Efficient and stable Fe-Ce-Al catalyst for catalytic deoxygenation of lignin for phenol and hydrocarbon-rich fuel: Effect of the synthesis method

To develop a structure-tailoring catalyst for catalytic conversion of lignin for value-added chemicals, a series of novel Fe-Ce-Al metal oxide catalysts was synthesized via different methods to tailor activity and structure for catalytic pyrolysis of lignin to enhance hydrocarbon-rich bio-oil. The results revealed that FeCeAl-CO catalysts derived from coprecipitation method with smaller particle sizes exhibited excellent catalytic deoxygenation activity due to higher Lewis/Brønsted acid, reversible Ce³⁺/Ce⁴⁺ redox pairs, tailorable oxygen vacancies and promoted β-O-4, aromatic-OCH₃ and side-chain cleavage. Additionally, coprecipitation method was facilitated to enhance hydrogen transfer, side-chain cleavage and aromatization reactions, while wet impregnation was beneficial to enhance demethoxylation and H-abstraction activity. During catalytic pyrolysis process, over 57.91% of hydrocarbon, including 20.21% and 25.71% for aromatics and olefins were achieved over FeCeAl-CO catalyst. Over 60.74% phenols and 52.48% alkylphenols were obtained over Fe-Ce/Al₂O₃-IM catalyst due to synergistic effect of FeOx and CeOx species. Fe-Ce-Al catalyst exhibited great activity and stability after fourth run, greater Brønsted acid-favored lignin cleavage and coke deposition, and metal active species leaching, oxidation and pore blockage were the key reasons for deactivation. Therefore, these findings could provide a cost-effective method for designing structure-tailoring catalysts for direct catalytic deoxygenation of lignin to generate hydrocarbon-rich upgrading bio-oil.