Oxidation and reduction of the metal surface in supported Pt using dissociative N₂O adsorption coupled with H₂ and CO titration

Abstract

Not only was the surface site density in a 0.78% Pt/SiO₂ catalyst determined by using selective chemisorption techniques, but the surface chemistry related to decompositive N₂O adsorption on the Pt surface was also described byin situ DRIFTS techniques. The“O”, coverage established by N₂O decomposition at 363 K on a clean Pt surface was equal to thatvia hydrogen adsorption at 300 K; however, both the coverage of chemisorbed oxygenvia O₂ chemisorption at 300 K and the CO_irr coverage were somewhat lower than the“O” monolayer coverage. Surface titration of the“O”-covered Pt crystallites after N₂O decomposition at 363 K gave a consistent Pt_s density with the hydrogen chemisorption.In situ DRIFTS spectra of CO adsorbed at 300 K on both clean and H-covered Pt surfaces exhibited a strong peak at 2,076 cm⁻¹ for linearly adsorbed CO with a small extent of multi-coordinated CO near 1,803 cm⁻¹. The adsorption of CO at 300 K on an“O”,-covered Pt surfacevia dissociative N₂O adsorption at 363 K appeared subsequently a band at 2,186 cm⁻¹ due to a tiny amount of Pt_sO crystallites, which could be completely reduced to H-covered ones, when titrated with H₂ at 300 K. The adequate description for these CO adsorption behaviors on different surfaces is Pt_sO+2CO_(g)→Pt_sCO+CO_2(g), although to very small extent, the addition onto Pt_sO occurs. Spectra of CO adsorbed on the oxidized Pt_s via N₂O decomposition gave consistent surface chemistry within situ gravimetric measurements. The surface reactions acquired by DRIFTS spectra potentially offer an approach to remove N₂O from emission sources by combining its catalytic dissociation with titration of the chemisorbed“O” atoms using either H₂ or CO, particularly H₂ because of complete recovery to a clean Pt_s.