物理化学学报 >> 2019, Vol. 35 >> Issue (4): 431-441.doi: 10.3866/PKU.WHXB201805211

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Ga2O3改性Cu/SiO2催化剂降低水蒸气催化重整产物中CO选择性

黄静静1,蔡金孟1,马奎1,丁彤1,田野1,张静2,李新刚1,*()   

  1. 1 天津大学化工学院,天津化学化工协同创新中心,天津市应用催化科学与工程重点实验室,天津 300354
    2 中国科学院,北京高能物理研究所,北京同步辐射装置,北京 100049
  • 收稿日期:2018-03-26 发布日期:2018-09-13
  • 通讯作者: 李新刚 E-mail:xingang_li@tju.edu.cn
  • 基金资助:
    国家自然科学基金(21476159);国家自然科学基金(21476160);天津市自然科学基金(15JCZDJC37400);天津市自然科学基金(15JCYBJC23000)

Ga2O3-Modified Cu/SiO2 Catalysts with Low CO Selectivity for Catalytic Steam Reforming

Jingjing HUANG1,Jinmeng CAI1,Kui MA1,Tong DING1,Ye TIAN1,Jing ZHANG2,Xingang LI1,*()   

  1. 1 Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin Key Laboratory of Applied Catalysis Science and Engineering, School of Chemical Engineering & Technology, Tianjin University, Tianjin 300354, P. R. China
    2 Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, P. R. China
  • Received:2018-03-26 Published:2018-09-13
  • Contact: Xingang LI E-mail:xingang_li@tju.edu.cn
  • Supported by:
    the National Natural Science Foundation of China(21476159);the National Natural Science Foundation of China(21476160);the Natural Science Foundation of Tianjin, China(15JCZDJC37400);the Natural Science Foundation of Tianjin, China(15JCYBJC23000)

摘要:

采用蒸氨法制备的xGa-Cu/SiO2催化剂可以同时产生Cu0和Cu+物种,加入Ga后催化剂的二甲醚水蒸气重整反应活性和选择性都有很大程度的提高,其中5Ga-Cu/SiO2催化剂在380 ℃时的二甲醚转化率为99.8%,CO选择性为4.8%。通过透射电子显微镜(TEM),氢气-程序升温还原(H2-TPR),N2O滴定和X射线光电子能谱(XPS)结果发现,Ga与Cu物种之间的相互作用,一方面可以提高Cu物种的分散度,另一方面可以促进Cu+的形成。通过改变Ga负载量可以调变Cu+/(Cu0 + Cu+)的比例,氢气的时空收率结果表明,Ga通过调变Cu+/(Cu0 + Cu+)影响催化活性,并且当Cu+/(Cu0 + Cu+) = 0.5时,氢气时空收率达到最大值为5.02 mol·g-1·h-1。程序升温表面反应(TPSR)结果表明,Ga通过促进水气变换反应提高反应产物CO2选择性。

关键词: 水蒸气重整, 二甲醚, Cu/SiO2, Ga2O3, 选择性

Abstract:

Dimethyl ether (DME) is considered a promising energy source and clean fuel for the next generation, with its high hydrogen content, and non-toxicity compared with methanol. In addition, it is easy to store and transport. DME steam reforming (SR) has received considerable attention for its applicability in the production of hydrogen for fuel cell applications. Generally, DME SR consists of two steps: DME hydrolysis and methanol SR. DME hydrolysis often occurs on an acidic catalyst, such as γ-Al2O3. Methanol SR in Cu-based catalysts requires both Cu0 and Cu+ as the active sites; moreover, the relative ratios of Cu0 and Cu+ can influence the catalytic performance. In addition, the byproduct of CO also commonly exists in DME SR, and a small amount of CO can poison Pt electrodes of fuel cells. Therefore, it is necessary to reduce the concentration of the generated CO in DME SR. Herein, using an ammonia-evaporation method, we synthesized a Cu/SiO2 catalyst, which can simultaneously generate the dual copper species of Cu0 and Cu+ by reduction. After modification with Ga2O3, the xGa-Cu/SiO2 catalysts show much improved catalytic activity and decreased CO selectivity. The Cu/SiO2 catalyst shows a DME conversion of 90.7% and CO selectivity of 11.5% at 380 ℃. The 5Ga-Cu/SiO2 catalyst, with a loading amount of Ga2O3 of 5% (w, based on the weight of Cu), shows the best performance, with a DME conversion of 99.8% and CO selectivity of 4.8% under the same conditions. The measurement of apparent activation energies shows that the addition of Ga2O3 cannot change the reaction path. By multiple characterization methods, we demonstrated that the improved performance can be ascribed to the following two aspects. First, our characterization results show that the loaded Ga2O3 is highly dispersed on the Cu/SiO2 catalyst, which can increase the interaction between Ga and Cu species. This can not only improve the dispersion of copper species (Cu0 and Cu+) on the catalysts, but can also adjust the ratios of Cu+/(Cu0 + Cu+). The H2 production rate shows a typical volcano curve owing to the ratio of Cu+/(Cu0 + Cu+), and reaches a maximum of 5.02 mol·g-1·h-1 at Cu+/(Cu0 + Cu+) = 0.5 for the 5Ga-Cu/SiO2 catalyst. We conclude that the interaction between Ga and Cu species and the synergistic effect between Cu0 and Cu+ result in the promoted catalytic activity for DME SR. Second, by using a temperature-programmed surface reaction (TPSR), we showed that the addition of Ga2O3 can efficiently promote the water–gas shift reaction, thereby reducing the CO selectivity in DME SR. Thus, Ga2O3 suppresses the generation of CO, leading to the low CO selectivity and high CO2 selectivity. In summary, the Ga2O3-modified Cu/SiO2 catalyst yields reformates with low CO selectivity and high catalytic activity for DME SR. Our work provides a novel approach to designing a highly efficient Cu-based catalyst for catalytic SR systems.

Key words: Steam reforming, Dimethyl ether, Cu/SiO2, Ga2O3, Selectivity

MSC2000: 

  • O643