【作者】 梁秋霞；

【导师】 李小年； 王丽丽；

【作者基本信息】 浙江工业大学 ， 工业催化， 2008， 博士

【摘要】 为了研究Pd/C催化剂制备过程中前驱体的吸附行为及Pd粒径的生长过程,制备可控尺寸的Pd/C催化剂,本论文使用硝酸、氢氧化钠、氨水预处理以及高温热处理等方法对活性炭进行改性,以H₂PdCl₄为前驱体采用浸渍法制备了一系列的Pd/C催化剂。在催化剂浸渍过程中,提出采用一种新的H₂PdCl₄测定方法—Na₂S滴定法,对Pd前驱体在活性炭载体上的平衡吸附量（EPU,Pd precursorequilibrium uptake）进行了测定。实验结果表明影响EPU值的主要因素是活性炭的PZC值（point-of-zero-charge）。Pd前驱体在活性炭上的吸附态则通过H₂-TPR、XPS等方法进行了研究,研究结果表明含氧基团在载体表面的含量及分布情况（以总酸密度DTA表征,density of totalacidity）,会影响Pd在载体表面的吸附态。Pd/C催化剂的Pd粒径由TEM法测得,将所得Pd粒径与PZC、EPU及DTA值进行关联之后发现,PZC及EPU值与Pd粒径之间并无直接对应关系,影响浸渍过程中Pd粒径的主要因素为载体的DTA值。进一步,本论文通过研究前驱体加入方式、pH调节及催化剂还原等步骤对Pd粒径的影响,确定了浸渍法制备Pd/C催化剂过程中Pd颗粒的生长过程,在此基础上制备了一系列可控尺寸的Pd/C催化剂,并将其应用于硝基苯加氢和3,4-二氯硝基苯加氢反应,都取得了较好的结果。该研究为有针对性地根据不同反应体系的特点制备可控尺寸的活性炭负载型铂族金属催化剂提供了一定的理论指导,改善了完全由实验室评价结果选择催化剂制备条件的传统方法。更多还原

【Abstract】 In order to prepare size-assembled Pd/C catalyst, investigations of Pd precursor adsorption behavior and the growth process of Pd particle size during Pd/C catalyst preparation were investigated. HNO₃, NaOH and NH₃·H₂O solutions were used for the pretreatment of activated carbon supports, and also high temperature treatment was performed for some of the carbon samples. A series of Pd/C catalysts were prepared by impregnation method using H₂PdCl₄ as precursor and the pretreated carbon as supports.During the impregnation process of Pd/C preparation, a new method Na₂S titration was proposed for the determination of Pd precursor equilibrium uptake （EPU） on the carbon surface. Adsorption experimental results indicated that Pd precursor equilibrium uptake is mainly influenced by PZC （point-of-zero-charge） value of the activated carbon. Adsorption state of Pd precursor on the surface of activated carbon was determined by H₂-TPR and XPS analysis. The results obtained suggested that Pd adsorption state is influenced by the content and distribution of surface oxygen-containing groups on the surface of activated carbon.Pd particle size of Pd/C catalyst is characterized by XRD and TEM analysis. Pd particle size of Pd/C catalyst is not highly dependent upon the PZC or EPU value, while the DTA value used to describe the content of surface acidic oxygen-containing groups and their distribution is found to be the most important factor that influences Pd particle size formed during the impregnation process of Pd/C preparation. Conclusively, Pd particle size is mainly influenced by the DTA value of the activated carbon via the altering of Pd⁰ nucleation and H₂PdCl₄ precursor diffusion rates. Although pH altering step and the reduction of Pd/C can also influence the Pd particle size, the most important factor is the Pd⁰ particles formed in the impregnation step. Furthermore, a series of particle size-assembled Pd/C catalysts were prepared for the hydrogenation of nitrobenzene and 3,4-dichloronitrobenzene, and high conversions and selectivities were obtained.更多还原