subjected to hydrothermal synthesis for 0.5 h. Few investigations were carried out in comparable molar regimes in systematic studies concerning the influence of cation and anion type on the rate of formation, morphology and catalytic activity of ZSM-5. It is difficult to decouple the relative effects of each variable on catalyst quality, or to correlate changes in catalytic activity of ZSM-5 with synthesis variables, when molar regimes and sources of chemicals varied from study to study. Different preparation methods for ZSM-5 may result in the introduction of diffusional constraints and changes in shape-selectivity of the working catalyst due to changes such as the accidental introduction of extra-framework aluminium (EFAl), or altered crystal morphology, pore volume distribution

Methods

Results

Conclusion