Silica-supported crystals of ZSM-5 zeolite: Effect of zeolite loading

The small crystals of ZSM-5 zeolite were synthesized and stabilized, inside the pores of silica gel support according to method described in>[1]. Changing the synthesis conditions, six samples with zeolite loading 5–90 wt.% and a reference 100% crystallinity zeolite, all with SiO₂/Al₂O₃ ratio ∼90 were prepared. Two stages of crystallization were identified: i) formation of small ZSM-5 zeolite crystals (0.025μm) in the supports mesopores and large zeolite crystals (4μm) on the outer surface of the silica pellets followed by ii) faster crystallization in the interior of the carriers pellet. The second stage proceeds faster giving 50–90 wt.% zeolite/SiO₂, leaving empty spaces inside the pellets and fully destroying the carriers pore structure. At low (<15 wt.%) and high (>50 wt.%) loadings, zeolite crystals are partially blocked with amorphous material. The optimal zeolite loading providing good accessibility of small crystals and maximal catalytic activity is about 40 wt.%.