浸渍法制备Pd／C催化剂过程中Pd前驱体的平衡吸附量与吸附态  

Equilibrium Uptake and Adsorption State of Pd Precursor in Preparation of Pd/C Catalyst by Impregnation

作　　者：梁秋霞[1] 马磊[1] 郑遗凡[1] 卢春山[1] 张群峰[1] 李小年[1] 

机构地区：[1]浙江工业大学工业催化研究所,绿色化学合成技术国家重点实验室培育基地,浙江杭州310032

出　　处：《催化学报》2008年第2期145-152,共8页

基　　金：浙江省科技计划项目(2004C21029,2005C11023-01)

摘　　要：使用不同浓度(0～67%)的硝酸对活性炭载体进行预处理,以H2PdCl4为前驱体,用浸渍法制备理论负载量为5%的Pd/C催化剂.浸渍过程中的吸附实验表明,Pd前驱体的平衡吸附量随预处理硝酸浓度的增加而逐渐减小,尤其是浓硝酸预处理的活性炭载体,其上仅有62.54%的Pd前驱体吸附,而37.46%的Pd前驱体仍在水浆液中.分析发现,Pd前驱体的平衡吸附量主要取决于活性炭的零电荷点,表面电荷模型能较好地描述Pd前驱体的吸附规律.当使用浓度≤5%的硝酸进行预处理时,Pd的粒径随硝酸浓度的增加而减小;当硝酸浓度继续增加时,Pd粒径急剧增大.Pd前驱体的平衡吸附量与Pd粒径的大小无直接关系,而Pd前驱体在活性炭表面上吸附物种及数量的不同也对Pd粒径的大小产生影响.活性炭表面基团的增加抑制了PdClyx-吸附物种的生成.当使用≤5%的硝酸处理活性炭时,Pd前驱体的吸附形态主要为PdClxy-和Pd0;当硝酸浓度>5%时,没有检测到PdClyx-的存在.A series of activated carbon used as supports were pretreated with different concentrations of HNO3. Pd/C catalysts were then prepared by impregnation using H2PdCl4 solution as the Pd precursor. The results of adsorption experiments in the impregnation process indicated that the equilibrium uptake of the Pd precursor on the surface of activated carbon decreased with increasing HNO3 concentration for the pretreatment. When undiluted HNO3 was used, only 62.54 % of Pd precursor was adsorbed on the surface of activated carbon, and about 37.46 % of Pd precursor was still reserved in the slurry. The Pd precursor equilibrium uptake was highly dependent upon the point-of-zero charge of the activated carbon. Compared with the surface oxygen anchoring mechanism, the surface charge model gives a better explanation of the adsorption experimental results. Pd particle size was initially decreased with increasing HNO3 concentration （≤5 % ） and then increased with further increasing HNO3 concentration （ 〉 10 % ）. No obvious correlation between the Pd precursor equilibrium uptake and the Pd particle size was found because the particle size of Pd was also affected by Pd precursor adsorption species and their amounts. Formation of PdClx^y- adsorption species was inhibited by the increase of oxygen-containing groups on the activated carbon surface. When a low HNO3 concentration （≤5 % ） was used for the pretreatment of activated carbon, PdClx^y- and Pd^0 were the main adsorption states of Pd precursor, whereas when the HNO3 concentration was high （〉5%）, PdClx^y- was not detected.

关 键 词：钯 活性炭 负载型催化剂 平衡吸附量 粒径 零电荷点 表面含氧基团 

分 类 号：O643.36[理学—物理化学]