物理化学学报 >> 2021, Vol. 37 >> Issue (5): 2007089.doi: 10.3866/PKU.WHXB202007089

所属专题: CO2还原

论文 上一篇    下一篇

Cu@UiO-66衍生的Cu+-ZrO2界面位点用于高效催化CO2加氢制甲醇

王艳秋, 钟子欣, 刘唐康, 刘国亮(), 洪昕林()   

  • 收稿日期:2020-07-29 录用日期:2020-08-25 发布日期:2020-08-28
  • 通讯作者: 刘国亮,洪昕林 E-mail:liugl@whu.edu.cn;hongxl@whu.edu.cn
  • 基金资助:
    国家自然科学基金(21872106);中央高校基本科研业务费专项资金(2042019kf0019)

Cu@UiO-66 Derived Cu+-ZrO2 Interfacial Sites for Efficient CO2 Hydrogenation to Methanol

Yanqiu Wang, Zixin Zhong, Tangkang Liu, Guoliang Liu(), Xinlin Hong()   

  • Received:2020-07-29 Accepted:2020-08-25 Published:2020-08-28
  • Contact: Guoliang Liu,Xinlin Hong E-mail:liugl@whu.edu.cn;hongxl@whu.edu.cn
  • About author:Email: hongxl@whu.edu.cn (H.X.)
    Email: liugl@whu.edu.cn (L.G.), Tel.: +86-13476231209 (L.G.)
  • Supported by:
    the National Natural Science Foundation of China(21872106);the Fundamental Research Funds for the Central Universities, China(2042019kf0019)

摘要:

Cu/ZrO2催化剂可以有效地将CO2加氢转化为甲醇,其中Cu-ZrO2界面在该反应中起着关键作用。因此,通过控制活性金属的尺寸和使用多孔载体,最大限度地增加Cu-ZrO2界面活性位点是开发理想催化剂的有效策略。MOF因其丰富的孔道结构和成分的可调性是一种理想的载体材料。其中UiO-66是一种以Zr为金属中心,对苯二甲酸(H2BDC)为有机配体的刚性金属有机骨架材料,具有良好的水热稳定性和化学稳定性。在此,我们使用UiO-66作为ZrO2的前驱体,将Cu纳米颗粒限制在UiO-66的孔隙/缺陷内构建了一种Cu/ZrO2纳米复合催化剂在CO2加氢制甲醇反应中具有很高的反应活性。催化剂在空气氛围中适当的温度下煅烧后可以产生大量的活性界面。通过调节煅烧温度和活性金属尺寸,活性界面可以得到优化。此外,TEM结果证明了CO2加氢制甲醇后Cu-ZrO2界面仍然存在,说明活性界面的稳定性。考察了金属Cu组分含量以及煅烧温度对催化剂的结构以及加氢活性的影响得到了最优催化剂。在280 ℃,4.5 MPa的反应条件下,CZ-0.5-400催化剂具有13.4 h-1最高的甲醇转换频率(TOF),此时二氧化碳的转化率为12.6%,甲醇的选择性为62.4%及其总时空收率(STY)达到587.8 g·kg-1·h-1 (按每千克催化剂计算,下同)。CO吸附的原位漫反射傅里叶变换红外光谱(DRIFTS)揭示了不可还原的Cu+物种在催化剂中占据了很大比例,XPS也证实了大量Cu+物种的存在。催化剂优异的反应活性来自于邻近ZrO2处形成的丰富的Cu+物种。而Cu+-ZrO2界面是甲醇合成反应的活性中心,可以作为桥梁将金属Cu物质解离的活性氢向ZrO2转运。此外,ZrO2的氧空穴促进了CO2的吸附和活化。ZrO2晶格中的Cu+和氧空穴是CO2加氢合成甲醇的活性位点。反应前后催化剂的XRD图谱以及TOS测试反映了催化剂的稳定性。此外,原位漫反射傅里叶变换红外光谱(DRIFTS)和程序升温表面反应-质谱(TPSR-MS)揭示了二氧化碳加氢制甲醇的反应机理,该反应遵循了甲酸盐为中间体的反应路径。

关键词: CO2加氢, 甲醇合成, Cu+-ZrO2界面, Cu/ZrO2催化剂, UiO-66

Abstract:

Cu/ZrO2 catalysts have demonstrated effective in hydrogenation of CO2 to methanol, during which the Cu-ZrO2 interface plays a key role. Thus, maximizing the number of Cu-ZrO2 interface active sites is an effective strategy to develop ideal catalysts. This can be achieved by controlling the active metal size and employing porous supports. Metal-organic frameworks (MOFs) are valid candidates because of their rich, open-framework structures and tunable compositions. UiO-66 is a rigid metal-organic skeleton material with excellent hydrothermal and chemical stability that comprises Zr as the metal center and terephthalic acid (H2BDC) as the organic ligand. Herein, porous UiO-66 was chosen as the ZrO2 precursor, which can confine Cu nanoparticles within its pores/defects. As a result, we constructed a Cu-ZrO2 nanocomposite catalyst with high activity for CO2 hydrogenation to methanol. Many active interfaces could form when the catalysts were calcined at a moderate temperature, and the active interface was optimized by adjusting the calcination temperature and active metal size. Furthermore, the Cu-ZrO2 interface remained after CO2 hydrogenation to methanol, as confirmed by transmission electron microscopy (TEM), demonstrating the stability of the active interface. The catalyst structure and hydrogenation activity were influenced by the content of the active component and the calcination temperature; therefore, these parameters were explored to obtain an optimized catalyst. At 280 ℃ and 4.5 MPa, the optimized CZ-0.5-400 catalyst gave the highest methanol turnover frequency (TOF) of 13.4 h-1 with a methanol space-time yield (STY) of 587.8 g·kg-1·h-1 (calculated per kilogram of catalyst, the same below), a CO2 conversion of 12.6%, and a methanol selectivity of 62.4%. In situ diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS) of CO adsorption over the optimized catalyst revealed a predominant, unreducible Cu+ species that was also identified by X-ray photoelectron spectroscopy (XPS). The favorable activity observed was due to this abundant Cu+ species coming from the Cu+-ZrO2 interface that served as the methanol synthesis active center and acted as a bridge for transporting hydrogen from the active Cu species to ZrO2. In addition, the oxygen vacancies of ZrO2 promoted the adsorption and activation of CO2. These vacancies and Cu+ trapped in the ZrO2 lattice are the active sites for methanol synthesis from CO2 hydrogenation. The X-ray diffraction (XRD) patterns of the catalyst before and after reaction revealed the stability of its structure, which was further verified by time-on-stream (TOS) tests. Furthermore, in situ DRIFTS and temperature-programmed surface reaction-mass spectroscopy (TPSR-MS) revealed the reaction mechanism of CO2 hydrogenation to methanol, which followed an HCOO-intermediated pathway.

Key words: CO2 hydrogenation, Methanol synthesis, Cu+-ZrO2 interfaces, Cu/ZrO2 catalysts, UiO-66

MSC2000: 

  • O643