Stabilizing High Metal Loadings of Thermally Stable Platinum Single Atoms on an Industrial Catalyst Support

Abstract

Single-atom catalysts have attracted attention because of improved atom efficiency, higher reactivity, and better selectivity. A major challenge is to achieve high surface concentrations while preventing these atoms from agglomeration at elevated temperatures. Here we investigate the formation of Pt single atoms on an industrial catalyst support. Using a combination of surface sensitive techniques such as XPS and LEIS, X-ray absorption spectroscopy, electron microscopy, as well as density functional theory, we demonstrate that cerium oxide can support Pt single atoms at high metal loading (3 wt % Pt), without forming any clusters or 3D aggregates when heated in air at 800 °C. The mechanism of trapping involves a reaction of the mobile PtO2 with under-coordinated cerium cations present at CeO2(111) step edges, allowing Pt to achieve a stable square planar configuration. The strong interaction of mobile single-atom species with the support, present during catalyst sintering and regeneration, helps explain the sinter resistance of ceria-supported metal catalysts.

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

“…We note that despite the elevated temperature under oxidizing conditions, Kunwar et.al. demonstrated that Pt is trapped as single atoms on the HSA ceria and that up to 3 wt % Pt can be loaded in the form of single atoms . Before the characterization and kinetic measurements, the catalyst was first oxidized in 20 kPa O 2 (99.999 % Airgas) balanced with He (99.999 % Airgas, equipped with moisture/O 2 trap, Agilent OT3‐2) at 400 °C for 30 min, then flushed with He for 10 min and cooled down to room temperature.…”

“…demonstrated that Pt is trapped as single atoms on the HSA ceria and that up to 3 wt % Pt can be loaded in the form of single atoms. [11] Before the characterization and kinetic measurements, the catalyst was first oxidized in 20 kPa O 2 (99.999 % Airgas) balanced with He (99.999 % Airgas, equipped with moisture/O 2 trap, Agilent OT3-2) at 400°C for 30 min, then flushed with He for 10 min and cooled down to room temperature. To transform the Pt single atoms present in the as synthesized catalyst [6b,11] into Pt nanoparticles, the catalyst was reduced at 300°C for 40 min in 2.5 kPa CO (5 %CO, balance N 2 , certified grade Airgas) balanced with He at 30 sccm total flowrate.…”

“…[6b,8a,b,12] The strong binding of Pt atoms to CeO 2 (111) step edges could be a reason for the low activity. [11] Ganzler et al reported that small Pt clusters supported on CeO 2 are much more active than atomically dispersed Pt and a size of~1.4 nm was reported to be optimal. [10a,13] The origin of the high CO oxidation activity on ceria supported Pt nanoparticles was proposed to be due to highly active sites at the PtÀ CeO 2 interface.…”

Cerium(III) Nitrate Derived CeO2 Support Stabilising PtOx Active Species for Room Temperature CO Oxidation

“…[59][60][61] The intensity of the first peak after absorption edge, so-named as White Line (WL), represents the vacancy in the 5d orbitals of the 5d-metal atoms and can be used for the estimation of its oxidation state. Using the XANES spectra of reference Pt 4 + compounds (individual nitrato complexes) and data from the literature for Pt(acac) 2 (Pt 2 + ), [9,62,63] it can be concluded that the oxidation state of Pt is close to Pt 2 + for the "PtO x /CeO 2 -220" catalyst after activation and at the different temperatures during the catalytic reaction. For the as-prepared catalyst the oxidation state of Pt is less than 4 + but higher than 2 + , this is in a good agreement with the XPS data ( Figure 9, Table 2).…”

“…[1,2] Particularly, catalysts containing platinum deposited on ceria were found to provide an excellent CO conversion at moderate temperatures, keeping their activity after hightemperature stresses. [3][4][5][6][7][8][9][10] The PtÀ Ceria interaction lowers the reaction ignition temperature, which is crucial for preventing air pollution when an engine starts or for autonomous air cleaning systems.…”