545373 High and Stable Activity of Dealuminated Zn/H-ZSM-5 for Ethane Dehydroaromatization

Wednesday, June 5, 2019: 2:45 PM
Texas Ballroom EF (Grand Hyatt San Antonio)
Hikaru Saito1, Satoshi Inagaki2, Qian Han2, Ryota Terunuma1, Tomohiro Yabe1, Shuhei Ogo1, Yoshihiro Kubota2 and Yasushi Sekine1, (1)Applied Chem., Waseda Univ., Tokyo, Japan, (2)Yokohama National Univ., Yokohama, Japan

We investigated effects of steam treatment on Zn/H-ZSM-5 for ethane dehydroaromatization to suppress coke formation, which deactivates the activity. Steam treatment is a well-known technique to decrease the amount of Brønsted acid sites through converting framework Al species to extra framework ones.
Steam treatment of Zn/H-ZSM-5 prepared by an ion-exchange method was conducted in a fixed bed reactor at 823 K for 1 h under H2O/Ar flow. The steam-treated samples is denoted as Zn/H-ZSM-5 ST. Catalytic activity tests were conducted in a fixed bed reactor at 873 K and atmospheric pressure under 80vol% ethane and balanced nitrogen.
The initial activity of Zn/H-ZSM-5 ST was comparable to Zn/H-ZSM-5: ethane conversion is about 20%. Although the activity of Zn/H-ZSM-5 was rapidly deactivated in 2 h with time on stream, that of Zn/H-ZSM-5 ST was quite stable for 4 h. Temperature programmed oxidation revealed that the amount of carbon deposition on Zn/H-ZSM-5 ST is one-tenth smaller than that of Zn/H-ZSM-5. During steam treatment, the qualitative and quantitative nature of Zn was not changed from the results of UV-Vis DRS, XRD and ICP-OES. Therefore, we concluded that steam treatment affected Brønsted acidity. Then, we measured 29Si MAS NMR spectra to obtain information on the local structure of H-ZSM-5 supports. In the spectrum of steam-treated H-ZSM-5, the peak intensity of Q4(1Al), which means (AlO)Si(SiO)3, significantly decreased in comparison with parent H-ZSM-5. On the other hand, a little decrease in the peak intensity was observed in the spectrum of Zn/H-ZSM-5 ST. This indicates that ion-exchange of Zn2+ with H+ stabilize framework Al species. In other words, framework Al species related to H+ (Brønsted acid sites) would be easily converted to extra framework ones. Therefore, the suppression of coke formation was achieved thanks to the optimal amount of Brønsted acid sites.

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