Direct synthesis of c-axis-oriented HZSM-5 zeolites in polyacrylamide hydrogel

c-Axis-oriented HZSM-5 zeolites were directly synthesized by introducing crosslinked polyacrylamide (C-PAM) hydrogels into ZSM-5 synthesis gels. The growth orientation of the crystals as well as the acidity of ZSM-5 could be modulated by the C-PAM content in the synthesis gel. The crystal growth along the a-axis and b-axis was obviously restricted, whereas c-axis growth was distinctly promoted with increasing C-PAM content, which was probably due to the C-PAM having stronger interactions with the {010} and {100} facets than the {101} facet. Sample Z-2, which was prepared with 2% C-PAM exhibited the shortest b-axis length elongated prism structure and strong acid sites. Furthermore, Z-2 exhibited excellent catalytic performance in the methanol-to-olefin (MTO) reaction showing the highest methanol conversion (100%) and the light olefin selectivity (TOS) (81.2%), as well as the longest lifetime (>23 h).