Co改性的Pd/C催化剂在转移加氢中的应用研究

Cobalt Modified Pd/C Catalyst for Tansfer Hydrogenation

通过调整Co和Pd的浸渍顺序制备了不同的钴改性的Pd/C催化剂,考察了催化剂在3,5-二羟基苯甲酸转移加氢制备3,5-二氧代环己烷羧酸反应中的活性。确认先浸渍钴后浸渍钯、并在300℃以氢气还原得到的Co-Pd/C催化剂具有最佳活性,反应转化率和选择性分别达到94.6%和99.5%。对该催化剂以BET、TPR、XRD、SEM、TEM、XPS等手段进行了表征。结果表明,先浸渍的钴占据了活性炭的微孔使最可几孔径由2.72nm增大为3.32nm,并且与一些对反应不利的官能团作用,使后浸渍的钯主要分布在催化剂的大孔中,避免了过多深度加氢副产物的生成。催化剂活性组分为零价的钯,其平均粒径约10nm,以有利于转移加氢的聚集态存在,使催化剂获得了较高的活性和选择性。

Different cobalt-modified Pd/C （Co-Pd/C） catalysts were prepared by adjusting impregnation order of Co and Pd. The activities of these catalysts were investigated through the transfer hydrogenation of 3,5-dihydroxybenzoic acid to 3,5-dioxocyclohexane carboxylic acid. The results show that the catalyst prepared by impregnating firstly with Co then following with Pd provides the best activity, and this catalyst needs to be reduced with hydrogen at 300℃ before using. The conversion ratio and selectivity of this catalyst can reach 94.6% and 99.5%, respectively. The Co-Pd/C catalysts were characterized by BET, TPR, XRD, SEM, TEM and XPS, respectively. The results indicate that the Co impregnated firstly on the active carbon fills the micro pores of the active carbon and acts with the disadvantageous functional groups on the surface of the active carbon, which changes the most probable pore diameter of the active carbon from 2.72 nm to 3.32 nm. It makes the latterly impregnated Pd distribute in the macro pores of the catalyst, and prevents deep hydrogenation. The active substance of the catalyst is zeo-valent Pd （Pd0）, and the particle diameter of Pd0 is about 10 nm. This state of Pd on the catalyst is fit for transfer hydrogenation, which makes the catalyst behave with high activity and high selectivity.