Lignin based route to hydrocarbon fuels: catalytic hydrodeoxygenation of vanillin dimers hydrovanilloin and divanillin

The transformation of lignocellulosic biomass to sustainable fuels is a current research interest due to depletion of fossil resources and climate change concerns. In this work, catalytic hydrodeoxygenation of two lignin derived vanillin dimers hydrovanilloin and divanillin were studied to develop routes to C9-C14 range sustainable hydrocarbon fuel intermediates. Three bimetallic catalysts Ir-ReO x /SiO 2 , Ir-MnO x /SiO 2 , Re-MnO x /SiO 2 and Pd/C were tested for the hydrodeoxygenation of hydrovanilloin and divanillin under 6.9 MPa H 2 at 210 °C, 4 h. Ir-ReO x /SiO 2 catalyzed hydrodeoxygenation produced the highest proportion of C 14 H 26 hydrocarbons. Reduction of hydrovanilloin with Ir-ReO x /SiO 2 gave 1,2-ethanediyl-bis-cyclohexane as the major product in 52 % yield, whereas divanillin gave 3,3′-dimethyl-1,1′-bicyclohexane as the major product in 22 % yield. Ir-MnO x /SiO 2 and Re-MnO x /SiO 2 resulted fragmentation and separation of aromatic rings of hydrovanilloin and divanillin structures producing 2-methoxy phenol and 2-methoxy, 4-methyl phenol as major products. In addition, methoxy and phenol groups as well as aromatic rings were tolerated by Ir-MnO x /SiO 2 or Re-MnO x /SiO 2 catalysts. XPS of the catalysts shows the presence of IrO 2 and ReO 2 in these catalysts and synergistic effect of both IrO 2 and ReO 2 is crucial for the prevention of fragmentation during hydrodeoxygenation.