Solvent- and OSDA-Free Synthesis of ZSM-5 Assisted by Mechanochemical and Vapor Treatments

Various synthesis methods of zeolites have been established. Hydrothermal synthesis method with organic structure directing agent (OSDA) has been widely applied in zeolite synthesis. However, this method has some big problems in terms of industrial and environmental aspects: OSDA is expensive and thermally decomposed OSDA produces air pollution; and the yield of zeolite crystals per reactor volume is low due to the presence of solvent. We hence synthesized ZSM-5 (MFI-type zeolite) in the absence of both solvent and OSDA to overcome these problems. Briefly, the starting materials including silica powder, sodium aluminate, sodium hydroxide and a small amount of seed crystals (ZSM-5) were mixed together and grinded using a ball mill. Then the milled powder was crystallized under a steam atmosphere by varying crystallization time. We found that an MFI phase started to appear after 12 h and the formation of pure ZSM-5 crystals was completed after 24 h. Our method provides a simpler and efficient process of zeolite synthesis in an environment-friendly manner than those of any conventional solvent methods, which will promise to promote mass production of a variety of zeolites.