On methanol to hydrocarbons reactions in a hierarchically structured ZSM-5 zeolite catalyst

• Published in: Catalysis today Vol. 303; pp. 150 - 158
• Main Authors: Kim, Heejoong, Jang, Hoi-Gu, Jang, Eunhee, Park, Sung Jun, Lee, Taehee, Jeong, Yanghwan, Baik, Hionsuck, Cho, Sung June, Choi, Jungkyu
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.04.2018
• Subjects: Acid site titration; Hierarchically structured ZSM-5; Methanol-to-hydrocarbons reaction; Propene/ethene ratio; Self-pillared ZSM-5; Acid site titration; Self-pillared ZSM-5; Hierarchically structured ZSM-5; Propene/ethene ratio; Methanol-to-hydrocarbons reaction
• ISSN: 0920-5861; 1873-4308
• DOI: 10.1016/j.cattod.2017.09.032

[Display omitted] •Hierarchically structured ZSM-5 catalysts were synthesized via self-pillaring.•Mesopores in the range of 2–10nm were formed due to the space among the pillars.•The self-pillared ZSM-5 was used for methanol to hydrocarbons (MTH) reactions.•Reduced diffusion length in a catalyst allowed for a selective production of propene.•The propene/ethene ratio as high as 9.1 from the MTH reaction was achieved. Two type ZSM-5 catalysts (Si/Al ratio of ∼30) with different mesoporosity were synthesized by using a structure directing agent of tetra-n-butylphosphonium hydroxide. In particular, the molar compositions of ethanol and water in the synthetic precursor were changed in order to acquire the two type ZSM-5 catalysts. The resulting ZSM-5 catalysts were formed via the interconnection of very thin pillars or lamellae; (1) ∼6nm thick with marked mesoporosity (H_30; high mesoporous ZSM-5) and (2) ∼13nm thick without any considerable mesoporosity (L_30; low mesoporous ZSM-5). The pyridine-based acid titration reveals that H_30 had internal Brønsted acid sites similar to those in the commercially available ZSM-5 with a Si/Al ratio of 75 (referred to as C_75), though H_30 contained a large amount of external Brønsted acid sites. The methanol to hydrocarbons (MTH) reaction performance of these two ZSM-5 catalysts demonstrates that H_30 preferred to produce propene over ethene compared to C_75, while L_30 showed a very poor MTH performance mainly due to the lower amount of internal Brønsted acid sites. More desirably, a very short diffusional length (∼18,600 times lower than that in C_75) in H_30 considerably disfavored the aromatic dealkylation that is known to produce ethene. With this, H_30 allowed for achieving the ratio of propene to ethene as high as ∼9.1, which is, to the best of our knowledge, a highest value among the MTH results on ZSM-5 catalysts without any co-feed. Furthermore, ceria-doped H_30 not only enhanced the stability for the MTH reaction via a passivation of the external Brønsted acid sites, but also improved a propene to ethene ratio up to ∼15.0.