The surface evolution of a catalyst jointly influenced by thermal spreading and solid-state reaction: A case study with an Fe2O3–MoO3 system

The design and control of the surface is extremely important for the development of heterogeneous catalysts because surface properties always play a key role in catalytic performance. Therefore, it is of great interest to investigate the evolution of the surface state during the preparation of a catalyst. Mixed oxides are a particularly important group of catalytic materials. This work studied Fe2O3–MoO3 as a model system, investigating the surface states jointly influenced by the thermal spreading of MoO3 and the solid-state reaction that produces Fe2(MoO4)3 during heat treatment. X-ray photo-electron spectroscopy, scanning electron microscopy and 57Fe Mössbauer analysis were used to characterize the evolution of the surface and the bulk of solids, and the oxidation of methanol to formaldehyde was also used as a probe reaction. It was found that the evolution of the surface layer takes place mainly as follows: (i) a small amount of MoO3 can be dispersed onto the surface of Fe2O3 via grinding; (ii) the thermal spreading of MoO3 and the solid-state reaction start almost simultaneously at around 400 °C, leading to the coexistence of MoO3 and Fe2(MoO4)3 species on the surface of Fe2O3 grains; (iii) further thermal spreading and the solid-state reaction yield a shell of Fe2(MoO4)3 encapsulating the remaining Fe2O3 grains, but a small amount of MoO3 remains on the external surface of the resulting Fe2(MoO4)3 shell; (iv) when the MoO3 grains run out, the surface MoO3 species also disappears.

Graphical abstractMixed oxides are a particularly important group of catalytic materials, and it is of great interest to investigate the evolution of the surface state during the preparation of a catalyst. This work studied Fe2O3–MoO3 as a model system, investigating the surface states jointly influenced by the thermal spreading of MoO3 and the solid-state reaction that produces Fe2(MoO4)3 during heat treatment.Figure optionsDownload full-size imageDownload as PowerPoint slide