Role of metal support during ru-catalysed hydrodeoxygenation of biocrude oil

Abstract Hydrodeoxygenation (HDO) of guaiacol (a lignin-derived species) and biocrude oil was studied in a batch-type reactor operating at 4.0 MPa hydrogen over a series of Ru-based catalysts. Ru/BEA and Ru/ZSM-5, with varying Si/Al ratios, were investigated to examine the effect of pore size and acidity of supports on HDO of guaiacol and biocrude oil. In addition to this, large pore Ru/Al2O3 (possessing weak acid sites, 9.2 nm) and Ru/SiO2 (absence of acid sites, 15.2 nm) were also prepared and examined. It was observed that a decrease in the Si/Al ratio of the support results in an increase in the yield of cyclohexane and a decrease in the yield of 2-methoxycyclohexanol in HDO of guaiacol. This data also discloses the influence of the concentration of acid sites on the deoxygenation of 2-methoxycyclohexanol. Both Ru/BEA and Ru/ZSM-5, with both possessing low Si/Al ratios, display a high activity for HDO for guaiacol, while only the Ru/BEA catalyst exhibits a high activity for HDO of biocrude oil. Catalyst characterisation (BET, NH3-TPD and NH3 and acetonitrile-d3-FTIR) shows that the Ru/BEA catalyst, with a low Si/Al ratio, not only possesses strong Bronsted acid sites but also contains extensive mesoporosity. Notably, these mesopores appear to facilitate the hydrogenation, deoxygenation, and ring-opening of large oxygenated and condensed-ring hydrocarbons in biocrude oil which then leads to a high yield of cycloalkanes. As expected, the Ru/Al2O3 and Ru/SiO2 catalysts exhibit a high hydrogenation activity but a lower deoxygenation activity in the HDO of guaiacol and biocrude oil. These results suggest that the larger pore support, with strong Bronsted acid sites, engendered the HDO activity observed. The reaction pathway for the main components of biocrude oil was proposed based on the observed reaction product distribution.