A Comprehensive Review of Catalytic Hydrodeoxygenation of Lignin-Derived Phenolics to Aromatics

Abstract

Single-ring aromatic compounds including BTX (benzene, toluene, xylene) serve as essential building blocks for high-performance fuels and specialty chemicals, with extensive applications spanning polymer synthesis, pharmaceutical manufacturing, and aviation fuel formulation. Current industrial production predominantly relies on non-renewable petrochemical feedstocks, posing the dual challenges of resource depletion and environmental sustainability. The catalytic hydrodeoxygenation (HDO) of lignin-derived phenolic substrates emerges as a technologically viable pathway for sustainable aromatic hydrocarbon synthesis, offering critical opportunities for lignin valorization and biorefinery advancement. This article reviews the relevant research on the conversion of lignin-derived phenolic compounds' HDO to benzene and aromatic hydrocarbons, systematically categorizing and summarizing the different types of catalysts and their reaction mechanisms. Furthermore, we propose a strategic framework addressing current technical bottlenecks, highlighting the necessity for the synergistic development of robust heterogeneous catalysts with tailored active sites and energy-efficient process engineering to achieve scalable biomass conversion systems.

Keywords: aromatic hydrocarbon; benzene; electrocatalytic hydrogenation; hydrodeoxygenation; lignin; phenolic compounds.

Figure 1

The schematic diagram of the composition of lignocellulosic biomass [23]. Copyright 2016 Royal Society of Chemistry.

Figure 2

(a) Mechanism of Pd-Fe synergy in HDO of m-cresol [43]. Copyright 2014 American Chemical Society. (b) The HDO reaction of phenol over Pd/SiO₂ and Pd/Nb₂O₅ [44]. Copyright 2017 Elsevier. (c) Reaction scheme for the HDO of phenolics over Pd supported on various oxides [47]. Copyright 2021 American Chemical Society.

Figure 3

(a) Reaction pathway of p-cresol HDO over the Ru/Nb₂O₅-SiO₂ catalyst [52]. Copyright 2017 Elsevier. (b) Water-assisted HDO of phenol over the Ru/TiO₂ catalyst [53]. Copyright 2015 American Chemical Society. (c) The combination of N₂ activation and an HDO reaction over the Ru/TiO₂ catalyst [54]. Copyright 2019 Springer Nature. (d) The selective HDO of phenolics to BTX over Ru/HZSM-5 in water [55]. Copyright 2016 Royal Society of Chemistry. (e) Schematic synthetic process for MoO_x-decorated ZrO₂-supported Ru nanocluster catalysts; (f) The selective HDO of anisole to benzene over the Ru/MoO_x-ZrO₂ catalyst [56]. Copyright 2021 American Chemical Society.

Figure 4

(a) The HDO reaction of m-cresol over the Pt/TiO₂ catalyst [61]. Copyright 2016 American Chemical Society. (b) Mechanism of the direct deoxygenation route of m-cresol on a schematic molybdenum oxide-site species [62]. Copyright 2017 Elsevier. (c) The upgrading of phenolics to BTX over the different Ni@silicalite-1 catalysts [63]. Copyright 2021 American Chemical Society. (d) Possible reaction mechanism of the HDO conversion of guaiacol over the Fe/SiO₂ catalyst [39]. Copyright 2012 Elsevier. (e) The HDO of anisole to benzene over the Mn-doped Cu/Al₂O₃ catalysts; (f) the mechanism for the anisole HDO on Cu/MnAlOx with the Mn/Cu molar ratio increasing [64]. Copyright 2021 Elsevier.

Figure 5

(a) The structure of the Pd layer in the matrix on the Fe (110) surface. (b) Adsorption conformation of phenol on the Fe (110) surface Pd atom. The distance from the adsorbate to the palladium atom increases from position 1 to position 3 [84]. Copyright 2013 Elsevier. (c) The possible mechanism of the anisole HDO over the RuFe/meso-TiO₂ catalyst [86]. Copyright 2018 Elsevier.

Figure 7

(a) The performance of the In on Ni/SiO₂ catalyst in the HDO of anisole with different products [93]. Copyright 2017 Elsevier. (b) Schematic representation of the structure of the bimetallic Ni-Re catalyst before (left) and after (right) reduction at 450 °C [95]. Copyright 2017 Elsevier. (c) Phenol adsorption onto the Ni (A) surface and (B) phenol adsorption onto the (Re)Ni (111) surface [95]. Copyright 2017 Elsevier. (d) The plausible reaction mechanism in the HDO of anisole on Ni_xGa/SiO₂ [96]. Copyright 2017 Elsevier. (e) The proposed mechanism of modification between aromatic selectivity, oxygen vacancies, and H₂ absorption [97]. Copyright 2021 American Chemical Society.

Figure 8

(a) The direct HDO of m-cresol over WO_x-decorated Pt/C catalysts [103]. Copyright 2018 American Chemical Society. (b) The tentative reaction mechanism for the SSH reaction of anisole on a RuW/SiO₂ catalyst [104]. Copyright 2019 Springer science.

Figure 9

(a) Surface engineering of the CoMoS catalyst for the conversion of the phenolic HDO to the product BTX; (b) synthesis diagram of cobalt-doped MoS₂ nanohybrids [112]. Copyright 2019 American Chemical Society. (c) Illustration of the hydrogen-flow-induced in situ formation of active CoMoS sites for the selective HDO of p-cresol to toluene [104]. Copyright 2020 American Chemical Society. (d) Tailoring of surface acidic sites in Co-MoS₂ catalysts for the HDO of p-cresol to toluene [114]. Copyright 2021 American Chemical Society.

Figure 11

(a) The proposed reaction routes of the HDO of guaiacol over the Ni₂P catalyst [129]. Copyright 2014 Elsevier. (b) Different Ni sites on Ni₂P for the deoxygenation of cresol [132]. Copyright 2017 Elsevier. (c) The HDO of anisole to benzene over the Fe₂P catalyst; (d) the possible reaction route of anisole HDO over Fe₂P [135]. Copyright 2020 Royal Society of Chemistry.

Figure 6

(a) Hydrogen spillover enhanced by oxygenate additives during catalysis; (b) the suggested HDO route of guaiacol to produce BTX [88]. Copyright 2022 Springer Nature.

Figure 10

(a) Schematic illustration of the preparation of the Mo-Co₉S₈/Al₂O₃ catalyst; (b) illustration on the catalytic mechanism of the DPE HDO reaction over the eMo-Co₉S₈ site [115]. Copyright 2022 Elsevier.

Figure 12

The HDO of anisole to BTX by a MoC_x-encapsulated FAU zeolite catalyst [146]. Copyright 2017 American Chemical Society.