Influence of nature of silica source on template-free synthesis of ZSM-5

Synthesis of ZSM-5 from template-free batches which preceded the preparation of template-free ZSM-5 layers on porous supports was studied to ascertain the effect of nature of silica source on the purity of template-free ZSM-5. Silicic acid and two colloidal silica sols were used as silica sources to prepare the template-free batches with a molar composition of 6.5Na(2)O:Al2O3:80SiO(2):3196H(2)O. One of the colloidal silica sols contained methanol as stabilizer while the other did not. The product purity and rate of crystallization increased when colloidal silica sols were used as silica source, however, use of silicie acid led to low purity and slow crystallization rate. The methanol in the colloidal silicic sol appeared to act as template to promote the crystallization and was occluded in the resultant ZSM-5 pores. The dissolution of the meta-stable ZSM-5 phase and formation of quartz was observed regardless of the nature of the silica source in case of prolonging the crystallization time more than 90 h at 200 degreesC