负载型纳米Pd/C的尺寸可控制备及其2,3,6-三氯吡啶加氢性能

Size-controlled Preparation of AC Supported Nano Pd Catalyst and Its Hydrogenation of 2,3,6-trichloropyridine

在催化剂制备过程中引入氨羧络合剂(氨三乙酸三钠,NTA),通过配位作用稳定并保护Pd粒子,得到纳米Pd/C催化剂,研究了氨三乙酸三钠引入量对Pd/C催化剂结构的影响。通过X射线衍射(XRD)、X射线光电子能谱(XPS)、透射电镜(TEM)及化学吸附(H_2-TPR)表征发现,与常规浸渍法制备的Pd/C催化剂相比,氨三乙酸三钠的引入能够有效减小Pd的平均粒径,并且通过调变氨三乙酸三钠的量可以获得Pd粒子不同大小的负载型Pd/C催化剂,随着氨三乙酸三钠引入量的增多(Pd摩尔含量的0.5、1、2倍),Pd粒径由5.7 nm减小至2.1 nm,但是继续增加氨三乙酸三钠的量(Pd摩尔含量的4倍),Pd粒径不再继续减小。当氨三乙酸三钠:Pd=1:1时,即Pd粒子大小约为4 nm时,催化剂获得了最佳催化反应性能,反应6 h原料全部转化,2,3-二氯吡啶的选择性可达76.86%。

Pd/C catalysts were prepared by introducing complexone （nitrilotriacetic acid trisodium salt, NTA） into Pd precursor solutions, and then Pd particles were stabilized by the coordination of Pd^2＋ and NTA. Catalysts were characterized by XRD, XPS, TEM and H2-TPR. Results show that compared with Pd/C catalyst prepared by an impregnation method, the average particle size of Pd could be effectively reduced by introducing NTA during preparation. Furthermore, Pd particles could be size-controlled by adjusting the amount of NTA. The average particle size of Pd is decreased from 5.7 nm to 2.1 nm by increasing NTA from 0.5 time to twice of Pd （molar ratio）, but Pd particle size does not continue to decrease by furthur increasing the amount of NTA. When the average particle size is 4 nm （NTA：Pd=1：1） the optimum catalytic performance is achieved, i.e. the conversion is 100% and selectivity of 2,3-dichloropyridine is up to 76.86% after 6 h of reaction.