Hydrodeoxygenation of Biomass-derived Oxygenate Mixtures Over Pt/C and HZSM-5 Mixed Catalysts

Bifunctional catalysts consisting of metal and acid sites are generally used for transformation of bio-oil/bio-oil model compounds via hydrodeoxygenation (HDO). Active metal sites are important for hydrogenation and demethoxylation reactions, while the acid sites are required for dehydration and alkylation reactions during HDO. Platinum group metals have demonstrated high HDO activity owing to their excellent hydrogenation character. In the present work, the HDO activities of Pt, Pd and Ru-supported activated carbon (AC) are evaluated for HDO of isoeugenol and binary mixtures of isoeugenol with acetic acid and furfural. Pt/AC showed superior HDO activity compared to other catalysts owing to the presence of metallic Pt-0 over AC, while Pd and Ru were observed in both metallic and oxide states (Pd+ 2 and Ru+ 4). The selectivity to propyl cyclohexane (PC) enhanced as temperature increased from 240 to 280 degrees C over all the three catalysts. Further, the HDO of isoeugenol was investigated over physically mixed Pt/AC and HZSM-5 catalysts. An improved selectivity towards PC was observed over the mixed catalyst (57.1%) as compared to that over Pt/AC (36.9%), due to the presence of acid sites offered by HZSM-5. Noticeably, superior HDO activity was observed at shorter reaction time over mixed catalysts (60 min) compared to Pt/AC (120 min). While the HDO of single model compounds has been studied extensively, the effect of multiple oxygenate groups on catalytic activity is scarcely explored in the literature. Therefore, the activities of Pt/AC and mixed catalysts were evaluated for the HDO of binary blends of isoeugenol with acetic acid and furfural. Both acetic acid and furfural inhibited the HDO of isoeugenol. The presence of furfural drastically reduced the deoxygenation activity of both the catalysts. The yield of PC decreased drastically from 25.5 to 0.6% when treated with furfural over Pt/AC, and from 35.5 to 1.2% over physically mixed catalysts. The use of mixed catalyst, however, reduced the inhibiting effect of acetic acid on the HDO of isoeugenol.