Influence of H2O and H2S on the Composition, Activity, and Stability of Sulfided Mo, CoMo, and NiMo Supported on MgAl2O4 for Hydrodeoxygenation of Ethylene Glycol

Abstract 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 2 , Ni-MoS 2 , and Co-MoS 2 catalysts used for hydrodeoxygenation (HDO) of ethylene glycol upon variation of the partial pressures of H 2 O and H 2 S. The results show high water tolerance of the catalysts and highlight the importance of promotion and H 2 S level during HDO. DFT calculations unraveled that the active edge of MoS 2 could be stabilized against S O exchanges by increasing the partial pressure of H 2 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 2 , and 550–2200 ppm H 2 S, and conversions of ≈50–100%. The unpromoted Mo/MgAl 2 O 4 catalyst had a lower stability and activity per gram catalyst than the promoted analogues. The NiMo and CoMo catalysts produced ethane, ethylene, and C 1 cracking products with a C 2 /C 1 ratio of 1.5–2.0 at 550 ppm H 2 S. This ratio of HDO to cracking could be increased to ≈2 at 2200 ppm H 2 S which also stabilized the activity. Removing H 2 S from the feed caused severe catalyst deactivation. Both DFT and catalytic activity tests indicated that increasing the H 2 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 H 2 O/H 2 S ratios up to 300 at 400–450 °C. Raman spectroscopy and XAS showed that MoS 2 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 2 in all sulfided catalysts. Sulfided CoMo was present as a mixture of CoMoS and Co 9 S 8 , whereas sulfided NiMo was present as NiMoS.