Promoting Effect of CeO₂ in Combustion Synthesized Pt/CeO₂ Catalyst for CO Oxidation

Abstract

A 1% Pt/CeO2 catalyst prepared by the solution combustion method shows a higher catalytic activity for CO oxidation by O2 compared to Pt metal particles. At least six hydrogen atoms are taken up per Pt at −25 °C. The structure of 1% Pt/CeO2 catalyst has been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. Rietveld refinement shows that Pt ions are incorporated into the CeO2 matrix in the form of Ce1 - x Pt x O2 - δ solid solution. A decrease in oxygen content in 1% Pt/CeO2 is seen in relation to pure CeO2. TEM studies show that Pt is dispersed as atoms or ions and only a small amount as Pt metal particles. The Pt(4f) core level region in XPS shows that Pt is present mostly in the Pt2+ ionic state on CeO2 surface. FTIR of 1% Pt/CeO2 shows a strongly adsorbed CO peak at 2082 cm-1 corresponding to oxidized Pt. These structural studies show that Pt ions in the catalyst are substituted for Ce4+ ions in the form of Ce1 - x Pt x O2 - δ, creating oxide ion vacancies leading to a strong Pt2+−CeO2 interaction that is responsible for higher catalytic activity.

Surface sites on Pt–CeO2mixed oxide catalysts probed by CO adsorption: a synchrotron radiation photoelectron spectroscopy study

“…Pt-CeO 2 mixed oxides that contain ionic Pt species can be prepared by several methods, including solution combustion, 3,4,9,10 r.f. magnetron sputtering, [11][12][13] and co-deposition of Pt and Ce in the oxygen atmosphere.…”

The origin of the enhanced oxygen storage capacity of Ce1−x(Pd/Pt)xO2

“…16 The presence of these lower valence dopant ions results in the formation of charge-compensating oxygen vacancies neighbouring the dopant, which are observed in extended X-ray absorption fine structure (EXAFS) experiments. 9,17,18 For Pd and Pt, doping is formally described as…”

“…The charge-compensating vacancy formation energies in this case 42 Our results indicates that the NM IV to NM II plus charge-compensating vacancy transition is in fact spontaneous, which is consistent with experiment, with a charge-compensating vacancy expected to be neighbouring the dopant. 9,17,18 The failure to account for the large lattice distortion explains why Hermansson and co-workers predicted the incorporation of the noble metal at a higher oxidation state, and the formation of the charge-compensating vacancy to be a reduction. It is also instructive to note that, in supercell defect calculations, breaking of the symmetry has been shown to be vital to obtain quantitatively accurate defect geometries.…”

In situ FT-IR Spectroscopic Studies on the Mechanism of the Catalytic Oxidation of Carbon Monoxide over Supported Cobalt Catalysts

“…There are several reports describing the use of noble metals (Pt, Pd) for CO oxidation [1][2][3][4][5][6][7]. However, the high cost of noble metals and their sensitivity to sulfur poisoning have stimulated the search for substitute catalysts.…”