催化学报 ›› 2017, Vol. 38 ›› Issue (9): 1540-1548.DOI: 10.1016/S1872-2067(17)62847-X

• 论文 • 上一篇    下一篇

Cu分隔开的Pd单原子用于乙炔选择加氢:Cu担载量的影响

裴广贤a,b, 刘晓艳a, 柴梦倩a,b, 王爱琴a, 张涛a   

  1. a 中国科学院大连化学物理研究所, 辽宁大连 116023;
    b 中国科学院大学, 北京 100049
  • 收稿日期:2017-03-31 修回日期:2017-04-30 出版日期:2017-09-18 发布日期:2017-09-06
  • 通讯作者: 刘晓艳, 张涛
  • 基金资助:

    国家自然科学基金(21303194,21476227,21522608,21690084);中国科学院青年促进会(2014163);科技部国家重点研发计划"纳米科技"重点专项(2016YFA0202801);中科院战略性先导科技专项(XDB17020100);辽宁省科技部(2015020086-101).

Isolation of Pd atoms by Cu for semi-hydrogenation of acetylene:Effects of Cu loading

Guangxian Peia,b, Xiaoyan Liua, Mengqian Chaia,b, Aiqin Wanga, Tao Zhanga   

  1. a State Key Laboratory of Catalysis, Collaborative Innovation Center of Chemistry for Energy Materials(iChEM), Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, Liaoning, China;
    b University of Chinese Academy of Sciences, Beijing 100049, China
  • Received:2017-03-31 Revised:2017-04-30 Online:2017-09-18 Published:2017-09-06
  • Contact: 10.1016/S1872-2067(17)62847-X
  • Supported by:

    This work was supported by the National Natural Science Foundation of China (21303194, 21476227, 21522608 and 21690084), Youth Innovation Promotion Association of the Chinese Academy of Sciences (2014163), the National Key Projects for Fundamental Research and Development of China (2016YFA0202801), the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB17020100), and the department of sci-ence and technology of Liaoning province under contract of 2015020086-101.

摘要:

大量乙烯中少量乙炔的去除是化工生产中的重要过程之一,理想途径是将其选择加氢生成乙烯.负载型Pd催化剂因具有很高的乙炔转化率而被广泛用于该过程,但乙烯选择性很低,同时会使原料气中的乙烯被加氢,造成原料气的浪费.采用其它元素对Pd纳米粒子表面修饰,覆盖部分活性位,可以在一定程度上提高乙烯选择性,但是会大大降低Pd的利用率.因此,制备兼具高活性和高选择性且经济实用的催化剂,仍是这一过程亟待解决的主要问题之一.我们的前期工作中,将Pd与IB族金属(Au,Ag,Cu)分别结合制备得到了一系列含Pd的合金单原子催化剂(SAC),发现它们在大量乙烯存在条件下的乙炔选择加氢反应中表现出优异的催化性能.其中,Pd的用量仅为ppm级别,大大提高了Pd的利用率.作为IB族最为廉价的金属,Pd与Cu形成的合金SAC在提高Pd原子利用率的同时,能够进一步降低催化剂的经济成本.然而,当形成合金SAC时,Cu/Pd原子比例的极限值仍然不确定.
本文通过固定Pd的担载量,采用简单的等体积共浸渍的方法,制备了一系列不同Cu/Pd原子比例的氧化硅负载的双金属催化剂.首先,我们采用程序升温还原(TPR)和X射线衍射(XRD)对催化剂的还原能力和双金属纳米粒子的尺寸进行了考察.进一步,采用X射线吸收光谱(XAS,包括EXAFS和XANES)对双金属催化剂中Pd的配位环境进行了分析.最后,结合它们在大量乙烯存在条件下的乙炔选择加氢反应中的催化性能,对形成合金SAC时Cu/Pd原子比例进行了讨论.
TPR结果显示,Cu与Pd结合时会促进双金属纳米粒子的还原.XRD结果表明,随着Cu含量的降低,双金属纳米粒子的尺寸明显减小.XANES结果证实,当Pd与Cu结合时,Pd会带有部分负电荷,这也与Pd的电负性大于Cu相一致.通过对EXAFS拟合结果进行分析,我们发现当Cu/Pd的原子比例≥ 40/1时,Pd原子可以被Cu原子完全分隔开,形成含Pd的合金SAC,使其在大量乙烯存在条件下的乙炔选择加氢反应中表现出优异的催化性能.通过对还原温度的考察,我们发现还原温度由250℃升高到400℃时,对同一催化剂的催化性能影响不大;EXAFS拟合结果显示,对比分别经过250和400℃还原后的催化剂,Pd的配位环境变化不明显,这可能是导致催化性能相似的主要原因.

关键词: 铜, 钯, 单原子催化剂, X射线吸收光谱, 乙炔加氢, 大量乙烯

Abstract:

Cu-alloyed Pd single-atom catalysts exhibit excellent catalytic performance for the semi-hydrogenation of acetylene; however, the limit of the Cu/Pd atomic ratio for forming the al-loyed Pd single-atom catalyst is ambiguous. Herein, silica-supported Cu-Pd bimetallic catalysts with fixed Pd content and varied Cu loadings were synthesized using an incipient wetness co-impregnation method. The X-ray absorption spectroscopy results indicated that Pd formed an alloy with Cu after reduction at 250℃ and that the Pd atoms were completely isolated by Cu for Cu/Pd atomic ratios ≥ 40/1. Notably, increasing the reduction temperature from 250 to 400℃ hardly affected the catalytic performances of the Cu-Pd/SiO2 catalysts. This finding can be attribut-ed to the similar chemical environments of Pd demonstrated by the X-ray absorption spectroscopy results.

Key words: Copper, Palladium, Single-atom catalyst, X-ray absorption spectroscopy, Acetylene hydrogenation, Excess ethylene