Catalytic deoxygenation of carboxyl compounds in the hydrothermal liquefaction crude bio-oil via in-situ hydrogen supply by CuO-CeO2/γ-Al2O3 catalyst

Hydrothermal liquefaction (HTL) has drawn great attention as a potential method to produce bio-oil from biomass waste. However, bio-crude from HTL shows undesired high-oxygen content and needs further deoxygenation upgrading. Herein, stearic acids as a model carboxylic compounds in HTL bio-crude was employed to investigate catalytic deoxygenation performance. Results showed that (CuO)(10)-CeO2/gamma-Al2O3 had the most superior catalytic deoxygenation performance for the stearic acids. The maximum stearic acid conversion rate (96.36%) and total hydrocarbon yield (88.79%) were obtained at 300 degrees C, 12 h, ratio of stearic acid to water 1 : 4. The main catalytic deoxygenation pathways were proposed: carbon monoxide generation (decarbonylation) - in-situ hydrogen generation (water-gas shift) - short-chain fatty acid generation (hydrogenolysis) - n-alkanes generation (decarboxylation, hydrodeoxygenation and hydrogenation). DFT calculation elucidated that CuO-CeO2 reduced the activation energy from 24.8 kcal mol(-1) (vacuum) to 15.0 kcal mol(-1) (catalytic). Thus, deoxygenation via CuO-CeO2/gamma-Al2O3 would be an effective method for upgrading HTL bio-crude.

Automated summary

Hydrothermal liquefaction (HTL) has the potential to produce bio-oil from biomass waste, but further deoxygenation is needed due to the high oxygen content. This study investigated the catalytic deoxygenation performance of stearic acids in HTL bio-crude and found that (CuO)(10)-CeO2/gamma-Al2O3 exhibited the best performance. The proposed catalytic deoxygenation pathways involved carbon monoxide generation, in-situ hydrogen generation, short-chain fatty acid generation, and n-alkanes generation. DFT calculation showed that CuO-CeO2 reduced the activation energy, making it an effective method for upgrading HTL bio-crude.