Catalytic Hydrodehalogenation Research Articles

A low-coordinate platinum(0)-germylene for E–H bond activation and catalytic hydrodehalogenation

Pairing transition metals and heavier tetrylenes (Si, Ge, Sn, Pb) holds great potential for cooperative bond activation and catalysis. In this work, we investigate the reactivity of a low-coordinate Pt(0)/Ge(II) system that emerges from the reaction between the monoligated platinum(0) precursor [(PMe2ArDipp2)Pt(olefin)] with germylene dimer [ArDipp2GeCl]2 (where ArDipp2 = C6H3−2,6-(C6H3−2,6-iPr2)2). The resulting complex reveals ability for cooperative bond activation. Stoichiometric reactions with dihydrogen, water, methanol, ammonia and alkynes unveil the formation of Pt(II)-germyl compounds, characterized by distinct isomeric forms, whose flexibility derives from the particularly low-coordination. We explore its catalytic potential in the hydrodehalogenation of aliphatic, aromatic and main-group halides under dihydrogen atmosphere using both thermal and photochemical conditions, demonstrating promising conversions even for more challenging alkyl chlorides.

Catalytic hydrodehalogenation of iodinated contrast agents in drinking water: A kinetic study

The occurrence of iodinated contrast media (ICM) in water bodies represents a significant threat for public health due to their strong biochemical stability and recalcitrance to conventional water treatment systems. In this work, the feasibility of catalytic hydrodehalogenation (HDH) for the degradation of a representative group of ICMs (iohexol (IHX), iopromide (IPR), iopamidol (IPM) and diatrizoic acid (DIA)) is investigated. Complete degradation and deiodination of the isolated ICMs (1.6·10−2 mmol L−1) was achieved in less than 30 min in the presence of 0.25 g L−1 of different precious metal catalysts (Pd/Al2O3, Rh/Al2O3 and Pt/Al2O3) under ambient conditions, closing iodine balance by >95 %. Based on the identified reaction intermediates and final products, reaction mechanisms were accordingly proposed. A sequential reaction pathway was proposed for DIA removal, while reaction mechanisms encompassing both sequential and concerted reaction steps were proposed for the non-ionic ICMs (IHX, IPR, and IPM). Subsequent kinetic models, which successfully described experimental data, were developed from the elucidated reaction mechanisms, considering all species involved in the reaction. The versatility of the process was finally demonstrated in the treatment of real aqueous matrices (surface water and tap water) spiked with the ICMs mixture, except in the case of Pt/Al2O3 which suffered deactivation due to surface poisoning by halides. For this catalyst, kinetic constants ranged from 0.31 to 0.22 min−1 in deionized water, and from 0.04 to 0.08 min−1 in surface water as the reaction matrix. Among the tested catalysts, Pd/Al2O3 showed the highest activity and stability for the removal of ICMs.

Catalytic hydrodehalogenation activity and selectivity of polyiodinated phenolic disinfection byproducts at ambient conditions

Iodo-phenolic disinfection byproducts (DBPs) widely occur in disinfected water, posing potential risks to human health and the ecosystem as they possess higher toxicity than the bromo- and chloro-analogs. Herein, we elucidated the catalytic hydrodehalogenation (HDH) activity and selectivity of polyiodinated phenolic DBPs on supported noble metal catalysts at ambient conditions. Both 2,4,6-triiodophenol and 4-chloro-2,6-diiodophenol can be efficiently eliminated on Pd/TiO2 and Rh/TiO2 within 20 min, with Pd/TiO2 exhibiting higher turnover frequency. The HDH reactions proceeded in both stepwise and concerted pathways on Pd/TiO2, while they were dominantly stepwise on Rh/TiO2. Experimental results and theoretical calculations revealed that the HDH selectivity depends on the position and the bond energy of halo-substitutions. For the HDH of 2,4,6-triiodophenol, the para-substituted iodine was more favorable to be dehalogenated than the ortho-substituted ones due to the steric hindrance of the hydroxyl group. For the HDH of 4-chloro-2,6-diiodophenol, the ortho-substituted iodine was removed before the para-substituted chlorine as CI bond had higher reactivity than CCl bond. Significant catalyst deactivation was observed for the HDH of 4-chloro-2,6-diiodophenol on Pd/TiO2 due to iodine poisoning, resulting in 4-chlorophenol as the dominant product. In contrast, Rh/TiO2 can completely hydrodehalogenate 4-chloro-2,6-diiodophenol into cyclohexanone with little iodine poisoning. Our results suggest that HDH is an efficient process for abating iodo-phenolic DBPs. Rh/TiO2 is a more promising HDH catalyst for iodinated DBP removal than Pd/TiO2 with excellent resistance to iodine poisoning.

Degradation of pharmaceuticals and other emerging pollutants employing bi-metal catalysts/magnesium and/or (green) hydrogen in aqueous solution

Contaminations by pharmaceuticals, personal care products, and other emerging pollutants in water resources have become a seriously burgeoning issue of global concern in the first third of the twenty-first century. As societal reliance on pharmaceuticals continues to escalate, the inadvertent introduction of these substances into water reservoirs poses a consequential environmental threat. Therefore, the aim of this study was to investigate reductive degradation, particularly, catalytic hydrogenation regarding model pollutants such as diclofenac (DCF), ibuprofen (IBP), 17α-ethinylestradiol (EE2), or bisphenol-A (BPA), respectively, in aqueous solutions at lab scale. Iron bimetals (zero valent iron, ZVI, and copper, Cu, or nickel, Ni) as well as zero valent magnesium (Mg, ZVM) in combination with rhodium, Rh, or palladium, Pd, as hydrogenation catalysts (HK), were investigated. Studies were executed through various short-term batch experiments, with multiple sample collections, over a total range of 120 min. The results indicated that DCF was attenuated at over 90 % when exposed to Fe-Cu or a Fe-Ni bimetal (applied as a single model pollutant). However, when DCF was part of a mixture alongside with IBP, EE2, and BPA, the attenuation efficacy decreased to 79 % with Fe-Cu and 23 % with Fe-Ni. Conversely, both IBP and BPA exhibit notably low attenuation levels with both bimetals, less than 50 %, both deployed as single substances or in mixtures. No reaction (degradation) products could be identified employing LC-MS, but sometimes a release of the parent pollutant when applying an acetic acid buffer could be noted to a certain extent, suggesting adsorption processes on corrosion products such as iron hydroxide and/or oxides. Surprisingly, Mg in combination with Rh (Rh-HK) or Pd (Pd-HK) showed a significantly rapid decrease in the concentrations of DCF, EE2, and BPA, in part up to approximately 100 %, that is, within a few minutes only in part due to hydrogenation degradation reactions (related reaction products could actually be identified by LC-MS; adsorption processes were not observed here). Moreover, kinetic modeling of the DCF degradation with Mg-Rh-HK was conducted at different temperatures (15 °C, 20 °C, 25 °C, 35 °C) and varied initial concentrations (2.5 mg/L, 5.0 mg/L, 7.5 mg/L, 10.0 mg/L). The outcomes prove that the degradation of DCF at the Rh-HK’s surface followed a modified first-order kinetics, most probably by catalytic hydrodehalogenation and subsequent hydrogenation of the aromatic moieties (molecular hydrogen was provided by the corrosion of Mg). From the determined reaction rate constants at four different temperatures, the activation energy was estimated to be 59.6 kJ/mol by means of the Arrhenius equation what is in good agreement with similar results reported in the literature. This coupled hydrodehalogenation and hydrogenation approach may be upscaled into a new promising technical process for comprehensively removing such pharmaceuticals and similar pollutants in sewage plants in a single step, furthermore, even in combination with adsorption by activated carbon and/or ozonation which have already been established at some sewage plants in Switzerland and Germany recently.

Catalytic Hydrodehalogenation of Haloarenes: Electron Transfer Reactions and Related Transformations: a Review

Catalytic Hydrodehalogenation of Haloarenes: Electron Transfer Reactions and Related Transformations: a Review

Heterogeneous catalytic reactions of in-situ generated bromide ions via hydrodehalogenation of tetrabromobisphenol A in advanced oxidation processes over palladium nanoparticles

Herein, we report a novel and efficient approach for degrading tetrabromobisphenol A (TBBPA) via catalytic hydrodehalogenation (HDH) and advanced oxidation processes (AOP). Using heterogeneous catalytic HDH of TBBPA over palladium nanoparticles (Pd NPs) achieves the in-situ generation of bromide ions (Br-), which effectively accelerate and reinforce the degradation of debromination intermediates during peroxymonosulfate-based AOP. The conversion of TBBPA to bisphenol A (BPA) by the HDH process reaches up to 99.9% debromination efficiency in 1 h under near-neutral condition, along with the removal of 99.4% BPA in 15 min during the AOP. Further studies show that free bromine and 1O2 produced by in-situ generated Br- reacting with peroxymonosulfate are the most effective reactive species for promoting the BPA degradation. Sustainability footprint analysis reveals considerable stability and high sustainable footprint of the integrated process during long-term operation. This work provides a promising strategy to elimination of bromine organic pollutants in water treatment.

Catalytic Hydrodehalogenation of Haloarenes with Hydrogen and Hydrogen-Containing Compounds: A Review

Catalytic Hydrodehalogenation of Haloarenes with Hydrogen and Hydrogen-Containing Compounds: A Review

Catalytic hydrodehalogenation of the flame retardant tetrabromobisphenol A by alumina-supported Pd, Rh and Pt catalysts

Tetrabromobisphenol A (TBBPA) is one of the most used BFRs, being characterized by a strong persistence and leading to negative effects on both the environment and human health. The aim of this work is to evaluate the feasibility of aqueous-phase catalytic hydrodehalogenation (HDH) for the fast and environmentally-friendly degradation of the brominated flame retardant TBBPA. Pd, Rh, and Pt on alumina commercial catalysts (1% wt.) were tested and reactions were performed under ambient operating conditions. TBBPA (1 mg L−1) was completely removed in short reaction times (< 5 min) using the Pd catalyst while longer reaction times were required in the case of Rh and Pt catalysts as active phase. Furthermore, although TBBPA suffered a strong adsorption on the catalyst surface, both adsorbed and free molecules reacted. Bromine balance was closed (> 95%) in 15 min using Pd/Al2O3. Nevertheless, employing Rh and Pt alumina-supported catalysts debromination of TBBPA increased progressively requiring much longer times and only 83% and 78% debromination yields were achieved after 2 h reaction, respectively. Bisphenol A (BPA), a well-known endocrine disruptor, was generated as reaction intermediate but it was further hydrogenated with both Pd and Rh catalysts, whereas it remained as reaction product with the Pt catalyst. A series reaction pathway considering both hydrodebromination and hydrogenation steps was proposed based on the obtained results. The experimental data obtained with the Pd/Al2O3 catalyst were successfully described by a pseudo-first order kinetic model, obtaining an apparent activation energy of 36 kJ mol−1. Notably, this catalyst showed a reasonable stability after three consecutive HDH runs.

Front Cover: The Electronic Properties of Ni(PNN) Pincer Complexes Modulate Activity in Catalytic Hydrodehalogenation Reactions (Eur. J. Inorg. Chem. 47/2020)

The Front Cover shows that nickel complexes of new PNN pincer ligands are excellent catalysts for the hydrodehalogenation of aryl halides (bromonaphthalene being shown here) when using NaBH4 as base and hydride source. The potency of the catalysts is enhanced by incorporating an electron-donating group at a para-aryl position of the diarylamido anchor, which becomes evident in comparative studies with less receptive aryl halide substrates. More information can be found in the Full Paper by D. Wang and J. R. Gardinier.

The Electronic Properties of Ni(PNN) Pincer Complexes Modulate Activity in Catalytic Hydrodehalogenation Reactions

Three chloronickel(II) complexes of PNN‐ pincer ligands with pyrazolyl and diphenylphosphino donors appended to different arms of diarylamido anchors were prepared and fully characterized. The three derivatives (1‐OMe, 1‐Me, 1‐CF3) differ only by the identity of the para‐aryl substituent on the pyrazolyl arm with 1‐OMe being 310 mV easier to oxidize than 1‐CF3. All three complexes are competent catalysts for hydrodehalogenation reactions of 1‐bromooctane and a variety of aryl halides in dimethylacetamide using NaBH4 as both base and hydride source. Comparative studies using diverse substrates showed that catalytic activity correlates with electron donor properties; 1‐OMe was superior to the other two. Deuterium labeling studies verified NaBD4 as the deuteride source and excluded solvent‐assisted radical pathways.

Complete dehalogenation of bromochloroacetic acid by liquid phase catalytic hydrogenation over Pd/CeO2 catalysts

Bromochloroacetic acid is classified as one of the typical disinfection byproducts (DBPs). In this work, supported palladium catalysts on different supports (CeO2, Al2O3, SiO2 and activated carbon (AC)) (labelled as Pd/support) were synthesized via the deposition-precipitation method (D-P method) and their activities for the complete dehalogenation of bromochloroacetic acid by liquid phase catalytic hydrogenation were evaluated. Comprehensive characterizations of the catalysts were conducted by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), point of zero charge (PZC), X-ray photoelectron spectroscopy (XPS) and CO chemisorption. Results indicated that the PZCs of the supports varied with each other. The stronger Pd-support interaction and higher Pd dispersion of Pd/CeO2 and Pd/Al2O3 than those of Pd/AC and Pd/SiO2 were confirmed by X-ray photoelectron spectroscopy and CO chemisorption. Pd/CeO2 had a higher ratio of positively charged Pd to metallic Pd (Pdn+/Pd0) than Pd/Al2O3 and Pd/AC due to a stronger metal-support interaction. Accordingly, a negligible bromochloroacetic acid conversion was observed on Pd/SiO2, whereas bromochloroacetic acid was found to be readily decomposed on Pd/CeO2, Pd/Al2O3 and Pd/AC. However, the dechlorination reaction could not further proceed on Pd/Al2O3 and Pd/AC catalysts after the bromine functionality was removed from bromochloroacetic acid. A complete dehalogenation of bromochloroacetic acid occurred only on Pd/CeO2. Furthermore, the dechlorination rate constants of monochloroacetic acid and bromochloroacetic acid over Pd(1.40)/CeO2 were 0.018 and 0.031 min−1 respectively, confirming an induced synergistic effect due to the existence of bromine atoms. It was worth noting that a stepwise-concerted pathway was verified during the liquid phase catalytic hydrodehalogenation of bromochloroacetic acid.

A Comparative Study of Carbon Supports for Pd/Au Nanoparticle-Based Catalysts

Abstract Carbon materials are promising supports for heterogeneous catalysis compared to oxide supports, such as titania, alumina, mesoporous silica, and hydrotalcite, because of their stability and relative chemical inertness. Additionally, the unique surface structures of carbon supports help control the growth, aggregation, and uniformity of the catalytic nanoparticles (NPs) hybridized with them. However, the effect of carbon supports on these NP catalysts is not well understood, affecting the optimization of this type of catalysts. In this study, palladium-gold (Pd/Au) carbon composites were systematically investigated, and the most favorable carbon support was identified. Carbon-supported Pd/Au NPs have often been favored for catalytic hydrodehalogenation (HDH) of volatile organic compounds. Hence, this study uses trichloroethylene (TCE) as model contaminant to investigate the effects of four types of carbon supports—granular activated carbon (GAC), carbon black, graphite, and graphite nanoplates—on the formation of catalytic Pd/Au NPs and their correlations to HDH reactions. Each support was chosen based on a desirable quality: GAC has a large surface area and substantial absorption capabilities, carbon black has a high surface-area-to-volume ratio and good chemical stability, graphite is the most stable form of carbon with a layered structure and thermal stability, and graphite nanoplates have large surface areas with structural stability. Characterizations of these Pd/Au-carbon composites show different NP sizes on each support, with GAC and carbon black generating smaller NPs. The HDH results suggest GAC, carbon black, and graphite nanoplates composites generate fast reaction rates. However, when comparing particle size and surface area, Pd/Au-GAC composites generate the fastest TCE degradation, providing a bigger boost to HDH rates than other types of carbon supports. More advantageously, GAC is widely available commercially with relatively low cost, and its high surface area is enabled by its high porosity, making GAC the preferred carbon support for Pd/Au NP catalyst mass production.

The Recycling of Spent Ammonia Borane with HBr/AlBr3 and Other HX/AlX3 -Based Schemes.

Although the development and application of a BNHx -waste recycling process is one of the major prerequisites for the use of ammonia borane as hydrogen source material, most research groups in the field have focused on AB hydrogen release and only few groups have worked on the development of energetically viable recycling schemes. In our work we target the development of a closed recycling process containing three desired steps: superacid break-up of the BNHx -waste, catalytic hydrodehalogenation of the generated boron halide, and base-exchange between Et3 NBH3 and ammonia. Catalytic hydrodehalogenation provides a convenient means to generate B-H bonds using molecular hydrogen, avoiding potentially energetically expensive reduction reagents.

Synthesis of hydrofluorocyclopentanes by vapor-phase catalytic hydrodehalogenation

Hydrofluorocyclopentanes (c5-HFCs) were prepared by gas-phase hydrodehalogenation of chlorofluorocyclopentenes (c5-CFOs) over various noble metals catalysts. The activity of the catalysts followed the order Pd > Pt > Rh > Ru, and the halogen atom on the C(sp2) atom exhibited stronger reactivity than the halogen on the C(sp3) atom. Possible mechanisms of the gas-phase hydrodehalogenation of c5-CFOs re proposed herein.

Comparative study on catalytic hydrodehalogenation of halogenated aromatic compounds over Pd/C and Raney Ni catalysts.

Catalytic hydrodehalogenation (HDH) has proved to be an efficient approach to dispose halogenated aromatic compounds (HACs). Liquid-phase HDH of single and mixed halobenzenes/4-halophenols with H2 over 5% Pd/C and Raney Ni catalyst are investigated and compared. For liquid-phase HDH of single HACs, hydrogenolytic scission reactivity of C-X bonds decreases in order of C-Br > C-Cl > C-I > C-F over Pd/C catalyst, and in order of C-I > C-Br > C-Cl > C-F over Raney Ni catalyst. To clarify the reason why hydrogenolytic scission reactivity of C-X bonds over Pd/C and Raney Ni catalysts exhibits different trends, liquid-phase HDH of mixed HACs over Pd/C and Raney Ni catalysts were studied, and catalysts are characterized by SEM, EDX, and XRD techniques. It was found that the high adsorption of iodoarenes on Pd/C catalyst caused the HDH reactivity of iodoarenes to be lower than that of chloroarenes and bromoarenes in the HDH of single HACs. Moreover, the adsorption of in situ produced iodine ion (I−) to catalyst surface would result in the decline of catalytic activity, which might be the main reason why the HDH reactivity of HACs in the presence of NaI is rather low.

Soil treatment by solvent extraction and catalytic hydrodehalogenation

We investigated the extraction of halogenated hydrophobic organic contaminants (HHOCS) from soil, and the subsequent catalytic hydrodehalogenation of extracted HHOCs. We used water/ethanol mixtures as the solvent and pentachlorophenol and 1,2,4,5-tetrachlorobenzene as target contaminants. The efficiency of extraction improved with increasing contact time and/or increasing ethanol fraction in the solvent, but, surprisingly, did not improve with increasing solvent volume. Tetrachlorobenzene extracted from the contaminated soil could be dehalogenated catalytically, with no apparent interference or inhibition caused by the extraction process. This suggests that a proposed new remediation technology (called remedial extraction and catalytic hydrodehalogenation, or REACH) should be technically viable.

A Self‐Contained Regeneration Scheme for Spent Ammonia Borane Based on the Catalytic Hydrodechlorination of BCl3

Recycling: A self-contained procedure for the recycling of BNH-waste, based on the three major steps: polymer break-up, amine supported catalytic hydrodehalogenation of boron halogens, and the base exchange in borane amine adducts, is developed (see picture). Beyond the original task of recycling spent ammonia borane, the process provides a new means to produce borohydride species efficiently, by the direct use of molecular hydrogen.

Liquid Phase Hydrodechlorination of Chlorobenzene over Bimetallic Supported Zirconia Catalyst

Mesoporous zirconia was prepared by the surfactant-assisted route, using cetyltrimethylammonium bromide as cationic surfactant. The synthesized zirconia was employed as support for copper and nickel bimetallic catalysts in the hydrodehalogenation reaction of chlorobenzenes and substituted chlorobenzenes at room temperature. The catalysts were characterized by nitrogen adsorption–desorption, X-ray powder diffraction, Fourier-transfer infrared spectroscopy (FTIR), transmittance electron micrograph (TEM), UV–vis diffuse reflectance spectroscopy (UV–vis DRS), temperature programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS). The nitrogen adsorption–desorption studies revealed that the modified samples retain the mesoporosity. TEM studies showed uniform distribution of metals having 5–10 nm particles size on the support surface. The bimetallic catalyst exhibited a higher H2 chemisorption capacity relative to monometallic catalysts. For catalytic hydrodehalogenation of chlorobenzene, bimetallic...

Fe0-based trimetallic systems for the removal of aqueous diclofenac: Mechanism and kinetics

The performance of amended micrometric iron particles (Fe0) in trimetallic systems for the removal of aqueous diclofenac (DF) was investigated. Tested additive metals were Pd, Cu and Ni. Trimetallic systems were shown superior to Fe0 for aqueous DF removal both under oxic and anoxic conditions. The extent of DF removal varied with (i) the combination of the additives, (ii) the order of plating on Fe0 surface, (iii) the availability of dissolved oxygen and (iv) the presence of MnO2. In comparison with previous results for bimetallic systems: (i) DF reduction products were observed under anoxic conditions for all trimetallic systems and only in some bimetallic systems; and (ii) under oxic conditions, DF reaction products were only observed in CuPdFe system. This was accredited to the intrinsic and electronic properties of the involved metals. Rapid DF removal was mainly attributed to the capacity of additive metals to accelerate Fe0 corrosion and thus producing more atomic hydrogen within the porous iron oxide layers. This promoted catalytic hydrodehalogenation was clearly apparent in systems where reductive transformation products were identified (e.g. PdCuFe). Recycling experiments using PdCuFe showed a continuous reactivity even after 4 successive cycles under anoxic conditions, however, under oxic conditions, a serious reactivity loss was noticed.

Remediation of contaminated soil by solvent extraction and catalytic hydrodehalogenation: Semicontinuous process with solvent recycle

AbstractHalogenated hydrophobic organic contaminants (HHOCs), such as chlorinated benzenes and polychlorinated biphenyls, are common soil contaminants. We propose a new method for treating soils contaminated by HHOCs by extracting the contaminants with a solvent, then destroying the contaminants catalytically, enabling the solvent to be reused. Here, we report on the assessment of this technology at the lab scale, operating in a semicontinuous mode where the solvent is recycled in a closed loop. The solvent employed was a mixture of water and ethanol, the catalyst was 1% palladium (Pd) on porous alumina, and hydrogen gas was used as the reductant. We tested the process on two soils: Texas sandy loam contaminated in the laboratory, and Florida sandy clay loam collected from a contaminated field site. The technology worked successfully on the Texas soil: over 90% of the contamination (pentachlorophenol and 1,2,4,5‐tetrachlorobenzene) could be extracted and destroyed within 1 week using a solvent flow rate of 0.005 L/(min‐kg soil) and a residence time of ∼3.5 min in the catalytic reactor. Seven batches of soil were treated (one week each) without needing to replace the solvent. Catalyst activity decreased over time but was recovered by cleaning the catalyst with a dilute solution of hypochlorite. However, the process was unsuccessful at treating the Florida soil because of rapid catalyst deactivation. We believe that the proposed technology (called remedial extraction and catalytic hydrodehalogenation, or REACH) is a promising “green” technology if we can protect the catalyst from deactivation; possible methods for achieving this are discussed. © 2010 American Institute of Chemical Engineers Environ Prog, 2010.