Catalytic Hydrodeoxygenation of Lignin-Derived Oxygenates: Catalysis, Mechanism, and Effect of Process Conditions

Abstract

The high oxygen content of pyrolysis bio-oil with many organic functional groups in it limits its direct application as a blendstock. The upgradation of biomass-derived oxygenates into renewable fuels and value-added chemicals via catalytic hydrodeoxygenation (HDO) has received considerable attention in recent years. This review focuses on HDO of key model compound oxygenates, which sets the ground to propose the overall reaction mechanism of HDO of bio-oils. Catalysts play a vital role in HDO, and its design poses many challenges because of different reactions involved such as hydrogenolysis, hydrogenation, decarbonylation, and dehydration occurring simultaneously at different catalyst-active sites. The main objective here is to present a comprehensive introduction to the reaction mechanism involved in the HDO of bio-oil model oxygenates. For this, a thorough discussion of different reaction pathways taking place during the HDO of five model oxygenates, viz., anisole, guaiacol, eugenol, vanillin, and dibenzofuran, is presented. The model compounds are selected to provide a good description of the HDO of lignin-derived compounds present in bio-oils. Particular emphasis is placed on the effect of the catalyst, temperature, hydrogen partial pressure, and solvent employed on the product distribution. This review will aid not just in understanding the interrelations between the nature of the catalyst, HDO mechanism, and product distribution but will also provide thoughtful directions for the applications of HDO in real bio-oil upgradation.

Simultaneous Pd Nanoparticle Deposition and Enhancement in the Surface Oxygen Vacancy of Bi2MoO6 Nanoflakes for Room Temperature Vanillin Hydrodeoxygenation

“…The literature survey demonstrates that a series of noble metal-based catalysts including Au, Pd, Ru, Rh, and Pt have been reported so far for vanillin HDO to MMP. 11,13,31 These metals have been supported over various supports such as zeolites, metal oxides, g-C 3 N 4 , carbon, MOFs, etc. 11,13 Moreover, the role of oxygen vacancies in deoxygenation reactions has also been established in the literature.…”

Sustainable Synthesis of Drop-In Chemicals from Biomass via Chemical Catalysis: Scopes, Challenges, and the Way Forward

“…In a two-step strategy, lignin is first depolymerized into phenolics, which are then deoxygenated into aromatic hydrocarbons, including BTX. 164 Different classes of heterogeneous catalysts have been produced that offer varying levels of selectivity toward aromatic hydrocarbons, which are then fractionated by distillation. Due to the apparent complexity of native lignin, many studies attempted their value addition strategies on lignin model compounds and chemically altered lignin obtained during other processes.…”

Integrated design of an amination process of lignin oxygenated model compounds to synthesize cyclohexylamine: catalyst nanostructure engineering and catalytic conditional strategy

“…Extensive literature shows that oxides, carbides, sulfides, and nitrides tend to break C–O bonds and retain the aromaticity of the benzene ring, which is not conducive to the selective generation of intermediates. 36–39 To the best of our knowledge, there is only one report on nitrogen-doped carbon-supported cobalt nitride catalysts that can achieve the conversion of eugenol to propylcyclohexanol. 40 For transition metal phosphides with acidic sites, at low temperatures, the aromatic ring of the model compounds would be adsorbed and hydrogenated on the catalyst surface to form CHOL.…”