Reductive Dehalogenation of Herbicides Catalyzed by Pd⁰NPs in a H₂-Based Membrane Catalyst-Film Reactor

Abstract

More food production required to feed humans will require intensive use of herbicides to protect against weeds. The widespread application and persistence of herbicides pose environmental risks for nontarget species. Elementalpalladium nanoparticles (Pd 0 NPs) are known to catalyze reductive dehalogenation of halogenated organic pollutants. In this study, the reductive conversion of 2,4dichlorophenoxyacetic acid (2,4-D) was evaluated in a H 2 -based membrane catalystfilm reactor (H 2 -MCfR), in which Pd 0 NPs were in situ-synthesized as the catalyst film and used to activate H 2 on the surface of H 2 -delivery membranes. Batch kinetic experiments showed that 99% of 2,4-D was removed and converted to phenoxyacetic acid (POA) within 90 min with a Pd 0 surface loading of 20 mg Pd/m 2 , achieving a catalyst specific activity of 6.6 ± 0.5 L/g-Pd-min. Continuous operation of the H 2 -MCfR loaded with 20 mg Pd/m 2 sustained >99% removal of 50 μM 2,4-D for 20 days. A higher Pd 0 surface loading, 1030 mg Pd/m 2 , also enabled hydrosaturation and hydrolysis of POA to cyclohexanone and glycolic acid. Density functional theory identified the reaction mechanisms and pathways, which involved reductive hydrodechlorination, hydrosaturation, and hydrolysis. Molecular electrostatic potential calculations and Fukui indices suggested that reductive dehalogenation could increase the bioavailability of herbicides. Furthermore, three other halogenated herbicides�atrazine, dicamba, and bromoxynil� were reductively dehalogenated in the H 2 -MCfR. This study documents a promising method for the removal and detoxification of halogenated herbicides in aqueous environments.

Controllable Pyridine N-Oxidation–Nucleophilic Dechlorination Process for Enhanced Dechlorination of Chloropyridines: The Cooperation of HCO4– and HO2–

“…In the presence of HA, the dechlorination efficiency of Cl–Py reached about 82%, which was slightly lower than that in the carbonate species/H 2 O 2 process without the addition of any chemical reagent (84.5%). The phenomenon could be related to the competitive consumption of reactive species by the aromatic rings and oxygen-bearing functional groups of humic acid. , We applied the carbonate species/H 2 O 2 process to treat real Cl–Py wastewater. As shown in Figure S22, the concentration of Cl–Py decreased from 31.4 mg to 1.8 mg L –1 within 48 h. Moreover, the increased Cl – concentration was detected after 48 h of the reaction (Figure S23).…”

“…The phenomenon could be related to the competitive consumption of reactive species by the aromatic rings and oxygen-bearing functional groups of humic acid. 48,49 We applied the carbonate species/H 2 O 2 process to treat real Cl−Py wastewater. As shown in Figure S22, the concentration of Cl−Py decreased from 31.4 mg to 1.8 mg L −1 within 48 h. Moreover, the increased Cl − concentration was detected after 48 h of the reaction (Figure S23).…”

Utilizing an Integrated Flow Cathode–Membrane Filtration System for Effective and Continuous Electrochemical Hydrodechlorination

“…The slight discrepancy between the model output and the experimental data (<20% in most cases) is particularly apparent during the first 10 min of the batch-mode EHDC. This discrepancy is possibly due to relatively low pH (in the range 5− 11) in the cathode chamber during the first 10 min, which is favorable for EHDC (as discussed in Section 3.2.5); however, in the model, we have assumed a high pH (11) from the beginning of the experiment. Furthermore, competing reactions such as HER may influence the sorption of 2,4-DCP and other CPs and subsequent electron transfer as a result of generation of H 2 bubbles; however, the decrease in the rate of sorption of organics and/or electron transfer over time during EHDC as a result of H 2 generation is not included in the model.…”

Palladium Single-Atom (In)Stability Under Aqueous Reductive Conditions

“…However, most studies on SAC stability thus far have involved gas-phase systems, typically under reducing conditions (reductive reactant or atmosphere). , With the recent increasing interest in SACs for sustainable water remediation, we here observed the aggregation of Pd 1 under conditions relevant to thermocatalytic hydrodehalogenation. We monitored the real-time migration of Pd 1 into clusters in a suspension system, expanding our knowledge of SAC behavior in the aqueous phase beyond electrochemical applications. ,, Envisioning the translation from the batch reactor to H 2 -based membrane catalyst-film reactors, − our findings advance the understanding of SAC stability under reductive aqueous conditions, imperative for the informed design of catalytic nanomaterials fit for water treatment.…”