Catalytic hydrodechlorination of trichloroethylene in a novel NaOH/2-propanol/methanol/water system on ceria-supported Pd and Rh catalysts

Efficient hydrogenation of p-chlorophenol and Cr(VI) driven by hydrogen rich balls over Pd/C catalysts

Catalytic hydrogenation can selectively destabilize and detoxify specific contaminants in water. Herein, to explore safer and more efficient hydrogen sources, hydrogen rich balls (HRBs) were researched and applied for hydrogenating p-chlorophenol and Cr(VI) over Pd/C catalyst. The results showed that HRBs can realize the sustained release of H₂ by replacing the hydrogen in water, and generate the refined (micro/nano-sized) H₂ bubble, which effectively improves the adsorption and activation effectively of H₂ molecules on Pd/C catalyst, and the hydrogen atoms utilization efficiency during p-chlorophenol hydrodechlorination is as high as 3.5 %. Continuous flow experiments showed that rapid removal of p-chlorophenol with different concentrations could be achieved by adjusting the flow rate. Moreover, the high-toxic Cr(VI) was successfully reduced to the low-toxic Cr(III) in an appropriate pH range. This research is of far-reaching significance for realizing the detoxification of environmental pollutants and promoting the development of hydrogen economy.

Feasibility study on the electrochemical reductive decomposition of PFOA by a Rh/Ni cathode

The discharge of widely used per- and poly-fluorinated compounds (PFCs) leads to their environmental prevalence, bioaccumulation and biotoxicity; and attracts researches focusing on their treatment in wastewater. Electrochemical reductive treatment is a promising alternative due to its milder reaction conditions and easy operation. The feasibility of electrochemical reductive decomposition of PFOA using a Rh/Ni cathode was explored. The Rh/Ni cathode was fabricated by coating Rh³⁺ on Ni foil through electrodeposition. The Rh coating was primarily elemental and in a Rh(111) crystalline form. PFOA decomposition and defluorination were observed when using the Rh/Ni cathode where DMF was the solvent and the cathode potential was -1.25 V. A hydrodefluorination reaction was considered having occurred. Because possessing d electrons and empty d orbitals, the Rh coating enhanced PFOA adsorption onto the cathode surface and facilitated CF bond activation through Rh···F interactions. Moreover, the Rh(111) crystal helped chemisorb the generated H* and supply it participating in PFOA decomposition. With the continuous interaction of cathode-supplied electrons, CF bond would ultimately dissociate and transform to CH bond by H* substitution. Adding FeCp₂* as a supporting electrolyte enhanced PFOA decomposition by working as the shuttle facilitating PFOA migration to the cathode surface.

An efficient reduction of unsaturated bonds and halogen-containing groups by nascent hydrogen over Raney Ni catalyst

Presence of unsaturated bonds and halogen-containing groups is the most common characteristic of toxic and harmful environmental pollutants. Herein, catalytic hydrogenation was chosen as a water quality control method for such contaminants. Considering the safety, availability and activity of the hydrogen source, electrochemical in situ hydrogen generation was introduced. Under the combined action of Raney Ni (R-Ni) and nascent hydrogen (Nas-H₂), three compounds (50 mg L^-1, 90 ml), i.e., acrylamide, 2, 6-dibromo-4-nitrophenol and 2-chloro-4-fluorobenzonitrile achieved complete hydrogenation reduction in a short time. The improved system realized the quantitative consumption of hydrogen source and the efficient operation of hydrogenation reaction under mild conditions. Additionally, the alkaline environment formed by hydrogen evolution reaction (HER) avoided secondary pollution caused by catalyst dissolution. Atomic hydrogen (H·) produced from R-Ni and Nas-H₂ was the active free radical of the reaction. The hydrogenation activities of different functional groups were obtained according to the following order: Ph-NO₂ ＞ -C = C- ＞ Ph-C≡N ＞ Ph-Br ＞ Ph-Cl ＞ Ph-F. This work indicates that the catalytic hydrogenation system consisting of R-Ni and Nas-H₂ is a promising technology to reduce unsaturated bonds and halogen-containing groups.

Properties of Carbon-supported Precious Metals Catalysts under Reductive Treatment and Their Influence in the Hydrodechlorination of Dichloromethane

This study analyzes the effect of the reduction temperature on the properties of Rh, Pt and Pd catalysts supported on activated carbon and their performance in the hydrodechlorination (HDC) of dichloromethane (DCM). The reduction temperature plays an important role in the oxidation state, size and dispersion of the metallic phase. Pd is more prone to sintering, followed by Pt, while Rh is more resistant. The ratio of zero-valent to electro-deficient metal increases with the reduction temperature, with that effect being more remarkable for Pd and Pt. The higher resistance to sintering of Rh and the higher stability of electro-deficient species under thermal reductive treatment can be attributed to a stronger interaction with surface oxygen functionalities. Dechlorination activity and a TOF increase with reduction temperature (250–450 °C) occurred in the case of Pt/C catalyst, while a great decrease of both was observed for Pd/C, and no significant effect was found for Rh/C. Pt0 represents the main active species for HDC reaction in Pt/C. Therefore, increasing the relative amount of these species increased the TOF value, compensating for the loss of dispersion. In contrast, Pdn+ appears as the main active species in Pd/C and their relatively decreasing occurrence together with the significant decrease of metallic area reduces the HDC activity. Rh/C catalyst suffered only small changes in dispersion and metal oxidation state with the reduction temperature and thus this variable barely affected its HDC activity.