Synthesis of ZSM-5 Type Zeolites using 1 -Butanol and their Properties

Abstract

Synthesis of ZSM-5 type zeolites has been carried out using various structure-directing reagents such as amine, diamine, amino alcohol, hydrocarbon and alcohol as well as tetrapropylammonium bromide (TPABr). The role of the directing reagent and the properties of zeolites synthesized, however, have not been sufficiently clarified. In this paper, synthesis of ZSM-5 type zeolites was conducted using various aliphatic alcohol and their properties were investigated in detail. It was found that the highly crystalline ZSM-5 type zeolites were synthesized using 1-butanol and 1-hexanol (Table 1). In the case of 1-butanol, the crystallinity of zeolite was increased with an increase in 1-butanol/SiO₂ ratio of the starting synthesis mixture and the highest crystallinity was obtained for over 1 of 1-butanol/SiO₂ ratio (Table 2). The production of cristobalite as by-product was considerably depressed by addition of 1-butanol. These results indicate that 1-butanol acts as the structure-directing reagent. The SiO₂/Al₂O₃ ratios of zeolites synthesized using 1-butanol were lower than those of the starting synthesis mixtures. The region of SiO₂/Al₂O₃ ratio (30-150) was much smaller than that of zeolites with TPABr (Table 3). The Al-free zeolite, silicalite, could not be prepared using 1-butanol. Figure 4shows the FT-IR spectra of hydroxyl groups of HZSM-5 zeolites synthesized using (A) 1-butanol and (B) TPABr. The spectra of HZSM-5 from TPABr were characterized by two well-defined absorptions at 3605 and 3740 cm^-1. The former band has been assigned to stretching vibration of an acidic bridged OH of Si (OH) Al, while the latter one to terminal Si-OH. On the other hand, two peaks at 3605 and 3740 cm^-1 were also observed in the spectra of zeolites using 1-butanol. However, the intensity of the peak at 3740 cm^-1 was very weak. The drastic decrease in the intensity of the peak at 3740 cm^-1 may suggest the concentration of the internal Si-OH groups (structure defects) is relatively small. This is also confirmed by the fact that the amount of water adsorbed on zeolite synthesized with 1-butanol was smaller than that on zeolite with TPABr.