Electrochemical Lignin Oxidation Reaction on CuO: in situ Spectroelectrochemical Point of View

Lignins are macromolecules present in biomass tissues, the third most present component. This compound is frequently used as a thermoelectric fuel generating cheap energy, however, burns the most abundant renewable source of aromatic structures in the world. For obtaining useful low molecular weight compounds, depolymerization needs to be considered. One way of doing it is the lignin oxidation reaction, which can be catalytic or non-catalytic. The non-catalytic uses hard chemicals, temperature and pressure, and can present lower selectivity, further oxidizing monoaromatic products. The use of catalysts, especially electrocatalysts, make the conditions mild and increases the selectivity, however, the reaction pathway followed is still under debate. It is difficult to find proposals in the literature that consider the heterogeneous catalyst-lignin interaction, so in this work we applied in situ spectroelectrochemical techniques in the infrared region to check this, using commercial CuO catalyst powder as catalyst and sugarcane lignin in 2.0 mol L-1 KOH. The spectra were registered in external reflection-absorption configuration, deconvoluted and the intensities and position of the bands were analyzed. For a deeper understanding of the chemical adsorption, the first step of lignin electro-oxidation, computational simulations were performed for a model lignin molecule with the C(gamma) as the C atom closest to the CuO surface. The Cα-Cβ breaking linkages could be followed and some improved mechanistic steps were proposed.