Al2O3负载Pd催化剂对溴氯代乙酸的催化加氢脱卤研究
Catalytic hydrodehalogenation of bromochloroacetic acid on alumina supported palladium catalysts
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摘要: 分别以氧化铝、氧化硅和多壁碳纳米管为载体,采用沉淀-沉积法制备负载型Pd催化剂.采用透射电镜(TEM)、X射线衍射(XRD)、电感耦合等离子体发射光谱(ICP-AES)、X射线光电子能谱(XPS)等手段对材料进行表征,并对溴氯代乙酸(BCAA)的液相催化加氢脱卤反应进行了研究.结果表明,由于Pd/Al2O3催化剂具有较高的等电点,因此相对于Pd/CNT、Pd/SiO2在BCAA的加氢脱卤反应中具有更高的活性.以Pd/Al2O3为目标催化剂,对BCAA的加氢脱卤展开研究,发现催化活性随Pd的负载量的增加而提高.当反应物的初始浓度为0.1 mmol·L-1,pH值为5.6,Pd (1.39)/Al2O3用量为25 mg·L-1时,BCAA在20 min时可以实现完全脱溴并在反应2 h后脱氯达60.5%.另外,pH的升高不利于脱卤反应的进行.当反应物的浓度从0.05 mmol·L-1提高到0.4 mmol·L-1时,反应初活性从1.55 mmol·L-1 min-1 gCat-1提高到8.37 mmol·L-1 min-1 gCat-1.进一步通过拟合Langumir-Hinshelwood模型,相关系数达到0.97,说明BCAA的加氢脱卤是吸附控制机制.催化过程中溴氯代乙酸的脱溴和脱氯具有协同作用,反应最终生成乙酸.Abstract: Pd catalysts supported on alumina, silica and multi-walled carbon nanotubes were prepared by the precipitation-deposition method. The catalysts were characterized by TEM, XRD, ICP-AES and XPS, and the catalytic hydrodehalogenation of bromochloroacetic acid (BCAA) was studied. The results show that the Pd/Al2O3 catalyst had a higher catalytic activity in the hydrodehalogenation reaction of BCAA than Pd/CNT and Pd/SiO2. Afterwards, the hydrodehalogenation of BCAA catalyzed by Pd/Al2O3 was studied further, and it was found that the reactivity increased with the increase of Pd loading. When the initial concentration of the reactant was 0.1 mmol·L-1, the pH was 5.6, and the amount of Pd(1.39)/Al2O3 was 25 mg·L-1, BCAA achieved complete debromination in 20 min and 60.5% dechlorination after 2 h of reaction. Under alkaline conditions, the increase of pH was not conducive to the dehalogenation. When the concentration of the reactant was increased from 0.05 mmol·L-1 to 0.4 mmol·L-1, the initial activity of the reaction increased from 1.55 mmol·L-1 min-1 gCat-1to 8.37 mmol·L-1 min-1 gCat-1. Further, by fitting the Langumir-Hinshelwood model, the correlation coefficient reached 0.97, which indicates that the hydrodehalogenation of BCAA is an adsorption controlled mechanism. The debromination and dechlorination of bromochloroacetic acid in the catalytic process had a synergistic effect, and the reaction finally produced acetic acid.
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