What is HZSM-5? I have seen it used as a catalyst support in literature. It seems to be related to the ZSM-5 zeolite, but I am not sure how.
According to this article(1), the difference between the zeolites HZSM-5 and ZSM-5 is that the first has a monoclinic and the second has an orthorhombic framework.
(1) H. van Koningsveld, J.C. Jansen, H. van Bekkum, The monoclinic framework structure of zeolite H-ZSM-5. Comparison with the orthorhombic framework of as-synthesized ZSM-5, Zeolites, Volume 10, Issue 4, 1990, Pages 235-242