Surface status and reduction behavior of porous ceria (CeO2) via amended EISA method

Abstract

Ceria (CeO2) powder with multi-scale porosity was synthesized by evaporation induced self-assembly (EISA) strategy using tri-block copolymer (P123) as the template. The product was characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM), transmission electronic microscopy (TEM), and N2 adsorption–desorption isotherms. Reducing property and repeatability were tested by temperature programmed H2 reduction (TPR). Oxygen storage capacity (OSC) was calculated according to the Gaussian–Lorentz deconvolving to the TPR curves. The results showed that the product possessed multi-scale porosity, sizes of the pores were in the ranges of ∼40μm, ∼2μm and <0.3μm, respectively. Specific surface area of the porous CeO2 was 32.5m2/g. Mechanism in the reduction of surface, near surface and inner parts of porous CeO2 were discussed. Carbonate groups remained on the surface when CeO2 were calcined below 600°C. The initial H2-TPR yielded an OSC of 383mol O2/g, which was attributed to oxygen release from the surface nanocrystals, (near) surface sites as well as the inner parts. While the repeated tests showed an OSC of 418mol O2/g, which was associated with the diminished reaction before 620°C and the enhanced reduction around 782°C. A schematic was proposed for the preparation of CeO2 with multi-scale porosity in the amended EISA strategy, based on the characterization results, and the strategy may provide a candidate to obtain catalyst with excellent properties.