Search Results (5)

We developed and optimized an electrocatalytic filtration system to catalytically hydrodechlorinate chlorophenolic compounds. A key part of the system was the cathode, which consisted of a filter constructed with electroactive carbon nanotubes (CNTs) functionalized with atomically precise gold nanoclusters (AuNCs). In the functional membrane electrode, the AuNCs attached to the CNTs functioned as a highly effective hydrodechlorination catalyst. Additionally, the ligands of the AuNCs facilitated the binding of the AuNCs with the CNT and protected the Au core from agglomeration. Atomic H* was the primary reactive species in the system, but direct reduction by cathode electrons also contributed to the elimination of 2,4-dichlorophenol (2,4-DCP) by hydrodechlorination. The generated atomic H* was able to break the C–Cl bond to achieve the rapid hydrodechlorination of 2,4-DCP into phenol, with 91.5% 2,4-DCP removal within 120 min. The AuNC catalysts attached to the CNT exceeded the best catalytic activity of larger nanoparticles (e.g., AuNPs), while the flow-through construction performed better than a standard batch reactor due to the convection-enhanced mass transport. The study provides an environmentally friendly strategy for the elimination of pervasive halogenated organic contaminants using a highly efficient, stable and recyclable system for hydrodechlorination that integrates nanofiltration and electrochemistry. Full article

Hydrodechlorination (HDC) is a reaction that involves the use of hydrogen to cleave the C−Cl bond in chlorinated organic compounds such as chlorophenols and chlorobenzenes, thus reducing their toxicity. In this study, a palladium (Pd) catalyst, which is widely used for HDC due to its advantageous physical and chemical properties, was immobilized on alumina (Pd/Al) and graphene-based materials (graphene oxide and reduced graphene oxide; Pd/GO and Pd/rGO, respectively) to induce the HDC of 4-chlorophenol (4-CP). The effects of the catalyst dosage, initial 4-CP concentration, and pH on 4-CP removal were evaluated. We observed that 4-CP was removed very rapidly when the HDC reaction was induced by Pd/GO and Pd/rGO. The granulation of Pd/rGO using sand was also investigated as a way to facilitate the separation of the catalyst from the treated aqueous solution after use, which is to improve practicality and effectiveness of the use of Pd catalysts with graphene-based support materials in an HDC system. The granulated catalyst (Pd/rGOSC) was employed in a column to induce HDC in a continuous flow reaction, leading to the successful removal of most 4-CP after 48 h. The reaction mechanisms were also determined based on the oxidation state of Pd, which was observed using X-ray photoelectron spectroscopy. Based on the results as a whole, the proposed granulated catalyst has the potential to greatly enhance the practical applicability of HDC for water purification. Full article

Chlorodifluoromethane (R-22), the most abundant freon in the atmosphere, was subjected to successful hydrodechlorination in the presence of palladium supported on γ-alumina, at a relatively low reaction temperature (180 °C). The combination of catalytic actions of alumina (performing freon dismutation) and Pd nanoparticles (catalyzing C–Cl bond splitting in the presence of hydrogen) results in the transformation of freon into valuable, chlorine-free products: methane and fluoroform, the mixture of which is used in plasma etching of silicon and silicon nitride. Very highly metal dispersed Pt/Al₂O₃ catalysts, with metal particles of ~1.3 nm in size, are not as effective as Pd/Al₂O₃, resulting in only partial dechlorination. A long-term dechlorination screening (3–4 days) showed good catalytic stability of Pd/alumina catalysts. Full article

It is well known that the hydrodechlorination (HDC) of chlorinated aromatic contaminants in aqueous effluents enables a significant increase in biodegradability. HDC consumes a low quantity of reactants producing corresponding non-chlorinated and much more biodegradable organic compounds. Two commonly used precious metals free Al alloys (Raney Al-Ni and Devarda’s Al-Cu-Zn) were compared in reductive action in an alkaline aqueous solution. Raney Al-Ni alloy was examined as a universal and extremely effective HDC agent in a diluted aqueous NaOH solution. The robustness of Raney Al-Ni activity is illustrated in the case of HDC of polychlorinated aromatic compounds mixture in actual waste water. In contrast, Devarda’s Al-Cu-Zn alloy was approved as much less active for HDC of the tested chlorinated aromatic compounds, but with a surprisingly high selectivity on cleavage of C-Cl bonds in the meta and sometimes the ortho position in chlorinated aniline and sometimes chlorinated phenol structures. The reaction of both tested alloys with chlorinated aromatic compounds in the aqueous NaOH solution is accompanied by dissolution of aluminum. Dissolved Al in the alkaline HDC reaction mixture is very useful for subsequent treatment of HDC products by coagulation and flocculation of Al(OH)₃ caused by simple neutralization of the alkaline aqueous phase after the HDC reaction. Full article

Pd/MgO, Pd/MgF₂ and Pd/MgO-MgF₂ catalysts were investigated in the reaction of CCl₄ hydrodechlorination. All the catalysts deactivated in time on stream, but the degree of deactivation varied from catalyst to catalyst. The MgF₂-supported palladium with relatively large metal particles appeared the best catalyst, characterized by good activity and selectivity to C₂-C₅ hydrocarbons. Investigation of post-reaction catalyst samples allowed to find several details associated with the working state of hydrodechlorination catalysts. The role of support acidity was quite complex. On the one hand, a definite, although not very high Lewis acidity of MgF₂ is beneficial for shaping high activity of palladium catalysts. The MgO-MgF₂ support characterized by stronger Lewis acidity than MgF₂ contributes to very good catalytic activity for a relatively long reaction period (~5 h) but subsequent neutralization of stronger acid centers (by coking) eliminates them from the catalyst. On the other hand, the role of acidity evolution, which takes place when basic supports (like MgO) are chlorided during HdCl reactions, is difficult to assess because different events associated with distribution of chlorided support species, leading to partial or even full blocking of the surface of palladium, which plays the role of active component in HdCl reactions. Full article