Catalytically Active and Spectator Ce³⁺ in Ceria‐Supported Metal Catalysts

Abstract

Identification of active species and the rate-determining reaction steps are crucial for optimizing the performance of oxygen-storage materials, which play an important role in catalysts lowering automotive emissions, as electrode materials for fuel cells, and as antioxidants in biomedicine. We demonstrated that active Ce(3+) species in a ceria-supported platinum catalyst during CO oxidation are short-lived and therefore cannot be observed under steady-state conditions. Using time-resolved resonant X-ray emission spectroscopy, we quantitatively correlated the initial rate of Ce(3+) formation under transient conditions to the overall rate of CO oxidation under steady-state conditions and showed that ceria reduction is a kinetically relevant step in CO oxidation, whereas a fraction of Ce(3+) was present as spectators. This approach can be applied to various catalytic processes involving oxygen-storage materials and reducible oxides to distinguish between redox and nonredox catalytic mechanisms.

Direct Evidence for the Participation of Oxygen Vacancies in the Oxidation of Carbon Monoxide over Ceria‐Supported Gold Catalysts by using Operando Raman Spectroscopy

“…[20,21] In the case of ceria-supported platinum catalysts, active Ce 3 + speciesw ere detected during reactionb yu sing resonantX -ray emission spectroscopy. [20] Doping ceria with praseodymium increasest he concentration of oxygen vacancies, which in turn was shown to enhance the reactivity. [21] Summarizing, by using operando Ramans pectroscopy we providedd irect spectroscopic evidencef or the participation of oxygen vacancies in CO oxidation over ceria-supported gold catalysts at room temperature.…”

Highly stable and Active Cu1/CeO2 Single‐Atom Catalyst for CO Oxidation: A DFT Study

“…The resulting Ce 3+ ion can activate the corresponding lattice O atom for CO oxidation due to the elongated Ce−O bond length from 2.36 to 2.53 Å. The lower energy cost for CO 2 desorption by Cu 1 /CeO 2 than Pd 1 /CeO 2 also support that the Ce 3+ ‐activated lattice O can facilitate the CO oxidation at the interface of metal‐ceria …”

“…[55] The ion-electron interactions were represented by the projector-augmented wave (PAW) method [56] and the electron exchange-correlation by the generalized gradient approximation (GGA) with the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional. [57] The Kohn-Sham valence states were expanded in a plane-wave basis set with a cut-off energy of 400 eV. The Ce(5 s,5p,6 s,4 f,5d), O(2 s,2p), Cu(3d4 s) and C(2 s,2p) electrons were treated as valence states.…”

Fluorescence-detected XAS with sub-second time resolution reveals new details about the redox activity of Pt/CeO2 catalyst

“…34 mg of 1.5 wt% Pt/CeO 2 catalyst powder (Kopelent et al, 2015) sieved to 100-150 mm grain size was placed into an in situ plug-flow reactor cell (Chiarello et al, 2014) (Fig. 2) between two quartz wool plugs. High-surface-area ceria (85 m 2 g À1 ) in the shape of truncated octahedral particles was prepared by a hydrothermal method.…”

“…This type of research requires the development of highly sensitive spectroscopic methods (Weckhuysen, 2003;Meunier, 2010;Urakawa, 2016;Beale et al, 2010) combined with advanced theory (Campbell, 2017). Spectroscopic methods with sub-second time resolution are needed to detect relevant intermediates (Gott & Oyama, 2009;Burch et al, 2011;Kopelent et al, 2015). Some important catalytic materials also operate under transient conditions.…”