Copper oxide nanoparticles confined in TiO2 nanotubes for the water–gas shift reaction: promotional effect of potassium

Previous work showed that the copper oxide nanoparticles confined in titania nanotubes (Cu-in-TiO2NT) can effectively enhance the water–gas shift (WGS) activity. The WGS activity is directly related to the concentration of active copper species and oxygen vacancies (Ov). The addition of potassium is found to enhance WGS activity of copper catalysts to some extent. Herein, the K-promoted copper oxide (2 wt% Cu) nanoparticles confined in TiO2 nanotubes catalysts (Cu-in-K/TiO2NT) with different potassium contents were synthesized and investigated for the WGS reaction. The K-promoted catalysts exhibit the enhanced WGS activity. Especially, the Cu-in-K20/TiO2NT with the molar ratio of K/Cu = 20 displays twofold higher WGS activity compared with the Cu-in-TiO2NT. XRD, Raman, XPS, H2-TPR and in situ DRIFTS have verified that the addition of appropriate potassium can make active copper species bound with oxygen of the TiO2, leading to a partial reduction of TiO2 to TiO2-x, which is beneficial to form Cu–Ov–Ti site for the WGS reaction.