Hollow ZSM-5 zeolite grass ball catalyst in methane dehydroaromatization: One-step synthesis and the exceptional catalytic performance

Abstract

One-step hydrothermal preparation method of hollow ZSM-5 zeolite grass ball (HGB-ZSM-5) was developed at the near-neutral circumstance. The electrostatic assembly among EDTA2−, n-butylamine+ and aluminosilicate species led to the self-transformation of irregular amorphous precursor into “Organic-Inorganic hybird ball” ([(SiO)4Al)−]m(C4H12N+)x(EDTA2−)y(C4H12N+)z[(SiO)4Al)−]n), which directly crystallized into hollow ZSM-5 zeolite grass ball. After the loading of Mo species, the catalytic performance of Mo/HGB-HZSM-5 catalyst was tested in MDA process. Compared with conventional Mo/ZSM-5 catalyst, Mo/HGB-HZSM-5 catalyst exhibited higher CH4 conversion and aromatic selectivity, as well as longer lifetime, which was attributed to the hollow assembly mode. Hollow grass ball structure not only improved the synergistic effect by promoting the formation of more Mo-acid sites and their uniformly distribution, but also increased the contact time as the unreacted CH4 and primary products diffused outward from the inside cavity through Mo/HZSM-5 shell, giving rise to the exceptional catalytic performance. Furthermore, this unique structure bestowed Mo/HGB-HZSM-5 with the smaller bulky density and the reduce of the sites concerned with the catalyst deactivation, which inhibited the side reactions and strengthened molecules diffusion, showing the higher catalytic stability.