Acta Phys. -Chim. Sin. ›› 2021, Vol. 37 ›› Issue (5): 2007089.doi: 10.3866/PKU.WHXB202007089

Special Issue: CO2 Reduction

• ARTICLE • Previous Articles     Next Articles

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)

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