Pt/CeO2 and Pt/CeSnOx Catalysts for Low-Temperature CO Oxidation Prepared by Plasma-Arc Technique

Abstract

We applied a method of plasma arc synthesis to study effects of modification of the fluorite phase of ceria by tin ions. By sputtering active components (Pt, Ce, Sn) together with carbon from a graphite electrode in a helium ambient we prepared samples of complex highly defective composite PtCeC and PtCeSnC oxide particles stabilized in a matrix of carbon. Subsequent high-temperature annealing of the samples in oxygen removes the carbon matrix and causes the formation of active catalysts Pt/CeOx and Pt/CeSnOx for CO oxidation. In the presence of Sn, X-Ray Diffraction (XRD) and High-Resolution Transmission Electron Microscopy (HRTEM) show formation of a mixed phase CeSnOx and stabilization of more dispersed species with a fluorite-type structure. These factors are essential for the observed high activity and thermic stability of the catalyst modified by Sn. X-Ray Photoelectron Spectroscopy (XPS) reveals the presence of both Pt2+ and Pt4+ ions in the catalyst Pt/CeOx, whereas only the state Pt2+ of platinum could be detected in the Sn-modified catalyst Pt/CeSnOx. Insertion of Sn ions into the Pt/CeOx lattice destabilizes/reduces Pt4+ cations in the Pt/CeSnOx catalyst and induces formation of strikingly high concentration (up to 50% at.) of lattice Ce3+ ions. Our DFT calculations corroborate destabilization of Pt4+ ions by incorporation of cationic Sn in Pt/CeOx. The presented results show that modification of the fluorite lattice of ceria by tin induces substantial amount of mobile reactive oxygen partly due to affecting geometric parameters of ceria by tin ions.

Lattice oxygen activation in transition metal doped ceria

“…In Au-dop-II-VO1, the magnetic moment of the other lattice O atoms are zero, while the magnetic moment of one of the Ce atoms is 0.99 μB, consistent with the formation of one Ce 3+ . In Pt-dop-I, there are no excess electrons, implying that Pt remains formally in the +4 oxidation state, in agreement with experimental data [44][45][46]. On the other hand, for a Pd-CeO2 solid solution, the dominant oxidation state is Pd 2+ [58].…”

“…On the other hand, the barrier is significantly higher for Pt at 1.14 eV. This can well explain the experimentally observed preference for Pt 4+ substitutions in Pt-ceria solid solutions [44][45][46]. The Pt oxidation states in Pt-dop-I and Pt-dop-II are 4+ and 2+, respectively.…”

Programmable Exposure of Pt Active Facets for Efficient Oxygen Reduction

“…In the XPS Pt 4f spectra, the oxidized Pt 2+ state (72.4 eV and 75.7 eV) are inconspicuously observed in the Pt 6.0 % Ni and Pt 3.5 % Ni PFs, whereas substantial Pt 2+ state exists in the Pt 3.0 % Ni PF . Moreover, Pt 4+ (74.6 eV and 77.9 eV) is barely visible in the Pt 3.0 % Ni PF (Supporting Information, Figure S6 c) . It is reasonable that the metallic Pt can be oxidized to Pt 2+ and even Pt 4+ at sufficiently high anodic voltages.…”

A Facile Way for Acquisition of a Nanoporous Pt–C Catalyst for Oxygen Reduction Reaction

“…The data confirm the TEM observations that the coating consists of two crystalline phases, that are: the face‐centered cubic (fcc) Pt (space group Fm −3 m ) and the cubic fluorite CeO 2 (space group Fm −3 m ) structures. [ 41,42 ] The main diffraction peaks at 2θ = 28.6, 33.1, and 40.1, 46.1 correspond to (111) and (200) lattice planes of CeO 2 and Pt, respectively. [ 43 ] The crystallite size of Pt and CeO 2 is calculated to be 4.78 ± 0.16 nm and 2.71 ± 0.1 nm.…”