Tuning the Activity of NbOPO 4 with NiO for the Selective Conversion of Cyclohexanone as a Model Intermediate of Lignin Pyrolysis Bio-Oils

Catalytic upgrading of pyrolysis oils is an important step for producing replacement hydrocarbon-rich liquid biofuels from biomass and can help to advance pyrolysis technology. Catalysts play a pivotal role in influencing the selectivity of chemical reactions leading to the formation of main compounds in the final upgraded liquid products. The present work involved a systematic study of solvent-free catalytic reactions of cyclohexanone in the presence of hydrogen gas at 160 °C for 3 h in a batch reactor. Cyclohexanone can be produced from biomass through the selective hydrogenation of lignin-derived phenolics. Three types of catalysts comprising undoped NbOPO 4 , 10 wt% NiO/NbOPO 4 , and 30 wt% NiO/NbOPO 4 were studied. Undoped NbOPO 4 promoted both aldol condensation and the dehydration of cyclohexanol, producing fused ring aromatic hydrocarbons and hard char. With 30 wt% NiO/NbOPO 4 , extensive competitive hydrogenation of cyclohexanone to cyclohexanol was observed, along with the formation of C 6 cyclic hydrocarbons. When compared to NbOPO 4 and 30 wt% NiO/NbOPO 4 , the use of 10 wt% NiO/NbOPO 4 produced superior selectivity towards bi-cycloalkanones (i.e., C 12 ) at cyclohexanone conversion of 66.8 ± 1.82%. Overall, the 10 wt% NiO/NbOPO 4 catalyst exhibited the best performance towards the production of precursor compounds that can be further hydrodeoxygenated into energy-dense aviation fuel hydrocarbons. Hence, the presence and loading of NiO was able to tune the activity and selectivity of NbOPO 4 , thereby influencing the final products obtained from the same cyclohexanone feedstock. This study underscores the potential of lignin-derived pyrolysis oils as important renewable feedstocks for producing replacement hydrocarbon solvents or feedstocks and high-density sustainable liquid hydrocarbon fuels via sequential and selective catalytic upgrading.