LiCoO2 impregnated nano-hierarchical ZSM-5 assisted catalytic upgrading of Kraft lignin-derived liquefaction bio-oil

Abstract

In this study, Kraft lignin-derived bio-oil was upgraded with LiCoO₂ or Co₃O₄-impregnated hierarchical nano-ZSM-5 catalysts. The synthesized catalysts were characterized by N₂-Ads-Des, XRD, XPS, NH₃-TPD, FTIR, FESEM and ICP-OES analyses. Upon incorporation of LiCoO₂ and Co₃O₄ onto the HZSM-5 support, the MFI structure of HZSM-5 remained intact. All the catalysts displayed a combination of Type-I and -IV isotherms. The upgraded bio-oil showed a significant increase in the amounts of alkylated guaiacols owing to the reduction in unsubstituted guaiacols, alkenyl guaiacols, and homovanillic acid. Hydrogenation, alkylation, and deoxygenation were the plausible bio-oil upgrading pathways. With the increase in cobalt content, weak acidity decreased through all the catalysts, while LiCoO₂ provided supplementary acid sites that increased the total acidity of LiCoO₂/HZSM-5 compared to the Co₃O₄/HZSM-5 catalyst. LiCoO₂/HZSM-5 with a low cobalt content (5% and 10% Co) displayed high selectivity for the production of alkylated guaiacols owing to their strong acidity. The upgraded bio-oils showed an increase in carbon and hydrogen followed by a decrease in oxygen content. The maximum higher heating value (∼29.83 MJ kg⁻¹) was obtained for the 10% Co (LiCoO₂)/HZSM-5 catalyst. In general, LiCoO₂/HZSM-5 outperformed the Co₃O₄/HZSM-5 catalyst. XRD of the spent 10% Co (LiCoO₂)/HZSM-5 suggested the complete loss of lithium from the catalyst with the retention of the MFI structure of the HZSM-5 support. In this study, it was successfully demonstrated that the main constituent of the cathode material of spent lithium-ion batteries i.e. LiCoO₂ could be employed to synthesize a novel and cheap catalyst for bio-oil upgrading while addressing the e-waste management issue in a sustainable manner.