Helmholtz Centre for Environmental Research - UFZ, Department of Environmental Engineering, Permoserstraße 15, D-04318 Leipzig, Germany.
Helmholtz Centre for Environmental Research - UFZ, Department of Environmental Engineering, Permoserstraße 15, D-04318 Leipzig, Germany.
Sci Total Environ. 2022 Mar 1;810:152065. doi: 10.1016/j.scitotenv.2021.152065. Epub 2021 Dec 8.
Hydrodechlorination (HDC) using noble-metal catalysts in the presence of H-donors is a promising tool for the treatment of water contaminated by halogenated organic compounds (HOCs). Cu is an attractive alternative catalyst to noble metals since it is cheaper than Pd, Rh, or Pt and more stable against deactivation. Cu with borohydride (BH) as reductant (copper-borohydride reduction system; CBRS) was applied here for the treatment of saturated aliphatic HOCs. The HDC ability of CBRS was evaluated based upon product selectivities during reduction of CCl-R compounds (R = H, F, Cl, Br, and CH). For CHCl, CHCl, and CHCl-CH, the dechlorination reaction proceeds predominantly via α-elimination with initial product selectivities to CH and CH of 84-85 mol-% and 70-72 mol-%. For CCl, CBrCl, CFCl and CCl-CH, stepwise hydrogenolysis dominates. CHCl-R compounds are formed as recalcitrant intermediates with initial selectivities of 50-72 mol-%, whereas CH and CH are minor products with 16-35 mol-% and 30-35 mol-%. The effect of reaction conditions on product selectivities were investigated for CHCl as target. Solution composition, variation of reducing agents (BH, H* from H) and increase of electron pressure (electric potential at Cu electrode and Fe as support) did not have marked influence on the selectivities (ratio of CH : CHCl). Product selectivities for reduction of CCl-R compounds were found to be substrate-specific rather than reductant-specific. Since the formation of halogenated by-products could not be avoided, transformation via a second reduction step was optimized by higher catalyst dose, addition of Ag, and vitamin B12 to the CBRS. Comparison between Pd and Cu based on costs, catalyst activities, selectivities, metal stability, and fate of halogenated by-products shows that the CBRS is a potent alternative to conventional HDC catalysts and can be recommended as 'agent of choice' for treatment of α-substituted haloalkanes in heavily contaminated waters.
在供氢体存在的情况下使用贵金属催化剂进行氢脱氯（HDC）是处理含卤有机化合物（HOCs）污染水的一种很有前途的方法。与 Pd、Rh 或 Pt 相比，Cu 作为催化剂更便宜，而且失活稳定性更高，因此是贵金属的一种有吸引力的替代品。本文采用硼氢化氢（BH）作为还原剂（铜-硼氢化还原体系；CBRS）来处理饱和脂肪族 HOCs。根据 CCl-R 化合物（R = H、F、Cl、Br 和 CH）还原过程中的产物选择性来评估 CBRS 的 HDC 能力。对于 CHCl、CHCl 和 CHCl-CH，脱氯反应主要通过 α-消除进行，初始产物对 CH 和 CH 的选择性分别为 84-85 mol-%和 70-72 mol-%。对于 CCl、CBrCl、CFCl 和 CCl-CH，逐步氢解占主导地位。CHCl-R 化合物作为难降解中间体形成，初始选择性为 50-72 mol-%，而 CH 和 CH 则是次要产物，选择性分别为 16-35 mol-%和 30-35 mol-%。考察了反应条件对 CHCl 目标产物选择性的影响。溶液组成、还原剂（BH、H*来自 H）的变化和电子压力（Cu 电极和 Fe 作为载体的电势）的增加对选择性（CH：CHCl 比值）没有显著影响。发现 CCl-R 化合物还原的产物选择性是底物特异性的，而不是还原剂特异性的。由于无法避免卤代副产物的形成，因此通过增加催化剂剂量、向 CBRS 中添加 Ag 和维生素 B12 来优化第二步还原的转化。基于成本、催化剂活性、选择性、金属稳定性和卤代副产物的命运，将 Pd 和 Cu 进行比较表明，CBRS 是传统 HDC 催化剂的有力替代品，可以推荐为处理高污染水中α取代卤代烷的“首选试剂”。
