Synthesis of ZSM-5 zeolite and silicalite from rice husk ash

Local rice husk was precleaned and properly heat treated to produce high purity amorphous SiO2 for use in the synthesis of ZSM-5 zeolite and silicalite by hydrothermal treatment (150 °C) of the precursor gels (pH 11) under autogenous pressure in a short reaction time (4–24 h). A wide range of SiO2/Al2O3 molar ratios (30–2075) and a small template content were employed to fully exploit the potential of rice husk ash (RHA). The mineralogical phases, morphology, specific surface area and pore volume of the synthesized products were investigated by XRD, FT-IR, SEM and BET analyses, respectively. Under the employed conditions, it was found that the gels with a low range of SiO2/Al2O3 molar ratios (<80) produced an amorphous phase to poorly crystalline ZSM-5 zeolite; those with a medium range (80–200) favored well crystalline ZSM-5 zeolite production with a large surface area; whilst those with a high range of SiO2/Al2O3 molar ratios (>200) yielded silicalite. The increase in Na2O content, which was derived from the addition of NaAlO2 to attain the desired SiO2/Al2O3 molar ratio of the gel, did not significantly enhance the crystallization rate, crystallinity, or yield of products. On the contrary, these properties were greatly affected by the increase in the SiO2/Al2O3 molar ratio.