(491d) Synthesis and Characterization of Mesoporous Zsm-12 by Using Carbon Particles

The generation of
mesoporosity in 1-dimensional zeolite ZSM-12 was explored by using carbon black
as template during synthesis. After the carbon particles were burned off,
intracrystalline mesopore networks were formed. Mesoporous ZSM-12s with nominal
Si/Al ratios of 40, 60, 75, 100 in the gel, were successfully synthesized. For
relatively high C/Si and H₂O/Si ratios, there is higher chance to
generate mesoporosity. Mesopore volumes around 0.15-0.19 cm³/g and mesopores distributed in the range of 10-50 nm were
determined by nitrogen physisorption. The STPD and FT-IR results revealed that
these mesoporous ZSM-12s have the same number of acid sites as regularly
synthesized ZSM-12s for comparable Si/Al ratios. For
the synthesis gel containing the same nominal Si/Al ratios, the Si/Al ratios of
the generated zeolites were almost the same in both the mesoporous and conventional
ZSM-12 products, which indicated that the carbon black involved in the
synthesis did not affect the crystallization efficiency of aluminum during the
nucleation. The conversion of n-tridecane and 1,3-dimethylcyclyhexane
were chosen as test reactions. The mesoporous ZSM-12s are found to exhibit
higher activity compared to conventional ones especially under high WHSV. The
enhanced activity is attributed to the introduction of the mesopores in the
zeolite crystals, which decreases the intracrystalline mass transfer
limitations. Moreover, the mesoporous samples promoted the production of longer
and more branched products than the case of the traditional samples since the
former ones favor to a higher extent the outwards diffusion of the products. It
can be concluded that this is a general method for formation of mesoporosity
for zeolites materials, which leads to superior intracrystalline mass transfer
properties.