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Borohydride and metallic copper as a robust dehalogenation system: Selectivity assessment and system optimization
Ali Shee1, Frank-Dieter Kopinke1, Katrin Mackenzie1
1Helmholtz Centre for Environmental Research - UFZ, Department of Environmental Engineering, Permoserstraße 15, D-04318 Leipzig, Germany.
The Science of the Total Environment
|December 13, 2021
Summary
Copper-borohydride reduction system (CBRS) effectively treats halogenated organic compounds (HOCs) in water. This study shows CBRS is a cost-effective and potent alternative to noble metal catalysts for hydrodechlorination.
Area of Science:
- Environmental Chemistry
- Catalysis
- Water Treatment
Background:
- Hydrodechlorination (HDC) using noble metals is effective for removing halogenated organic compounds (HOCs) from water.
- Copper (Cu) offers a cheaper and more stable alternative to noble metal catalysts like Palladium (Pd), Rhodium (Rh), and Platinum (Pt).
- The copper-borohydride reduction system (CBRS) utilizes copper and borohydride (BH4-) as a reductant for HOC treatment.
Purpose of the Study:
- To evaluate the hydrodechlorination (HDC) efficacy of the copper-borohydride reduction system (CBRS) for saturated aliphatic HOCs.
- To determine product selectivities during the reduction of CCl3-R compounds (R = H, F, Cl, Br, CH3).
- To compare CBRS with conventional noble metal catalysts for treating α-substituted haloalkanes.
Main Methods:
- The HDC ability of CBRS was assessed by analyzing product selectivities during the reduction of various CCl3-R compounds.
- Reaction conditions, including solution composition and reducing agents (BH4-, H2), were varied to study their effect on product selectivity.
- Optimization of a secondary reduction step was performed to manage halogenated by-products using increased catalyst dose, silver (Ag), and vitamin B12.
Main Results:
- For CHCl3, CH2Cl2, and CHCl2-CH3, HDC predominantly occurred via α-elimination, yielding CH4 (84-85 mol-%) and C2H6 (70-72 mol-%).
- Stepwise hydrogenolysis dominated for CCl4, CBrCl3, CFCl3, and CCl3-CH3, forming recalcitrant CH2Cl-R intermediates (50-72 mol-%).
- Product selectivities were found to be substrate-specific, not significantly influenced by reaction conditions or reductant type.
Conclusions:
- The copper-borohydride reduction system (CBRS) is a potent and cost-effective alternative to noble metal catalysts for hydrodechlorination of α-substituted haloalkanes.
- CBRS demonstrates good performance, although halogenated by-products necessitate optimization of a secondary reduction step.
- The study recommends CBRS as a preferred agent for treating heavily contaminated waters with α-substituted haloalkanes.
Keywords:
BorohydrideCopper catalystsHalogenated organic compoundsProduct selectivity patternsReduction processesMore Related Videos
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