(125b) Hydrodeoxygenation of Biomass-Derived Compounds to Biofuels

Due to the depletion of fossil fuels and environmental concerns, exploring green and renewable routes with commercial viability for the increased demand of energy and chemicals has become one of the most urgent challenges.  As a naturally abundant resource, biomass has been recognized as one of the potential alternatives to produce biofuels ^[1]. In this work, guaiacol was used as model compound, carbon supported metal catalysts (Cu/C, Fe/C, Pd/C, Pt/C, PdFe/C and Ru/C) have been prepared, characterized and tested for vapor-phase hydrodeoxygenation (HDO) of guaiacol (GUA) at atmospheric pressure (Table 1). Phenol was the major intermediate on all catalysts. Over the noble metal catalysts saturation of the aromatic ring was the major pathway observed at low temperature (250 °C), forming predominantly cyclohexanone and cyclohexanol. Substantial ring opening reaction was observed on Pt/C and Ru/C at higher reaction temperatures (e.g., 350 °C). Base metal catalysts, especially Fe/C, were found to exhibit high HDO activity without ring-saturation or ring-opening with the main products being benzene, phenol along with small amounts of cresol, toluene and trimethylbenzene (TMB). Interestingly, a substantial enhancement in HDO activity was observed on the PdFe/C catalysts. Compared with Fe/C, the yield to oxygen-free aromatic products (i.e., benzene/toluene/TMB) on PdFe/C increased by a factor of four at 350 °C, and by approximately a factor of two (83.2% versus 43.3%) at 450 °C. The enhanced activity of PdFe/C is attributed to the formation of PdFe alloy as evidenced by STEM, EDS and TPR.                 

Table 1: Catalytic performance for HDO of guaiacol.^a

^*Represent products yield. ^a Reaction conditions: 100 mg, P_guaiacol=0.42 %; P_H2=40%; W/F=0.15 s.g.mL^-1; ^bGas phase products mainly include methanol,  methane, CO, CO₂ and small amounts of ethane. ^c others represent unidentified species which was quantified based on the catechol, for 2Pd10Fe/C, others refers to biphenyl; For 5Ru/C and 5Pt/C, others are mainly composed of other hydrogenated six-membered ring compounds (e.g., 2-methoxycyclohexanone, 2-methoxycyclohexanol) and traces amount of anisole, 1,2-dimethoxyphenol. Note: Theoretically, when gas phase selectivity is lower than 14.2% (corresponding to 1mol gas products per GUA via demethylation/demethoxylation), we assume there is negligible ring-opening reaction.

1. G.W. Huber, S. Iborra, A. Corma, Chem. Rev. 2006, 106, 4044.