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 Ce_1-xPt_xO_2-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 Ce_1-xPt_xO_2-δ, creating oxide ion vacancies leading to a strong Pt²⁺-CeO₂ interaction that is responsible for higher catalytic activity.