H₂-Based Membrane Catalyst-Film Reactor (H₂-MCfR) Loaded with Palladium for Removing Oxidized Contaminants in Water

Abstract

Scalable applications of precious-metal catalysts for water treatment face obstacles in H2-transfer efficiency and catalyst stability during continuous operation. Here, we introduce a H2-based membrane catalyst-film reactor (H2-MCfR), which enables in situ reduction and immobilization of a film of heterogeneous Pd0 catalysts that are stably anchored on the exterior of a nonporous H2-transfer membrane under ambient conditions. In situ immobilization had >95% yield of Pd0 in controllable forms, from isolated single atoms to moderately agglomerated nanoparticles (averaging 3–4 nm). A series of batch tests documented rapid Pd-catalyzed reduction of a wide spectrum of oxyanions (nonmetal and metal) and organics (e.g., industrial raw materials, solvents, refrigerants, and explosives) at room temperature, owing to accurately controlled H2 supply on demand. Reduction kinetics and selectivity were readily controlled through the Pd0 loading on the membranes, H2 pressure, and pH. A 45-day continuous treatment of trichloroethene (TCE)-contaminated water documented removal fluxes up to 120 mg-TCE/m2/d with over 90% selectivity to ethane and minimal (<1.5%) catalyst leaching or deactivation. The results support that the H2-MCfR is a potentially sustainable and reliable catalytic platform for reducing oxidized water contaminants: simple synthesis of an active and versatile catalyst that has long-term stability during continuous operation.

Hydrodefluorination of Perfluorooctanoic Acid in the H2-Based Membrane Catalyst-Film Reactor with Platinum Group Metal Nanoparticles: Pathways and Optimal Conditions

“…This peaking at 1.2 g Pd 0 /m 2 occurred because the defluorination of PFOA with H 2 occurred mainly at the water–Pd 0 interface. We hypothesize that while increasing the loading of nanoparticles increased the total active surface area, excessive Pd 0 coverage resulted in aggregation of Pd 0 NPs, which decreased the accessible specific surface area and led to lower catalytic activity . In addition, a thick and agglomerated Pd film may have hindered H 2 transfer to Pd 0 sites near the bulk liquid.…”

“…We hypothesize that while increasing the loading of nanoparticles increased the total active surface area, 28 excessive Pd 0 coverage resulted in aggregation of Pd 0 NPs, which decreased the accessible specific surface area and led to lower catalytic activity. 14 In addition, a thick and agglomerated Pd film may have hindered H 2 transfer to Pd 0 sites near the bulk liquid. Because 1.2 g Pd 0 /m 2 gave the best removal and defluorination performance, it was chosen as the optimal addition in this study.…”

“…A H 2 -based membrane catalyst-film reactor (H 2 -MCfR) is a novel technology that can overcome the challenges of low efficiency and safety of H 2 delivery by accurately supplying H 2 gas in a bubble-free form through nonporous membrane fibers. This efficient and accurate way in delivering H 2 enables the formation of a robust catalyst film, high-efficiency utilization of H 2 , and minimal combustion potential. , …”

Highly Efficient Reductive Detoxification of Sulfamethoxazole by Palladium Nanoparticles Deposited on H2-Transfer Membranes

“…Excessive agglomeration of PdNPs would not only block the contact between catalytic active sites and SMX but also induce greater mass transfer resistance between H 2 and PdNPs, thus lowering the SMX removal rate. 40 It has also been reported that an excessive Pd loading (over 0.44 g/m 2 ) could lead to the decrease of nitrite reduction by 22% in a similar MPfR system. 40 According to these observations, we can conclude that the Pd dosage has a crucial impact on the SMX removal efficiency and should be controlled at a proper level (e.g., 100 mg/dm 2 under the experimental condition) for long-term SMX removal.…”

“…According to the surface topography of the membrane at different magnifications (Figure S3), obviously nanosize Pd adhered to the membrane, verifying the successful construction of PdNPs film to the membranes, which is similar to that reported by Zhou et al (2017, 2021). 40,41 XPS was further used to analyze the valency of precipitates attached to the surface of membranes (Figure 1B), and it was found that Pd(0) was dominant, indicating Pd(II) was reduced to Pd(0), which was well-deposited to the membranes.…”