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 tetrapropylammonium 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 NH₃‐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. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)