The effect of Si/Al ratio of ZSM-5 zeolite on its morphology, acidity and crystal size

ZSM-5 zeolite crystal with different Si/Al molar ratios in the range of 10-50 was synthesized using sodium silicate, aluminum sulfate and tetrapropylarmmonium bromide (TPA-Br) as the organic template. The produced samples were characterized using XRD, FT-IR, SEM and EDX techniques. All synthesized samples were found to be ZSM-5 zeolite as confirmed by XRD and supported by FT-IR. SEM results showed that ZSM-5 synthesized with different Si/Al molar ratios had different morphologies and particle sizes. It was found that the average ZSM-5 crystal size increased as Si/Al molar ratio increased. Thermogravimetric-difference thermal analysis (TG-DTA) technique was also used to measure the amount of template occluded inside the crystal pore. The synthesized Na-ZSM-5 was transformed into its acidic form, i.e., H-ZSM-5 using ion exchange method with ammonium nitrate solution. The H-ZSM-5 acidity was determined by NH(3)-TPD. These results showed that different Si/Al molar ratios have effect on surface acidity of samples. The surface areas of the H-ZSM-5 were measured using BET method and the results showed that, decrease in Si/Al ratio, decreased the surface area. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim