Catalytic hydrodeoxygenation and transfer hydrogenation of renewable ligninderived phenolics

Bio-oil obtained from biomass pyrolysis needs to be upgraded prior to its use as fuel since it contains high content of oxygenated compounds. Catalytic hydrodeoxygenation (HDO) is considered as an efficient technique for upgrading of pyrolysis bio-oil. The objective of this work was to study the HDO of phenolic compounds derived from lignin fraction of biomass since phenolics are highly stable in HDO reaction. Catalytic performance of Pd/C and Pt/C catalysts for HDO of renewable lignin-derived phenolic compounds (phenol, guaiacol and vanillin) and a simulated phenolic bio-oil was carried out at mild operating conditions of 275 °C and 16 bar hydrogen pressure. Pt/C showed to be more active than Pd/C for HDO of phenolic compounds. Meanwhile, physically mixed catalysts of HZSM-5 with Pt/C or Pd/C showed enhanced HDO efficiency compared to Pt/C and Pd/C due to promotion of reactions such as dehydration and hydrocracking over zeolite acid sites. Considering the difficult control of pressurized hydrogen gas in large industrial scale as well as high cost of molecular hydrogen production, it is of significant importance to find alternative sources of hydrogen. The feasibility of replacing hydrogen gas with liquid hydrogen donors was examined by transfer hydrogenation of the simulated phenolic bio-oil over Pt/C using decalin and tetralin as hydrogen source.