Investigating the effect of Fe as a poison for catalytic HDO over sulfided NiMo alumina catalysts

The effect of iron (Fe) as poison present in renewable feeds was studied during hydrodeoxygenation (HDO) over molybdenum based sulfided catalysts. The study was carried out at 6 MPa and 325 degrees C in batch reaction conditions. Different concentrations of Fe in the feed were tested over MoS2/Al2O3 and NiMoS/Al2O3. A notable drop in activity for the conversion of oxygenates was observed for both catalyst systems with an increased concentration of Fe in the feed. However, the changes in selectivity of products was opposite for unpromoted and Ni-promoted catalysts. In the case of the NiMoS catalyst, at higher Fe concentration, the decarbonated product (C-17 hydrocarbons) decreased while the direct hydrodeoxygenation product (C-18 hydrocarbons) increased. On the contrary, for the base catalyst (MoS2), there was a decrease in the yield of direct hydrodeoxygenation (C-18 hydrocarbons) products and an increase in yield of decarbonated products (C-17 hydrocarbons). These sulfided catalysts have different sites for these two different reaction routes and they interacted differently with Fe during the deactivation process. With surface deposition of Fe, the ability of these catalysts to create active sites i.e. via sulfur vacancies deteriorated. TEM-EDX results suggested that the effect of Ni as a promoter for the decarbonation route was nullified and a resultant FeMo phase explains the drop in activity and change in selectivity.