负载型纳米Pd／Fe对氯代烃脱氯机理研究

Dechlorination Mechanisms of Chlorinated Hydrocarbons by Supported Nanoscale Pd/Fe

采用实验室制备的负载型纳米Pd/Fe对几种常见的挥发性氯代烃:四氯乙烯(PCE)、三氯乙烯(TCE)、1,1-二氯乙烯(1,1-DCE)、氯乙烯(VC)和林丹(-γHCH)进行了还原脱氯研究.负载型纳米Pd/Fe对PCE、TCE、1,1-DCE、VC和-γHCH的还原脱氯符合准一级反应动力学方程,其反应速率常数分别为2.79 h-1、2.35 h-1、1.12 h-1、2.14 h-1和4.02 h-1.氯代烃降解过程中几乎没有中间产物生成,终产物主要为C2H6和C2H4,如对TCE进行降解时,生成的C2H6和C2H4分别占总碳质量比的70%和10%.采用暴露在空气中24 h的负载型纳米Pd/Fe对PCE进行脱氯,8次循环后仍能对PCE快速完全降解,表明负载型纳米Pd/Fe的稳定性能良好.以-γHCH为目标污染物对负载型纳米Pd/Fe的反应持久性进行了研究,200 h后负载型纳米Pd/Fe的反应性没有明显降低,表明负载型纳米Pd/Fe反应持久性能良好.温度对负载型纳米Pd/Fe的脱氯反应影响较大,测得各氯代烃脱氯反应的活化能均高于29 kJ.mol-1.对PCE、TCE进行了脱氯动力学模拟,模拟结果与试验数据基本吻合,表明负载型纳米Pd/Fe对氯代烃的脱氯,是连串、平行及多步骤反应的结合.

Some volatile chlorinated hydrocarbons such as VC,1,1-DCE,TCE,PCE, γ-HCH,were dechlorinated by synthesized supported nanoscale Pd/Fe.The dechlorination reactions of PCE,TCE,1,1-DCE,VC,γ-HCH follow the pseudo-frist order kinetics equations with the kobs of 2.79 h^-1,2.35 h^-1,1.12 h^-1,2.14 h^-1 and 4.02 h^-1 respectively.Little or no medial products were detected and the main end products were C2H6 and C2H4 during the dechlorination of VC,1,1-DCE, TCE,PCE.The total carbon ratio of C2H6 and C2H4 were 70% and 10% respectively during the dechlorination of TCE.The supported nanoscale Pd/Fe particles after exposed to air for 24 h were used for 8 cycle experiments and the results indicate that the particles have favorable stability.The reactivity has no obvious decrease after 200 hours＇ successive dechlorination experiments of γ-HCH which indicates that the particles represent good durability.The reaction activation energy of all the chlorinated hydrocarbons are bigger than 29kJ·mol^-1 which shows that the surface-chemical reaction rather than diffusion is the rate-limiting step in the metal-mediated dechlorination process.A consistence between the experimental data and simulated curves indicates that the muti-step reaction pathways proposed offer a better explanation of the reaction mechanisms than sequential hydrogenolysis reactions in the transformation of chlorinated hydrocarbons by supported nanoscale Pd/Fe.