Long-Term Continuous Test of H 2 -Induced Denitrification Catalyzed by Palladium Nanoparticles in a Biofilm Matrix

Catalyzed reduction processes have been recognized as important and supplementary technologies for water treatment, with the specific aims of resource recovery, enhancement of bio/chemicaltreatability of persistent organic pollutants, and safe handling of oxygenate ions. Palladium (Pd) has been widely used as a catalyst/ electrocatalyst in these reduction processes. However, due to the limited reserves and high cost of Pd, it is essential to gain a better understanding of the Pd-catalyzed decontamination process to design affordable and sustainable Pd catalysts. This review provides a systematic summary of recent advances in understanding Pd-catalyzed reductive decontamination processes and designing Pd-based nanocatalysts for the reductive treatment of water-borne pollutants, with special focus on the interactions and transformation mechanisms of pollutant molecules on Pd catalysts at the atomic scale. The discussion begins by examining the adsorption of pollutants onto Pd sites from a thermodynamic viewpoint. This is followed by an explanation of the molecular-level reaction mechanism, demonstrating how electron-donors participate in the reductive transformation of pollutants. Next, the influence of the Pd reactive site structure on catalytic performance is explored. Additionally, the process of Pd-catalyzed reduction in facilitating the oxidation of pollutants is briefly discussed. The longevity of Pd catalysts, a crucial factor in determining their practicality, is also examined. Finally, we argue for increased attention to mechanism study, as well as precise construction of Pd sites under batch synthesis conditions, and the use of Pd-based catalysts/electrocatalysts in the treatment of concentrated pollutants to facilitate resource recovery.

Section: Pathways For Pd-catalyzed Environmental Reductionmentioning

confidence: 99%

Critical Review of Pd-Catalyzed Reduction Process for Treatment of Waterborne Pollutants

Ran,

Zhao,

Zhang

et al. 2024

“…Conventional methods of delivering H 2 through bubbling and/or with a high-pressure headspace waste H 2 and can create a combustible atmosphere due to off-gassing. Depositing catalysts on nonporous hollow-fiber membranes provides precise bubble-free delivery of H 2 to the catalyst, which overcomes inefficient H 2 transfer due to low H 2 solubility and H 2 off-gassing that could create a combustion hazard . The counterdirectional diffusion of H 2 and the oxidized contaminant makes the rate of H 2 delivery self-controlled.…”

Section: Introductionmentioning

confidence: 99%

Method of H₂ Transfer Is Vital for Catalytic Hydrodefluorination of Perfluorooctanoic Acid (PFOA)

Long,

Chen,

Senftle

et al. 2024

Self Cite

The efficient transfer of H 2 plays a critical role in catalytic hydrogenation, particularly for the removal of recalcitrant contaminants from water. One of the most persistent contaminants, perfluorooctanoic acid (PFOA), was used to investigate how the method of H 2 transfer affected the catalytic hydrodefluorination ability of elemental palladium nanoparticles (Pd 0 NPs). Pd 0 NPs were synthesized through an in situ autocatalytic reduction of Pd 2+ driven by H 2 from the membrane. The Pd 0 nanoparticles were directly deposited onto the membrane fibers to form the catalyst film. Direct delivery of H 2 to Pd 0 NPs through the walls of nonporous gas transfer membranes enhanced the hydrodefluorination of PFOA, compared to delivering H 2 through the headspace. A higher H 2 lumen pressure (20 vs 5 psig) also significantly increased the defluorination rate, although 5 psig H 2 flux was sufficient for full reductive defluorination of PFOA. Calculations made using density functional theory (DFT) suggest that subsurface hydrogen delivered directly from the membrane increases and accelerates hydrodefluorination by creating a higher coverage of reactive hydrogen species on the Pd 0 NP catalyst compared to H 2 delivery through the headspace. This study documents the crucial role of the H 2 transfer method in the catalytic hydrogenation of PFOA and provides mechanistic insights into how membrane delivery accelerates hydrodefluorination.

“…Pd 0 NPs immobilized in the biofilm matrix adsorb H 2 and cleave it to form activated H atoms (i.e., H*) to form [Pd–H*], which can reduce a number of drinking-water contaminants, particularly NO 2 – . − Pd 0 NP-catalyzed hydrogenation can lower intracellular competition for NADH and accelerate respiration, which must occur intracellularly. Previous work documented an acceleration of the NO 3 – reduction due to synchronous enzymatic and catalytic reductions: NO 3 – reduction to NO 2 – was entirely accomplished by bacteria, while NO 2 – reduction to N 2 was primarily catalyzed by Pd 0 NPs. − When ClO 4 – and NO 3 – co-reductions occur, diversion of electron flow away from intracellular NADH consumption for NO 2 – reduction to extracellular Pd 0 NP-catalyzed reduction may enhance ClO 4 – reduction during NO 3 – co-reduction by lowering the intracellular demand for NADH.…”

Section: Introductionmentioning

confidence: 99%

Biogenic Palladium Improved Perchlorate Reduction during Nitrate Co-Reduction by Diverting Electron Flow in a Hydrogenotrophic Biofilm

Zhou,

Yang,

et al. 2024

Self Cite

Microbial reduction of perchlorate (ClO 4 − ) is emerging as a cost-effective strategy for groundwater remediation. However, the effectiveness of perchlorate reduction can be suppressed by the common cocontamination of nitrate (NO 3 − ). We propose a means to overcome the limitation of ClO 4 − reduction: depositing palladium nanoparticles (Pd 0 NPs) within the matrix of a hydrogenotrophic biofilm. Two H 2 -based membrane biofilm reactors (MBfRs) were operated in parallel in long-term continuous and batch modes: one system had only a biofilm (bio-MBfR), while the other incorporated biogenic Pd 0 NPs in the biofilm matrix (bioPd-MBfR). For longterm co-reduction, bioPd-MBfR had a distinct advantage of oxyanion reduction fluxes, and it particularly alleviated the competitive advantage of NO 3 − reduction over ClO 4 − reduction. Batch tests also demonstrated that bioPd-MBfR gave more rapid reduction rates for ClO 4 − and ClO 3 − compared to those of bio-MBfR. Both biofilm communities were dominated by bacteria known to be perchlorate and nitrate reducers. Functional-gene abundances reflecting the intracellular electron flow from H 2 to NADH to the reductases were supplanted by extracellular electron flow with the addition of Pd 0 NPs.