Catalytic hydrocracking of pyrolytic lignin over bimetallic Ru-M/HZSM-5 (M = Ni, Fe or Co) for aromatic hydrocarbon production

Pyrolytic lignin (PL) can be converted into aromatic hydrocarbons through catalytic hydrocracking. This study investigated the performance of bimetallic Ru-M/HZSM-5 catalysts (M = Ni, Fe, or Co) in the hydrocracking of PL, focusing on the impact of introducing a second metal on the efficiencies of hydrodepolymerization (HDP) and hydrodeoxygenation (HDO). The 2Ru-5Ni/HZSM-5 catalyst exhibited the best performance in HDP and HDO. The introduction of Ni enabled the formation of RuNi alloy and additional metallic Ni sites for H₂ activation to enhance HDP. Furthermore, the RuNi alloy was proposed to promote the HDO of monophenols via a short-path hydrogen spillover between Ru and Ni, which was more efficient than HDO mediated by co-working of Ru and acid sites on unmodified Ru/HZSM-5. While RuFe and RuCo alloys could also strengthen HDO of monophenols through the aforementioned mechanism, the reduction of strong Brønsted acid sites by the incorporation of Fe or Co adversely impacted HDP. Under the optimum reaction conditions, the oil phase yield from hydrocracking over 2Ru-5Ni/HZSM-5 reached 51.42 %, with GC-detectable products accounting for approximately 78 %. Particularly, the yields of mono-ring and double-ring aromatic hydrocarbons were 21.08 % and 8.66 %, respectively. In addition, this catalyst demonstrated excellent reusability.