制备条件对Pd/C催化剂活性相PdH_x的影响

Influence of Preparation Condition on the PdH_x Phase of Pd/C Catalyst

PdHx相是Pd/C催化剂中一种重要的活性物种。研究以浸渍-水合肼还原法制备出PdHx含量较高的Pd/C催化剂,通过XRD、XPS和TEM等表征方法研究了还原方式和条件及载体活性炭的预处理条件对催化剂中PdHx含量的影响,以无氢条件下的2,6-二甲基苯酚胺化法合成2,6-二甲基苯胺作为探针反应,验证了PdHx含量与催化活性的相关性。结果表明:以2.5%(wt)硝酸预处理的活性炭为载体,水合肼为还原剂,在40℃还原制得的催化剂具有较高的PdHx含量,以其为催化剂时原料的转化率和产品的选择性分别高达59.8%和87.3%。说明PdHx是该反应的活性相,其含量与载体预处理时的硝酸浓度密切相关。

PdHx phase is an important reactive species in the Pd/C catalyst. The Pd/C catalyst with high content of PdHx phase was controllably prepared by the impregnation-hydrazine hydrate reduction method, and the influences of reduction methods, reduction conditions and the pretreatment conditions of the activated carbon on the PdHx content were investigated by XRD, XPS and TEM. By using the amination of 2,6-dimethyl phenol in the absence of hydrogen as a probe reaction, the relationship between PdHx content and catalytic activity was also studied. The results show that the Pd/C catalyst with high amount of PdHx can be obtained by using activated carbon support pretreated with 2.5%（wt） HNO3 and reducing the catalyst with hydrazine hydrate as reductor at 40℃. And over this catalyst the conversion of 2,6-dimethylphenol and the selectivity for 2,6-dimethylaniline are as high as 59.8% and 87.3%, respectively. It shows that the PdHx is the reactive phase of amiation reaction and its content is closely related to the concentration of HNO3 in the pretreatment process.