| Abstract: | In this work the acid properties of a series of HZSM-12 zeolites with different Si/Al ratio were studied. The ZSM-12 crystals were synthesized by the hydrothermal method starting from a gel with the following molar composition: 20MTEA:10Na2O:x Al2O3:100SiO2:2000H2O, with x = 0.50, 0.67, 1, 1.25 and 2, respectively. The gels were crystallized at 140∘C for 6 days, then washed, dried and calcined to remove the MTEA template. The samples were ion-exchanged with an ammonium chloride solution and calcined again to obtain the zeolites in the acid form. The materials thus obtained were characterized by XRD, SEM, BET, TG and n-butylamine adsorption. The Si/Al ratio in the reaction mixture affects the amount of zeolite produced and the size of the particles. The XRD analysis indicated that the ZSM-12 zeolite crystallizes in a pure form only with Si/Al ratio above 33. The SEM analysis showed the presence of crystallites with very well defined prismatic shapes. The removal of the MTEA of the pores of the ZSM-12 by TG indicated that there are two kinds of internal sites occupied by MTEA inside the structure. The BET area of the ZSM-12 decreases proportionally with the crystallinity of materials. The desorption of n-butylamine showed that the acid site density is proportional to aluminum content, but the Si/Al ratio shows little influence on the relative strengths of these sites. |
