Tuning Pt-CeO2 interactions by high-temperature vapor-phase synthesis for improved reducibility of lattice oxygen

Abstract

In this work, we compare the CO oxidation performance of Pt single atom catalysts (SACs) prepared via two methods: (1) conventional wet chemical synthesis (strong electrostatic adsorption–SEA) with calcination at 350 °C in air; and (2) high temperature vapor phase synthesis (atom trapping–AT) with calcination in air at 800 °C leading to ionic Pt being trapped on the CeO2 in a thermally stable form. As-synthesized, both SACs are inactive for low temperature (<150 °C) CO oxidation. After treatment in CO at 275 °C, both catalysts show enhanced reactivity. Despite similar Pt metal particle size, the AT catalyst is significantly more active, with onset of CO oxidation near room temperature. A combination of near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and CO temperature-programmed reduction (CO-TPR) shows that the high reactivity at low temperatures can be related to the improved reducibility of lattice oxygen on the CeO2 support.

Origin of the High CO Oxidation Activity on CeO2 Supported Pt Nanoparticles: Weaker Binding of CO or Facile Oxygen Transfer from the Support?

“…The XANES and EXAFS results are consistent with the average size and small fraction of single atoms observed from the STEM images. Additionally, the results are in agreement with in‐situ XPS results on the same catalyst after activation in CO, where a small percentage of Pt 2+ was detected …”

“…In addition to the small Pt clusters, a small fraction of Pt is present as isolated Pt atoms. The average particle size of the Pt clusters was 1.5–2 nm (the size was similar before and after reaction, not shown) which is similar to the size previously reported by Pereira‐Hernández et al . after the same activation pretreatment.…”

“…showed that CeO 2 traps Pt as isolated single atoms when the catalyst is oxidized at 800 °C, and the Pt single atoms remain very stable under reaction conditions . However, Pt single atoms prepared by atom trapping and other methods were shown to have very low activity compared to nanoparticles . The strong binding of Pt atoms to CeO 2 (111) step edges could be a reason for the low activity .…”

“…The authors proposed a reaction mechanism where CO on the Pt reacts with oxygen provided by CeO 2 . Evidence for a redox cycle and Ce 3+ being an active species in the reaction was shown by in‐situ x‐ray emission, x‐ray absorption and x‐ray photoelectron spectroscopies. These reports indicate that the reducibility of ceria is important for the catalytic activity during CO oxidation.…”

“…These reports indicate that the reducibility of ceria is important for the catalytic activity during CO oxidation. In fact, Pereira‐Hernández et al . showed that for similar size nanoparticles (∼1.5 nm), the catalyst with more reducible CeO 2 was more active.…”