Hybrid Approach for Selective Sulfoxidation via Bioelectrochemically Derived Hydrogen Peroxide over a Niobium(V)–Silica Catalyst

Abstract

In this work, we demonstrate a combined bioelectrochemical and inorganic catalytic system for resource recovery from wastewater. We designed a microbial peroxide producing cell (MPPC) for hydrogen peroxide (H 2 O 2 ) production and used this bioelectrochemically derived H 2 O 2 as a green oxidant for sulfoxidation, an industrial reaction used for chemical synthesis and oxidative desulfurization of transportation fuels. We operated an MPPC equipped with a gas diffusion electrode cathode for six months, achieving a peak current density above 1.4 mA cm −2 with 60% average acetate removal and 61% average anodic Coulombic efficiency. We evaluated several cathode buffers under batch and continuousflow conditions for solubility and pH compatibility with downstream catalytic systems. During 24-h batch tests, a phosphatebuffered MPPC achieved a maximum H 2 O 2 concentration of 4.6 g L −1 and a citric acid−phosphate-buffered MPPC obtained a moderate H 2 O 2 concentration (3.1 g L −1 ) at a low energy input (1.6 Wh g −1 H 2 O 2 ) and pH (10). The MPPC-derived H 2 O 2 was used directly as an oxidant for the catalytic sulfoxidation of 4-hydroxythioanisole over a solid niobium(V)−silica catalyst. We achieved 82% conversion of 50 mM 4-hydroxythioanisole to 4-(methylsulfinyl)phenol with 99% selectivity with a 0.5 mol % catalyst loading in 100 min in aqueous media. Our results demonstrate a new and versatile approach for valorization of wastewater through continuous production of H 2 O 2 and its subsequent use as a selective green oxidant in aqueous conditions for green chemistry applications.

Ionic Liquid Stabilized Niobium Oxoclusters Catalyzing Oxidation of Sulfides with Exceptional Activity

“…The results meant that the rate‐limiting transition state could not only be involved in the conversion of thioether, but also in the activation progress of H 2 O 2 , which is consistent with that of the sulfoxidation process reported previously . Additionally, the dependence of the reaction rate of thioanisole on the temperature (Arrhenius plots, 278–298 K) was shown in Figure .…”

“…The linearity of the Arrhenius plots was examined to determine the activation energy, which was E a =36.1 kJ mol −1 . The activation energy under the present conditions was lower than or comparable with that of previous work on Nb‐catalyzed thioether oxidation …”

Valorization of Lignin under Mild Conditions: Biorefining Flavonoids and Lignin Nanoparticles

“…To control the pH increase, it was initially filled with a 179 mmol·L –1 pH 6 phosphate buffer (21.3 g·L –1 NaH 2 PO 4 ·H 2 O and 3.5 g·L –1 Na 2 HPO 4 ). At least twice a day, the pH of the catholyte was monitored with a pH meter (Mettler Toledo SevenCompact S210) and the H 2 O 2 concentration was determined by the ammonium metavanadate colorimetric method. , The pH and the concentration of the bioproduced H 2 O 2 of the catholyte were controlled by varying its residence time in the cathode chamber. The catholyte was harvested when it reached a pH between 10 and 11 (typically, after 24 h of operation) and stored at 4 °C until used.…”

“…They rely on colonies (biofilms) of exoelectrogenic bacteria (e.g., Shewanella oneidensis,Geobacter sulfurreducens) for the treatment of wastewaters rich in volatile fatty acids (VFAs) . In this work, we use the microbial peroxide-producing cell (MPPC, a type of MEC) described by Griffin et al This cell generates H 2 O 2 via the two-electron partial reduction of O 2 (O 2 + 2H + + 2e – → H 2 O 2 ). In an acetate-fed MEC, this reaction is exergonic, although an external electrical potential is usually applied to increase the reaction rate .…”

“…In this work, we use the microbial peroxide-producing cell (MPPC, a type of MEC) described by Griffin et al This cell generates H 2 O 2 via the two-electron partial reduction of O 2 (O 2 + 2H + + 2e – → H 2 O 2 ). In an acetate-fed MEC, this reaction is exergonic, although an external electrical potential is usually applied to increase the reaction rate . It is important to note that protons are consumed in the reduction of oxygen, resulting in an increase in pH in the cathode chamber.…”