Alanine Formation in a Zero‐Gap Flow Cell and the Role of TiO2/Ti Electrocatalysts

The room-temperature, electrocatalytic reductive amination (ERA) of biomass-derivable precursors can be a sustainable method to produce amino acids. In order to further the adoption of this method, three different Ti, and TiO₂/Ti felt electrodes were used to synthesize alanine in a flow electrolyzer. Hydrothermally synthesized TiO₂/Ti felt electrodes showed the highest conversion efficiency. It was found that excess NH₂OH dramatically decreased the conversion efficiency. A maximum efficiency of 75 % was attained with the hydrothermally synthesized felts when operated at a cell potential of 2.0 V, and an electrolyte flow rate of 10 mL/h.

Abstract

The electrochemical synthesis of -amino acids at room temperature and pressure is a sustainable alternative to conventional methods like microbial fermentation and Strecker synthesis. A custom-built zero-gap flow electrolyzer was used to study the electrosynthesis of alanine via the electrocatalytic reductive amination (ERA) of the corresponding biomass-derivable -keto acid precursor – pyruvic acid (PA), and hydroxylamine (NH₂OH) at very low pH. Non-toxic, abundant, and easy to prepare TiO₂/Ti electrocatalysts were utilized as the cathode. Three TiO₂/Ti felt electrodes with different oxide thicknesses were prepared and their characterization results were correlated with their respective electrochemical performance in terms of Faradaic efficiency , and partial current density . Cyclic voltammetry indicated a different electrocatalytic reduction process on hydrothermally treated electrodes, compared to thermally oxidized ones. Hydrothermally treated electrodes were also found to have the thickest porous anatase layer and achieved 50–75 % alanine conversion efficiencies. Optimization showed that the cell potential, reactant flow rate and the PA: NH₂OH ratio were crucial parameters in determining the conversion efficiency. and were found to significantly decrease when an excess of is used and, an optimal alanine of 75 % was achieved at 2.0 V applied cell potential and 10 mL/h reactant flow rate.

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