Template-Free Synthesis of ZSM-5: Effect of Precursor Composition on the Crystallinity and Crystal Morphology

A series of ZSM-5 samples were synthesized by template-free hydrothermal synthesis without adding seed crystals. When synthesis parameters such as temperature, duration, and molar ratio of components being equal, various silicas (specifically, Silica-Fumed from Sigma-Aldrich; Rosil-175 from the Bashkir Soda Company (BSC), Russia; Silica from the Salavat Catalyst Plant (SCP), Russia; and Aerosil-300 from Evonik, Germany) and of aluminum (Al(NO₃)₃∙9H₂O and NaAlO₂) were varied. In the presence of sodium aluminate, highly crystalline ZSM-5 samples were synthesized, whereas the use of aluminum nitrate led to an amorphous product due to accelerating aluminosilicate condensation. The ZSM-5 crystals prepared from various SiO₂ sources have different morphology, including the crystal size (ranging from 5.9 to 12.2 µm) and the aspect ratio (from 1.9 to 2.6). The ZSM-5 samples synthesized from available Russian-manufactured SiO₂ sources (Rosil-175 (BSC) and Silica (SCP)) in the presence of sodium aluminate consisted of crystals with average sizes of 5.9 and 6.9 μm, respectively, and a narrow particle size distribution (c_v < 20%).