South African Journal of Science
On-line version ISSN 1996-7489
Print version ISSN 0038-2353
PETRIK, L.. The influence of cation, anion and water content on the rate of formation and pore size distribution of zeolite ZSM-5. S. Afr. j. sci. [online]. 2009, vol.105, n.7-8, pp.251-257. ISSN 1996-7489.
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 within 3 h in a high-water environment, whereas ZSM-5 prepared with the Na+/SO42- 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 incorporation of Al in ZSM-5 products in low-water environments. Low-water levels increased the time of formation of ZSM-5.
Keywords : zeolite ZMS-5; synthesis; cation; anion; acidity; porosity; extra-framework aluminium; n-hexane cracking activity; sulphate; nitrate.