Abstract

Understanding the influence of pyrolysis oil components on the activity, selectivity and deactivation of nickel-based catalysts during hydrodeoxygenation (HDO) is fundamental to optimise the process for long-term operation and to develop new catalyst formulations. In this study, HDO of a bio-oil light phase and an aqueous solution of phenol (as a model compound) were investigated over fresh and regenerated NiCu/Al2O3 in a batch reactor at 250 and 340 °C. The produced upgraded oil over the fresh catalyst contained significant quantities of ketones and phenolic compounds, which were not further converted during hydrotreatment. In the bio-oil environment, the regenerated catalyst showed only marginally lower activity (15% less H2 consumption) in comparison to the fresh one. In contrast, phenol in water was completely converted over fresh NiCu/Al2O3 with high selectivity towards cyclohexanol at 250 °C and cyclohexane at 340 °C. Once exposed to bio-oil the catalyst no longer showed activity towards phenol conversion in water. Characterization of the spent catalysts indicated the formation of Ni3S2 in addition to coke and alkali metal deposition on the catalyst surface. Other nickel-based catalysts (with different supports and loadings) and two bio-oils with varying sulphur concentration and no minerals were also investigated. Overall the results elucidated that the catalyst activity, selectivity and deactivation of certain reaction paths was mainly determined by the presence of sulphur. By limiting the effects of sulphur poisoning, Ni-catalysts may be considered for the production of fine chemicals, such as ketones and phenols, in addition to fuel synthesis.