Selective Electrochemical Oxidation of Lactic Acid Using Iridium-Based Catalysts

Abstract

Catalysts that allow for selective oxidation of organic compounds in solution are useful tools in chemical synthesis, waste remediation, and renewable energy storage schemes. Of these, iridium oxide and iridium-based molecular compounds are frequently employed as catalysts to oxidize substrates ranging from small organic molecules to water. Here, we study the mechanism and evaluate the potential of iridium-based catalysts for small molecule oxidation in wastewater treatment, using lactic acid as a substrate. By investigating the reaction products, kinetic isotope effects, and electrochemical properties of iridium oxide and a molecular analogue on a high surface area antimony-doped tin oxide (ATO) support, we find evidence for a new iridium-catalyzed pathway for lactic acid oxidation. Applying this at concentrations representative of effluent from dairy production processes, we show that iridium oxide can selectively remove small amounts of lactic acid from water by oxidizing it to CO2 with concomitant cathodic production of H2 by proton reduction.

Application of Advanced Oxidation Processes for the Treatment of Recalcitrant Agro-Industrial Wastewater: A Review

“…The use of iridium-based catalyst in electrochemical oxidation allowed a complete oxidation of lactic acid into mainly CO 2 , from water samples. [110] Rivas et al [105] report the study of cheese whey wastewater also by coagulation/flocculation, testing three different coagulants-FeSO 4 , Al 2 (SO 4 ) 3 and FeCl 3 . Iron salts (FeSO 4 and FeCl 3 ) were more efficient under optimal conditions: using 250 ppm of coagulant at pH 8.5, where 50 and 60% of COD and BOD removal were obtained, respectively.…”

“…Response surface methodology has been an important procedure to use in the optimization of wastewater treatments processes by reducing the number of experiments, improving desire results and reducing costs. Furthermore, Chen et al [110] successfully tested the use of iridium-based as heterogeneous catalyst in electrochemical oxidation for the acid lactic wastewater oxidation. During oxidation there was only acetic acid and formic acid as intermediates which were oxidized into carbon dioxide and hydrogen gas with the complete oxidation [110].…”

“…Furthermore, Chen et al [110] successfully tested the use of iridium-based as heterogeneous catalyst in electrochemical oxidation for the acid lactic wastewater oxidation. During oxidation there was only acetic acid and formic acid as intermediates which were oxidized into carbon dioxide and hydrogen gas with the complete oxidation [110]. Electrochemical treatment of dairy wastewaters under different operational conditions reveals to be a feasible alternative to other treatments.…”

Corrosion Potential Modulation on Lead Anodes Using Water Oxidation Catalyst Coatings

“…Second, reduction in manganese consumption is a cost driver for zinc refining, as is reduction in electricity consumption, both of which could be tackled by a competent heterogeneous water oxidation catalyst. This strategy is also proven, as iridium is used in the electrochemical industry as an anode protective layer, but is costly [28,29]. In this study, we investigate the properties of a pre-applied cobalt oxide-based catalyst, Co-dppe, to investigate how the surface electrochemistry of the Pb anodes is changed compared to the Co-and Mn-based solution phase additives that form catalytic layers in-situ.…”

Carbon and energy footprint of electrochemical vinegar wastewater treatment

“…MOx + H2O → MOx(OH -) + H + + e -(5) The hydroxyl radical is absorbed on the electrode surface and organic matter decays: R + MOx(OH)z → (z/2)O2 + zH + +2e -+ MOx (6) Again, details of the process can be reached from [14][15][16][17]. Performance differences of these two reactions will be illustrated and discussed in the experimental results section.…”