Insight into the function of alkaline earth metal oxides as electron promoters for Au/TiO2 catalysts used in CO oxidation

• AEMO promotes CO oxidation over Au/TiO2 as the electron promoter.
• The promoted effect of AEMO: BaO > SrO > CaO > MgO.
• AEMO endows the more surface electrons of Au sites for CO activation.
• DFT calculation result shows AEMO heighten the Fermi level of TiO2.
• The higher Fermi level of TiO2–AEMO, the higher activity of Au/TiO2–AEMO.

Introduction of alkaline earth metal oxide (AEMO) into TiO2 was found to promote CO oxidation (in the order BaO > SrO > CaO > MgO) over Au nanoparticles supported on TiO2. From experimental (electron-transfer reaction, CO electrochemical oxidation, CO adsorption and Mott–Schottky plots) and theoretical (density functional theory) calculations, it is proposed that AEMO may act as an electron promoter for CO oxidation, but not as an exclusive structural promoter as widely regarded. Introduction of AEMO raises the Fermi level of the TiO2 support, resulting in an enhanced electron transfer from the support to the Au sites and promoting activation of CO adsorbed at Au sites. Moreover, the enhanced catalytic activities induced by AEMO depend on the increase in the Fermi level of the support in the order: TiO2–BaO > TiO2–SrO > TiO2–CaO > TiO2–MgO. This investigation provides a new insight to understand the role of the electron promoters in the thermocatalytic reactions.

The addition of AEMO can raise the Fermi level of TiO2 from EF to EF*. Consequently, the more electrons of TiO2–AEMO will transfer through the Au/supports interface to Au sites, resulting in the promoted activation of CO adsorbed at Au surfaces. Moreover, the electron-donating ability of TiO2–AEMO enhances with the increase of its Fermi level in the following order: TiO2–BaO > TiO2–SrO > TiO2–CaO > TiO2–MgO.Figure optionsDownload as PowerPoint slide