Infra-red spectra of carbon monoxide chemisorbed on reduced and oxidized platinum-Aerosil surfaces

The spectra of carbon monoxide chemisorbed on reduced and oxidized platinum-Aerosil-supported pellets have been recorded. The Si—O bands at 1650 and 1850 cm–1 are enhanced by the physical adsorption of a variety of gases on Pt-Aerosil pellets; this enhancement is attributed to an inductive effect. When hydrogen is added to a pellet on which CO has been chemisorbed, bands attributed to the Pt-H stretching frequency that are enhanced by the increased polarity of the bond, are observed. The characteristic of the absorption bands observed for CO chemisorption on reduced Pt-Aerosil pellets confirm previous results. However, when the platinum is oxidized at 300°C by gas-phase oxygen, new bands at 2120 and 2170 cm–1 are developed on subsequent addition of carbon monoxide. These bands are assigned to the stretching frequency of CO chemisorbed on Pt ion and on oxide-ion sites respectively, and the apparent extinction of the former has been measured. After “oxidation”, the oxygen surface species are ineffective in oxidizing CO under conditions where the reaction of chemisorbed oxygen adatoms with CO is rapid.