Kim Y H, Carraway E R
Clemson University, Department of Environmental Toxicology, Clemson Institute of Environmental Toxicology, 509 Westinghouse Rd., Pendleton, SC 29670-0709, USA.
Environ Technol. 2002 Oct;23(10):1135-45. doi: 10.1080/09593332308618332.
The reductive dechlorination of tetrachloroethene (PCE) and trichloroethene (TCE) catalyzed by vitamin B12 was examined when zero valent metals (ZVMs) were used as bulk electron donors in batch reactors. UV-visible spectra showed that zinc reduces vitamin B12 Co(III) to vitamin B12 Co(I) through B12 Co(II) and iron reduces vitamin B12 Co(III) to vitamin B12 Co(II). Thus iron, the most popular ZVM reductant, does not have enough reduction potential toreduce vitamin B12 to the super-reduced vitamin B12(I), which has been shown to be an active species in reductive dechlorination. Dechlorination of PCE and TCE by iron and zinc in the presence of vitamin B12 showed that the zinc and vitamin B12 combination greatly enhances the reaction rates for both PCE and TCE, but iron and vitamin B12 result in an increase in reactivity only for PCE degradation, not for TCE degradation in comparison with metals only. This result indicates vitamin B12(I) is active towards both PCE and TCE degradation while vitamin B12(II) is active only towards PCE. Calculated activation energies for the dechlorination of PCE in the presence of Vitamin B12 showed that vitamin B12 lowered the activation energy about 40-60 kJ mol(-1) for both metals.
在间歇式反应器中，当使用零价金属（ZVMs）作为大量电子供体时，研究了维生素B12催化的四氯乙烯（PCE）和三氯乙烯（TCE）的还原脱氯反应。紫外可见光谱表明，锌通过维生素B12 Co（II）将维生素B12 Co（III）还原为维生素B12 Co（I），铁则将维生素B12 Co（III）还原为维生素B12 Co（II）。因此，最常用的ZVM还原剂铁，没有足够的还原电位将维生素B12还原为超还原态的维生素B12（I），而后者已被证明是还原脱氯反应中的活性物种。在维生素B12存在下，铁和锌对PCE和TCE的脱氯反应表明，锌与维生素B12的组合极大地提高了PCE和TCE的反应速率，但与仅使用金属相比，铁与维生素B12仅使PCE降解的反应活性增加，而对TCE降解没有影响。这一结果表明，维生素B12（I）对PCE和TCE的降解均有活性，而维生素B12（II）仅对PCE有活性。计算得出在维生素B12存在下PCE脱氯反应的活化能表明，维生素B12使两种金属的活化能降低了约40 - 60 kJ mol（-1）。
