Fig. 8. BJH pore size distributions of four ZSM-5 samples obtained by different operating processes.
Surface- and bulk- chemical compositions of ZSM-5 were measured by XPS and XRF respectively, which are displayed in Table 2. Both on surfaces and in bulk phases, the Si/Al ratios of ZSM-5 samples obtained via RPB premix are much lower than those via STR premix, which indicates that the concentration of Al sites is correlated with the micromixing intensity in the zeolite nucleation period. The significant increase in the Al content of ZSM-RS/RD indicates that enhancing micromixing by RPB premix plays a quite important role in the formation of Al sites in the zeolite in the growth process. Besides, the Al contents on surfaces of ZSM-5 samples are higher than those in bulk phases, which is correspond with the zeolite SAPO-34 reported by Xing et al. [44]. Moreover, with the same premixing process, the products prepared by dynamic crystallization could impel more Al into the bulk of zeolite ZSM-5 compared with those obtained by static crystallization, which indicates that intensifying micromixing by dynamic crystallization improves the driving force of substitution reaction of Al.
Table 2. Chemical composition of ZSM-5 samples analyzed by XRF and XPS.