Electrocatalytic degradation of rice straw lignin in alkaline solution through oxidation on a Ti/SnO₂–Sb₂O₃/α-PbO₂/β-PbO₂ anode and reduction on an iron or tin doped titanium cathode

Abstract

A novel procedure for selective production of biomass-based compounds by electrochemical conversion has been developed in this work.

Electrochemical Lignin Conversion

“…[53] The mechanism of electrooxidation on the active electrode (e. g., Ti/PbO 2 ) is shown in Equations (4)-(7). [59] It is important to note that the direct electrooxidation of lignin on electrodes can control the potential to prevent oxygen evolution. [Eq.…”

“…However, the complex structure of lignin makes it very difficult to dissolve in common organic solvents. [82] Alkaline solutions (e. g., NaOH, KOH) have been widely used as the electrolyte in many lignin electrooxidation studies [10,31,44,48,59,[83][84][85][86][87][32][33][34]37,[40][41][42][43] due to increased solubility for lignin and high electron/ion conductivity. However, electrolysis in aqueous solution is limited by the water splitting reaction at 1.23 V, severely restricting the potential window for electrochemical reactions.…”

“…[34,59,87,152,153] The advantage of a hybrid approach results from simultaneous generation of reactive oxygen species and hydrogen in situ, which can be used for electro-oxidation and electro-reduction of lignin and its intermediates. [59] Li and co-workers investigated a hybrid electrochemical degradation of bamboo lignin using a Cu cathode and Pb/PbO 2 anode in sodium hydroxide solution, [34] and identified vanillin, syringaldehyde and p-coumaric acid as the main products. Later, Li and co-workers reported a hybrid electro-redox depolymerization of corn stover lignin in alkali solution by using a Pb/PbO 2 anode and a Cu/NiÀ Mo-Co cathode.…”

“…Similarly, a hybrid electro-redox depolymerization of rice straw lignin at a constant current with 1.0 M NaOH as electrolyte solution to produce biomass-based chemicals was reported. [59] The electrocatalysis could effectively cleavage of aryl CÀ O and CÀ C bonds among phenylpropyl units in rice straw lignin to produce phenols, aromatic hydrocarbons, aromatic esters, aromatic ketones, aromatic acids and aromatic aldehydes. Later, a hybrid electro-redox method was further applied to depolymerize wheat straw lignin using the same anode and alloyed materials cathode [e. g., stainless steel plates (304, 316 L, 202, 410 S, P110) and high-speed steel (HSS) plates (FeW 9 Cr 4 V 5 , FeW 9 Cr 4 Mo 3 V, and FeW 9 Cr 4 V 5 Co 3 )] with different electrode potentials in alkaline solution.…”

Greener Routes to Biomass Waste Valorization: Lignin Transformation Through Electrocatalysis for Renewable Chemicals and Fuels Production

“…Jia et al studied the electrochemical redox reactions of rice straw lignin, using modified PbO 2 (Ti/SnO 2 -Sb 2 O 3 /a-PbO 2 /b-PbO 2 )a node and titanium-based cathodes (Ti/Fe, Ti/Cu, or Ti/ Cu/Sn). [106] The study detected and quantified ten oxidation and six reduction products.H ighesty ields of guaiacol, 3,4,5-trimethoxytoluene, 2-hydroxy-5-methylacetophenone, 4-hydroxy-3-methoxy-phenylacetone, and vanillin were obtained with Ti/ Cu/Sn. Syringol formation was only promoted by Ti/Fe while Ti by itself gave the highest yield of 1,2,3-trimethoxynenzene.…”