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/γ-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°C, 12h, 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 24.8kcalmol⁻¹ (vacuum) to 15.0kcalmol⁻¹ (catalytic). Thus, deoxygenation via CuO-CeO2/γ-Al2O3 would be an effective method for upgrading HTL bio-crude.