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Lignin is a byproduct of the paper mill and second-generation (2G) ethanol biorefinery and the largest naturally available source of aromatic building blocks. It can serve as a feedstock to produce bulk, fine, and functionalized aromatic compounds along with aliphatic cyclic alcohols, jet fuel, and aliphatic hydrocarbons. Hydrodeoxygenation (HDO) is one of the promising strategies to produce these compounds from lignin-derived phenolics. Many reactions occur during the HDO; hence, it is very crucial to design active, selective, and long-life catalysts and choose the optimal reaction conditions to synthesize targeted end products. Herein, we first survey the conventional and new lignin fractionation techniques and determine the lignin structure, composition, and bonding with cellulose and hemicellulose. After this, we review the recent advances in the production of alkanes, arenes, cyclic alcohols, jet fuel range hydrocarbons, and HDO of raw lignin bio-oil. This review exclusively discusses the product distribution during HDO based on catalyst composition, solvent, and reaction parameters. Moreover, the review also underlines the selectivity of various catalytic systems to yield specific products such as BTX, important petrochemical materials, aliphatic hydrocarbons, cyclic alcohols, and jet fuel range hydrocarbons.

Despite considerable achievements in the hydrogenation of aromatic hydrocarbons over the past few years, the ability to hydrogenate arene or heteroarene rings in a highly selective manner in the presence of other reducible sites or without harming the remaining molecular structure has long been a major challenge. Such chemoselectivity and functional group tolerance is highly desirable for enabling direct access to key building blocks of polymers and pharmaceutical agents. For achieving such high selectivity, the development of suitable catalysts is of central importance. Herein, we report a convenient method for the scalable preparation of ruthenium oxide (RuO2) nanoparticles supported on pine needle char (PNC) by simple impregnation of ruthenium salt on unactivated PNC, a solid byproduct (biochar) obtained in the slow pyrolysis of biomass pine needles. The resulting RuO2-based nanocatalyst (RuO2@PNC) exhibited remarkable activity and high selectivity for the hydrogenation of more than 50 challenging arenes and heteroarenes, including biomass-derived aromatic compounds (e.g., 4-n-propylphenol, furfuryl alcohol, and 2-methyl furan). The synthetic value of this transformation is showcased for the hydrogenation of arene mixture present in petroleum refineries or coal tars as well as biomass-derived oils (bio-oils) with enriched furfural, ether, and phenol derivatives. Under optimized conditions, the performance of this new catalyst was compared with state-of-the-art commercial catalysts such as Ru/C, Pd/C, and Raney nickel and found that RuO2@PNC is more superior and selective. Furthermore, the catalyst is easily recovered and reused up to four cycles.