AuFe₃@Pd/γ-Fe₂O₃ Nanosheets as an In Situ Regenerable and Highly Efficient Hydrogenation Catalyst

Abstract

Heterogenous Pd catalysts play a pivotal role in the chemical industry; however, it is plagued by S 2− or other strong adsorbates inducing surface poisoning long term. Herein, we report the development of AuFe 3 @Pd/γ-Fe 2 O 3 nanosheets (NSs) as an in situ regenerable and highly active hydrogenation catalyst. Upon poisoning, the Pd monolayer sites could be fully and oxidatively regenerated under ambient conditions, which is initiated by •OH radicals from surface defect/Fe Tetra vacancy-rich γ-Fe 2 O 3 NSs via the Fenton-like pathway. Both experimental and theoretical analyses demonstrate that for the electronic and geometric effect, the 2−3 nm AuFe 3 intermetallic nanocluster core promotes the adsorption of reactant onto Pd sites; in addition, it lowers Pd's affinity for •OH radicals to enhance their stability during oxidative regeneration. When packed into a quartz sand fixed-bed catalyst column, the AuFe 3 @Pd/γ-Fe 2 O 3 NSs are highly active in hydrogenating the carbon−halogen bond, which comprises a crucial step for the removal of micropollutants in drinking water and recovery of resources from heavily polluted wastewater, and withstand ten rounds of regeneration. By maximizing the use of ultrathin metal oxide NSs and intermetallic nanocluster and monolayer Pd, the current study demonstrates a comprehensive strategy for developing sustainable Pd catalysts for liquid catalysis.

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

“…This is far below the requirement for a practical nitrate reduction electrocatalyst, which must have a turnover frequency (TOF) of >1 s –1 at > – 0.1 V vs reversible hydrogen electrode (RHE) over a three-year lifetime while selectively producing desired products in alkaline or acidic media. To enhance the activity and selectivity of Pd catalysts, the incorporation of a second metal atom has proved to be an effective strategy. , Meanwhile, bimetallic Pd catalysts also show high activity and selectivity in environmentally relevant reactions like H 2 O 2 synthesis ,,,, and hydrodehalogenation. ,,,,,− In this section, taking the reduction/electrochemical reduction of NO 3 – as an example, the mechanism aspects of how the bimetallic effect improve the catalytic performance of Pd are discussed (Figure ).…”

“…Rapid industrialization has led to an exponential increase in the discharge of various pollutants into the environment, particularly in bodies of water. Halogenated organics, such as polychlorinated biphenyls, organic flame retardants, vinyl chloride, halogenated phenols, heavy metals, and oxylate ions (NO 3 – /NO 2 – , BrO 4 – /BrO 3 – , ClO 4 – /ClO 3 – ), are the most frequently detected pollutants in the water environment, posing lasting and significant public health concerns. To provide clean drinking water and eliminate ecological risks, various water treatment technologies have been proposed, including physical adsorption, biochemical processing, and chemical transformation. , These technologies, either individually or in combination, form the foundation of the water purification process for treating industrial wastewater, municipal sewage, and raw water to achieve a sustainable environment and safe drinking water.…”

“…Unlike AOP processes that require the addition of H 2 O 2 , PMS as reactant, and transition metal ions as activator, the reduction process utilizes H 2 that could be in situ generated from the electrolyzing of water, or electrons themselves, which are from renewable electricity. Moreover, for concentrated pollutants such as wastewater discharged from factories contaminated with high concentrations of organics , or reverse osmosis brine water with high concentration of oxylate ion, , the reduction process can facilitate the transformation of waste into value-added chemicals. When coupled with the subsequent resource recovery processes, , this not only reduces the burden on terminal water treatment plants but also lowers the overall treatment costs. High safety and broad applicability.…”

“…Among the PGMs, the global annual supply of Pt and Pd ranges from 170 to 230 tons, which is about 10 times higher than that of Rh and Ru and 40 times higher than that of Ir (). Moreover, Pd demonstrates higher activity and selectivity toward a wide spectrum of reactions, ,,,− including catalyzed or electrocatalyzed hydrodehalogenation (HDH or EHDH) ,,, and oxyanion reduction. , By further optimizing the composition, , size, metal–support interaction, , and the interfacial microenvironment, the catalytic performance of Pd can be increased by another 10-fold or higher. In consequence, the application of Pd-based nanotechnology for water treatment has aroused continuous research interest.…”

Plasma synthesis of oxygen vacancy-rich CuO/Cu2(OH)3NO3 heterostructure nanosheets for boosting degradation performance

“…1–4 Especially in the textile industry, the dyeing process produces wastewater with strong colors, high chemical oxygen demand, and low biodegradability, causing serious environmental problems. 5–8 Therefore, the development of a green method for eliminating organic pollution has become an important issue in environmental remediation. 9…”