Influence of H<sub>2</sub>O and H<sub>2</sub>S on the composition, activity, and stability of sulfided Mo, CoMo, and NiMo supported on MgAl<sub>2</sub>O<sub>4</sub> for hydrodeoxygenation of ethylene glycol [electronic resource]

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Tác giả:

Ngôn ngữ: eng

Ký hiệu phân loại: 660.6 Biotechnology

Thông tin xuất bản: Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2017

Mô tả vật lý: Size: p. 106-121 : , digital, PDF file.

Bộ sưu tập: Metadata

ID: 263107

 Here in this work, density functional theory (DFT), catalytic activity tests, and in-situ X-ray absorption spectroscopy (XAS) was performed to gain detailed insights into the activity and stability of MoS<
 sub>
 2<
 /sub>
 , Ni-MoS<
 sub>
 2<
 /sub>
 , and Co-MoS<
 sub>
 2<
 /sub>
  catalysts used for hydrodeoxygenation (HDO) of ethylene glycol upon variation of the partial pressures of H<
 sub>
 2<
 /sub>
 O and H<
 sub>
 2<
 /sub>
 S. The results show high water tolerance of the catalysts and highlight the importance of promotion and H<
 sub>
 2<
 /sub>
 S level during HDO. DFT calculations unraveled that the active edge of MoS<
 sub>
 2<
 /sub>
  could be stabilized against SO exchanges by increasing the partial pressure of H<
 sub>
 2<
 /sub>
 S or by promotion with either Ni or Co. The Mo, NiMo, and CoMo catalysts of the present study were all active and fairly selective for ethylene glycol HDO at 400 �C, 27 bar H<
 sub>
 2<
 /sub>
 , and 550?2200 ppm H<
 sub>
 2<
 /sub>
 S, and conversions of ?50?100%. The unpromoted Mo/MgAl<
 sub>
 2<
 /sub>
 O<
 sub>
 4<
 /sub>
  catalyst had a lower stability and activity per gram catalyst than the promoted analogues. The NiMo and CoMo catalysts produced ethane, ethylene, and C1 cracking products with a C<
 sub>
 2<
 /sub>
 /C<
 sub>
 1<
 /sub>
  ratio of 1.5?2.0 at 550 ppm H<
 sub>
 2<
 /sub>
 S. This ratio of HDO to cracking could be increased to ?2 at 2200 ppm H<
 sub>
 2<
 /sub>
 S which also stabilized the activity. Removing H<
 sub>
 2<
 /sub>
 S from the feed caused severe catalyst deactivation. Both DFT and catalytic activity tests indicated that increasing the H<
 sub>
 2<
 /sub>
 S concentration increased the concentration of SH groups on the catalyst, which correspondingly activated and stabilized the catalytic HDO performance. In-situ XAS further supported that the catalysts were tolerant towards water when exposed to increasing water concentration with H2O/H2S ratios up to 300 at 400?450 �C. Raman spectroscopy and XAS showed that MoS2 was present in the prepared catalysts as small and highly dispersed particles, probably owing to a strong interaction with the support. Linear combination fitting (LCF) analysis of the X-ray absorption near edge structure (XANES) spectra obtained during in-situ sulfidation showed that Ni was sulfided faster than Mo and CoMo, and that Mo was sulfided faster when promoted with Ni. Extended X-ray absorption fine structure (EXAFS) results showed the presence of MoS<
 sub>
 2<
 /sub>
  in all sulfided catalysts. Lastly, sulfided CoMo was present as a mixture of CoMoS and Co<
 sub>
 9<
 /sub>
 S<
 sub>
 8<
 /sub>
 , whereas sulfided NiMo was present as NiMoS.
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