(544ey) Enhancement of Mo/ZSM-5 Catalysts in Methane Aromatization By Addition of Fe Promoters and By Reduction/Carburization Pretreatment

Upgrade of natural gas to value-added aromatic compounds in an efficient way is of great importance in the chemicals industry. In 1993, Wang et al. [1] laid the groundwork on non-oxidative methane aromatization, which converts methane to aromatic compounds, mainly benzene, using MoOx supported on ZSM-5 as catalyst. Since then, many research groups have taken a keen interest in methane aromatization. However, the use of Mo/ZSM-5 catalyst at an industrial level is hindered by its rapid deactivation due to formation of carbon deposits.

Our work involves investigating ways to impede deactivation by carbonaceous deposits by studying the effects of doping Mo/ZSM5 catalyst with Fe and employing different catalyst pretreatment methods.

In the current work we explore the catalytic behavior of catalysts consisting of 6 wt% Mo/ZSM-5 with 0, 0.2 and 1wt% Fe tested with two types of pretreatment: 1) heating under He flow, 2) reducing in H₂/CH₄ and carburizing in CH₄. Under He pretreatment, adding 0.2 wt% Fe improved the benzene yield, but 1 % Fe slightly decreased it. Precarburizing the catalysts resulted in enhanced catalytic properties for all Fe loadings, and furthermore, improved the catalyst stability. The precarburized 6wt% Mo-0.2wt%Fe catalyst presented the highest benzene yield (6.9%), which was almost stable in the subsequent 10-hour test. The fresh and spent catalysts were characterized by XRD, N₂ adsorption, TPR, SEM, TPO and TGA. The results show that precarburized catalysts are more stable due to the formation of smaller amounts of carbon deposits, and consequently lower pore blockage. Addition of Fe causes the carbon deposits to be more reactive and easier to burn off. Higher Fe loadings are linked to the formation of carbon nanotubes.

[1] Wang, L.; Tao, L.; Xie, M. et al. Catal. Lett. 21 (1993), 35-41