Direct synthesis of HZSM-5 from natural clay

Highly crystalline HZSM-5 zeolite was directly synthesized through the steam-assisted conversion (SAC) approach using kaolin as the raw material, where NH3 center dot H2O was used as an alkaline vapor source. The catalytic performance of the obtained HZSM-5 with SiO2/Al2O3 ratios from 25.67 to 80 was investigated for converting methanol to light olefins (MTO). The results indicated that NH3 center dot H2O provided alkalinity to dissolve the raw materials and NH4+ cations to balance the charge of the framework. Highly crystalline HZSM-5 with crystal size in the range of 0.8-1 mu m was obtained within 1.0 h at 190 degrees C. The obtained HZSM-5 possessed high S-BET (above 440 m(2) g(-1)) and high total pore volume (above 0.3 cm(3) g(-1)). The acidity of the HZSM-5 was affected by the SiO2/Al2O3 molar ratio and residual metallic elements (such as Fe, Ti, Ca, P, etc.) in the leached metakaolin. The existence of the metallic elements similarly affected HZSM-5 modified with metal cations. HZSM-5 with a higher SiO2/Al2O3 molar ratio was favourable for the formation of C2-C4 olefins. The selectivity of C2-C4 olefins reached 68% when the SiO2/Al2O3 molar ratio was 68.79. This productive and facile method is inexpensive because the ammonium and calcination ion exchange processes are unnecessary.