Gd/HZSM-5 catalyst for conversion of methanol to hydrocarbons: Effects of amounts of the Gd loading and catalyst preparation method

- Gd changed physicochemical nature, selectivity, and stability of ZSM-5.
- Impregnation of Gd on ZSM-5 enhanced lifetime and olefin selectivity.
- Ion-exchanged Gd led to strong Lewis acidity and high aromatic selectivity.
- Formation of aromatic structured coke decreased by half on the Gd modified HZSM-5.

In this work, the effect of the gadolinium (Gd) content and preparation method on the characteristics of Gd-modified HZSM-5 catalysts and their reactivity in a methanol-to-hydrocarbons (MTH) reaction has been studied in detail. Gd/HZSM-5 catalysts with Gd contents of 1 wt% (1GdHZ), 5 wt% (5GdHZ), and 10 wt% (10GdHZ) were prepared by an incipient wet impregnation method, and another Gd-modified HZSM-5 catalyst (GdHZ_IE) was prepared by an ion exchange method. It was found that increasing the Gd content in the catalysts prepared via the impregnation method with uniformly distributed nano-sized particles and thin films of Gd2O3 directly influenced the crystallinity, surface area, pore volume, acid-base properties, and reactivity of the catalysts. In particular, the amount of Lewis acid sites (LAS) on the catalyst determine the selectivity of light olefins and aromatics during the MTH reaction. In contrast, the GdHZ_IE catalyst possess a larger number of strong LAS and show higher aromatic selectivities compared with the bare HZSM-5 catalyst. Regardless of the preparation method, the catalyst modification by Gd inhibited the formation of polycondensed aromatic species on the catalyst surface and reduced the amount of carbon deposition by more than 50%. As the increasing amounts of Gd reduced the amount of carbon deposition, the lifetimes of the Gd/HZSM-5 catalysts were also prolonged.

Scheme of a methanol-to-hydrocarbon reaction over the coke-tolerant Gd modified ZSM-5 catalyst and comparison of catalytic lifetime over HZSM-5 (solid black circle) and Gd/HZSM-5 (solid red square) for the reaction.202