Liquid phase hydrodechlorination of chlorophenols at lower temperature on a novel Pd catalyst

Liquid-phase hydrodechlorination of trichloroethylene driven by nascent H2 under an open system: Hydrogenation activity, solvent effect and sulfur poisoning

Hydrodechlorination is a promising technology for the remediation of water body contaminated with trichloroethylene (TCE). In this work, the liquid-phase hydrogenation of TCE by Raney Ni (R-Ni) and Pd/C under an open system have been studied, in which nascent H₂ (Nas-H₂) generated in situ from the cathode acted as a hydrogen source. Experimental results showed that TCE was completely eliminate from the solution through the synergistic effects of hydrodechlorination and air flotation due to the formation of continuous micro/nano-sized Nas-H₂ bubbles from the cathode. Furthermore, the effects of inorganic anions and organic solvents on R-Ni and Pd/C hydrogenation activity were investigated, respectively. The results showed that NO₃^- and acetonitrile can form a competitive reaction with TCE; Sulfur with lone-pair electrons will cause irreversible poisoning to these two catalysts, and have a stronger inhibitory effect on Pd/C. This work helps to realize the separation of volatile halogenated compounds from water environment and provides certain data support for the choice of catalyst in the actual liquid-phase hydrogenation system.

Efficient Degradation of 2,4-Dichlorophenol on Activation of Peroxymonosulfate Mediated by MnO2

Sulfate radical based-advanced oxidation process has received increasing interest in the remediation of wastewater and contaminated soil. In this study, degradation of 2, 4-dichlorophenol (2, 4-DCP) was investigated over peroxymonosulfate (PMS) activation by MnO₂, which was prepared by liquid-phase oxidation method. The prepared MnO₂ was characterized by transition electron microscopy, X-ray diffraction, N₂ adsorption-desorption, and X-ray photoelectron spectroscopy. Characterization results showed that α-MnO₂ exhibited the highest surface area and Mn (III) content. The PMS activation by MnO₂ in 2, 4-DCP degradation followed the order of α-MnO₂ >  γ-MnO₂ > β-MnO₂, which is dependent on the properties of MnO₂ including crystal structure, surface area and Mn (III) content. Influences of initial concentration of 2, 4-DCP, PMS and MnO₂ dosage, pH and co-existing inorganic ions on the degradation were examined. Electron paramagnetic resonance (EPR) and quenching experiments with ethanol and tert-butanol suggested that sulfate radicals were the dominant radicals in the process. Findings in this study indicated that α-MnO₂ was an attractive catalyst for activation of PMS to degrade 2, 4-DCP in aqueous solution.

Hydrodechlorination of 4-Chlorophenol on Pd-Fe Catalysts on Mesoporous ZrO2SiO2 Support

A mesoporous support based on silica and zirconia (ZS) was used to prepare monometallic 1 wt% Pd/ZS, 10 wt% Fe/ZS, and bimetallic FePd/ZS catalysts. The catalysts were characterized by TPR-H₂, XRD, SEM-EDS, TEM, AAS, and DRIFT spectroscopy of adsorbed CO after H₂ reduction in situ and tested in hydrodechlorination of environmental pollutant 4-chlorophelol in aqueous solution at 30 °C. The bimetallic catalyst demonstrated an excellent activity, selectivity to phenol and stability in 10 consecutive runs. FePd/ZS has exceptional reducibility due to the high dispersion of palladium and strong interaction between FeOx and palladium, confirmed by TPR-H₂, DRIFT spectroscopy, XRD, and TEM. Its reduction occurs during short-time treatment with hydrogen in an aqueous solution at RT. The Pd/ZS was more resistant to reduction but can be activated by aqueous phenol solution and H₂. The study by DRIFT spectroscopy of CO adsorbed on Pd/ZS reduced in harsh (H₂, 330 °C), medium (H₂, 200 °C) and mild conditions (H₂ + aqueous solution of phenol) helped to identify the reasons of the reducing action of phenol solution. It was found that phenol provided fast transformation of Pd⁺ to Pd⁰. Pd/ZS also can serve as an active and stable catalyst for 4-PhCl transformation to phenol after proper reduction.

One-Pot Aqueous and Template-Free Synthesis of Mesoporous Polymeric Resins

This work explores the novel one-pot aqueous phase synthesis of mesoporous phenolic-hyperbranched polyethyleneimine resins without the use of a template, and their utility as heterogeneous catalysts in batch reactors and continuous microreactors. Catalyst surface areas of up to 432 m2/g were achieved with a uniform Pd distribution and an interconnected, highly porous, network structure, confirmed through Brunauer–Emmett–Teller (BET) surface area measurements, scanning electron microscopes (SEM), X-Ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscopy (TEM), and Energy-dispersive X-ray spectroscopy (EDS). The heterogeneous catalysts achieved a maximum 98.98 ± 1% conversion in batch Suzuki couplings, with conversions being dependent upon reaction conditions, reactant chemistries, Pd loading and catalyst surface area. The catalysts were shown to be recyclable with only a marginal loss in conversion achieved after five runs. Up to 62 ± 5% and 46.5 ± 8% conversions at 0.2 mL/s and 0.4 mL/s flow rates, respectively, were achieved in a continuous microreactor. Understanding the mechanism of action of this mesoporous resin is a future research area, which could help expand the application vistas for this catalyst platform.

Palladium Supported on Titanium Carbide: A Highly Efficient, Durable, and Recyclable Bifunctional Catalyst for the Transformation of 4-Chlorophenol and 4-Nitrophenol

Developing highly efficient and recyclable catalysts for the transformation of toxic organic contaminates still remains a challenge. Herein, Titanium Carbide (Ti₃C₂) MXene modified by alkali treatment process was selected as a support (designated as alk-Ti₃C₂X₂, where X represents the surface terminations) for the synthesis of Pd/alk-Ti₃C₂X₂. Results show that the alkali treatment leads to the increase of surface area and surface oxygen-containing groups of Ti₃C₂X₂, thereby facilitating the dispersion and stabilization of Pd species on the surface of alk-Ti₃C₂X₂. The Pd/alk-Ti₃C₂X₂ catalyst shows excellent catalytic activity for the hydrodechlorination of 4-chlorophenol and the hydrogenation of 4-nitrophenol in aqueous solution at 25 °C and hydrogen balloon pressure. High initial reaction rates of 216.6 and 126.3 min⁻¹·gpd−1 are observed for the hydrodechlorination of 4-chlorophenol and hydrogenation of 4-nitrophenol, respectively. Most importantly, Pd/alk-Ti₃C₂X₂ exhibits excellent stability and recyclability in both reactions without any promoters. The superior property of Pd/alk-Ti₃C₂X₂ makes it as a potential material for practical applications.

Catalysis of the hydrodechlorination of 4-chlorophenol and the reduction of 4-nitrophenol by Pd/Fe3O4@C

A recyclable and efficient magnetic core–shell Pd/Fe₃O₄@C nanocatalyst is applied in the HDC of 4-CP and hydrogenation of 4-NP.

Molecularly Imprinted Polymers Based Electrochemical Sensor for 2,4-Dichlorophenol Determination

A molecularly imprinted polymers based electrochemical sensor was fabricated by electropolymerizing pyrrole on a Fe₃O₄ nanoparticle modified glassy carbon electrode. The sensor showed highly catalytic ability for the oxidation of 2,4-dichlorophenol (2,4-DCP). Square wave voltammetry was used for the determination of 2,4-DCP. The oxidation peak currents were proportional to the concentrations of 2,4-DCP in the range of 0.04 to 2.0 µM, with a detection limit of 0.01 µM. The proposed sensor was successfully applied for the determination of 2,4-DCP in water samples giving satisfactory recoveries.

Effective hydrodechlorination of 4-chlorophenol catalysed by magnetic palladium/reduced graphene oxide under mild conditions

Magnetic palladium/reduced graphene oxide nanocomposites (Pd/rGO-Fe₃O₄) were prepared by depositing Pd nanoparticles on an rGO-Fe₃O₄ magnetic support.

In situ synthesis of Au–Pd bimetallic nanoparticles on amine-functionalized SiO2 for the aqueous-phase hydrodechlorination of chlorobenzene

The homogeneous Au–Pd NPs have been prepared through a facile in situ reduction method. The optimal AuPd_1.0/SiO₂ catalyst could complete the conversion of chlorobenzene due to the high dispersion and modified electronic properties of Pd.

Complete dechlorination of 2,4-dichlorophenol in aqueous solution on palladium/polymeric pyrrole-cetyl trimethyl ammonium bromide/foam-nickel composite electrode

The electrochemically reductive dechlorination of 2,4-dichlorophenol (2,4-DCP) in aqueous solution on palladium/polymeric pyrrole-cetyl trimethyl ammonium bromide/foam-nickel electrode (Pd/PPy-CTAB/foam-Ni electrode) was investigated in this paper. Pd/PPy-CTAB/foam-Ni electrode was prepared and characterized by cyclic voltammetry (CV), scanning electron microscope (SEM), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) adsorption and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The influences of some experimental factors such as the dechlorination current, dechlorination time and the initial pH on the removal efficiency and the current efficiency of 2,4-DCP dechlorination on Pd/PPy-CTAB/foam-Ni electrode were studied. Complete removal of 2,4-DCP was achieved and the current efficiency of 47.4% could be obtained under the conditions of the initial pH of 2.2, the dechlorination current of 5 mA and the dechlorination time of 50 min when the initial 2,4-DCP concentration was 100 mg L(-1). The analysis of high performance liquid chromatography (HPLC) identified that the intermediate products were 2-chlorophenol (2-CP) and 4-chlorophenol (4-CP). The final products were mainly phenol. Its further reduction product cyclohexanone was also detected. The electrocatalytic dechlorination pathways of 2,4-DCP on Pd/PPy-CTAB/foam-Ni electrode were discussed. The stability of the electrode was favorable that it could keep dechlorination efficiency at 100% after having been reused 10 times. Results revealed that the stable prepared Pd/PPy-CTAB/foam-Ni electrode presented a good application prospect in dechlorination process with high effectiveness and low cost.

Ordered mesoporous phenolic resins: highly versatile and ultra stable support materials

Ordered mesoporous phenolic resins and carbons - an advanced class of ultra-stable mesoporous materials - offer potential applications in the field of catalysis, electrodes and adsorbents. This review gives an extensive overview of the main principles and the recent progress made in the synthesis of these innovative materials using the soft-template method. Furthermore, the versatility towards functionalization and the incorporation of hetero-atoms in the organic framework of the mesoporous resins and carbons are considered. Finally, the broad range of potential applications is discussed and future perspectives in the field of mesoporous polymers and carbons are given.