物理化学学报 >> 2020, Vol. 36 >> Issue (11): 1911008.doi: 10.3866/PKU.WHXB201911008

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ZnO逆修饰小尺寸Cu/SiO2催化剂及其在CO2加氢制甲醇中的应用

吕翰林1, 胡兵2, 刘国亮2, 洪昕林2,*(), 庄林1,2,*()   

  1. 1 武汉大学高等研究院,武汉 430072
    2 武汉大学化学与分子科学学院,武汉 430072
  • 收稿日期:2019-11-04 发布日期:2020-01-06
  • 通讯作者: 洪昕林,庄林 E-mail:hongxl@whu.edu.cn;lzhuang@whu.edu.cn
  • 基金资助:
    国家自然科学基金(21872106);国家自然科学基金(21603244);中央高校基本科研业务费专项资金(2042019kf0019)

Inverse Decoration of ZnO on Small-Sized Cu/Sio2 with Controllable Cu-ZnO Interaction for CO2 Hydrogenation to Produce Methanol

Hanlin Lyu1, Bing Hu2, Guoliang Liu2, Xinlin Hong2,*(), Lin Zhuang1,2,*()   

  1. 1 Institute for Advanced Studies, Wuhan University, Wuhan 430072, P. R. China
    2 College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, P. R. China
  • Received:2019-11-04 Published:2020-01-06
  • Contact: Xinlin Hong,Lin Zhuang E-mail:hongxl@whu.edu.cn;lzhuang@whu.edu.cn
  • Supported by:
    the National Natural Science Foundation of China(21872106);the National Natural Science Foundation of China(21603244);the Fundamental Research Funds for the Central Universities, China(2042019kf0019)

摘要:

Cu-ZnO催化剂广泛应用于CO2还原制甲醇,但是如何构建具备强金属-载体相互作用、粒径可控的Cu-ZnO催化剂仍然富有挑战性。本文发展了一种利用高比表面硅酸铜前驱物合成小粒径且组分相互作用可控的Cu-ZnO/SiO2催化剂的方法,制备得到一系列ZnO含量不同的Cu-ZnO/SiO2催化剂,并对其CO2加氢制甲醇的催化活性进行系统考察。发现在523 K的条件下,甲醇选择性由未加入ZnO的20%提高至ZnO含量为14%时的67%。催化剂活性与ZnO含量之间呈现火山型关系,在ZnO含量为7%,温度为543 K,H2/CO2压力为4.5 MPa时,甲醇时空产率(STY)最优,为244 g·kg-1·h-1。此外,本文探究了催化剂中Cu与ZnO的协同效应,发现ZnO可以显著增强Cu的催化活性,但过量ZnO的引入会使Cu颗粒粒径增长,降低催化剂中的总反应位点数,进而影响催化剂催化活性。

关键词: CO2还原制甲醇, Cu-ZnO催化剂, 硅酸铜, Cu-ZnO协同效应

Abstract:

Cu-ZnO is broadly used as a catalyst in CO2 reduction to produce methanol, but fabricating small-sized Cu-ZnO catalysts with strong Cu-ZnO interactions remains a challenge. In this work, a simple, low-cost method is proposed to synthesize small-sized Cu-ZnO/SiO2 with high activity and controllable Cu-ZnO interactions derived from copper silicate nanotubes. A series of Cu-ZnO/SiO2 samples with different amounts of ZnO were prepared. The activities of the as-prepared catalysts for methanol synthesis were tested, and the results revealed a volcano relationship with the weight fraction of ZnO. At 523 K, the methanol selectivity increased from 20% to 67% when 14% ZnO was added to the Cu/SiO2 catalyst, while the conversion of CO2 increased first and then decreased with the addition of ZnO. The optimum space time yield (STY) of 244 g·kg-1·h-1 was obtained on C-SiO2-7%ZnO at 543 K under 4.5 MPa H2/CO2. Furthermore, the synergistic effect of Cu and ZnO was studied by high resolution transmission electron microscopy (HRTEM), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), in situ diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS), and temperature-programmed reduction (TPR) analyses. The HRTEM images showed that the Cu particles come in contact with ZnO more frequently with increased addition of ZnO, indicating that the catalysts with higher ZnO contents have a greater probability of formation of the Cu-ZnO interface, which promotes the catalytical activity of Cu-ZnO/SiO2. Meanwhile, the HRTEM images, XRD patterns, and TPR results showed that the addition of excess ZnO leads to an increase in the size of the Cu particles, which in turn decreases the total number of active sites and further degrades the activity of the catalysts. The activation energy (Ea) for methanol synthesis and reverse water gas shift (RWGS) was calculated based on the results of the catalytical test. With the addition of ZnO, Ea for methanol synthesis decreased from 72.5 to 34.8 kJ·mol-1, while that for RWGS increased from 61.3 to 102.7 kJ·mol-1, illustrating that ZnO promotes the synergistic effect of Cu-ZnO. The results of XPS and in situ DRIFTS showed that the amount of Cu+ species decreases with the addition of ZnO, indicating that the Cu-ZnO interface serves as the active site. The Cu surface area and the turnover frequency (TOF) of methanol were calculated based on the H2-TPR curves. The TOF of methanol on the Cu-ZnO/SiO2 catalysts at 543 K increased from 1.5 × 10-3 to 3.9 × 10-3 s-1 with the addition of ZnO, which further confirmed the promotion effect of the Cu-ZnO interface on the methanol synthesis. This study provides a method to construct Cu-ZnO interfaces based on copper silicate and to investigate the influence of ZnO on Cu-ZnO/SiO2 catalysts.

Key words: CO2 reduction to methanol, Cu-ZnO catalyst, Copper silicate, Cu-ZnO synergistic effect

MSC2000: 

  • O643