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.