Surface configuration modulation for FeOx-CeO2/γ-Al2O3 catalysts and its influence in CO oxidation

The surface configuration of a catalyst, including the present state, coordination environment and related content of the active and additive species, has dominant effect on its physicochemical properties and catalytic performance. Herein, two types of FeCe/Al catalysts with different surface configurations, FeCe/Al-CI (co-impregnation) and FeCe/Al-SI (stepwise impregnation) were synthesized by adjusting the preparation conditions. Both catalysts together with the reference sample Fe/Al and Ce/Al were characterized by means of XRD, BET, TEM, EPR, UV-vis, Mossbauer spectra, H-2-TPR and XPS. The results showed that (1) in both impregnation modes, ceria presented as small particles, while the iron species existed in two forms: the isolate state (tetrahedral coordination), cluster state (octahedral coordination); (2) iron species in different existence state can be characterized qualitatively or quantitatively via EPR, UV-vis and Mossbauer spectra, and the contents of FeOx clusters follows: FeCe/Al-SI < FeCe/Al-CI < Fe/Al. (3) With the help of HNO3 leaching operation, FeOx clusters were identified as the main active species for CO oxidation. Although Fe/Al sample contained the highest concentration of active cluster FeOx species, the deficiency of Fe-O-Ce structures led to the lowest number of surface oxygen, Ce3+ and Fe2+ species, which resulted in poor CO oxidation activity for Fe/Al catalyst. (C) 2020 Elsevier Inc. All rights reserved.