Electrochemical biomass valorization of furfural to maleic acid by modulating selectivity with Bi-doped lead oxide

Abstract

Maleic acid (MA) production from furfural (FF) is a promising electrochemical oxidation reaction to convert biomass into valuable platform chemicals. However, a library of oxidation activities needs to be studied more. Herein, we demonstrate that Bi doping in lead oxide is effective in tuning the activity for complicated FF oxidation reactions. Bi-doped lead oxide (PbBiO_x) can selectively produce MA from the electrochemical FF oxidation reaction (FFOR), leading to a maximum MA yield of 57% with an optimal Bi content of Pb_0.9Bi_0.1O_x. Its selectivity, the relative yield of MA in relation to 5-hydroxy-2(5H)-dihydrofuran-2-one (HFN), is largely enhanced by 17 times, compared to pristine PbO_x. We propose that Bi affects the oxidation state of Pb and thus the selectivity of the oxidation reaction, which is supported by a series of product analyses of the electrochemical oxidation of FF (reactant), HFN (intermediate), and maleic acid (product). While PbO_x prepared by a simple thermal decomposition method is composed of a PbO₂ and Pb₃O₄ mixture, the ratio of PbO₂ to Pb₃O₄ decreases in PbBiO_x, suppressing active Pb⁴⁺ under the applied potentials. PbBiO_x exhibited a lower conversion rate of FF as well as greater preservation of the carbon source during the FFOR than PbO_x, and Bi-doping was also shown to be effective in retarding the overoxidation of MA to CO₂. Our study shows that mixed metal oxides can be effective in adjusting the oxidation activity and contribute to selective electrosynthesis from multi-step biomass conversion.