INFRARED SPECTROSCOPIC STUDIES OF CO ADSORPTION BY METALS - EFFECT OF OTHER GASES IN ADSORPTION

The infrared spectra of CO adsorbed by metals supported on silica have been compared with the electronic configuration of the metal phase. Data on the metals Ir, Os, Re, Rh, Ru, and Au plus other published data indicate a correlation between the bond order of adsorbed CO in linear M-CO species and the number of d holes of the metal. Treatment of the metal surfaces with gases affects the position and intensity of the CO bands. The treatment of Rh, Ir, and Os with O2 shifts the M-CO band to higher frequencies and suppresses the band corresponding to two CO molecules per metal site for Ir and Os. The effect of H2S is generally opposite to that of O2, and NH2 has an intermediate effect. H2S on Ir and Os shifts the M-CO band to lower frequencies and on Rh it enhances the band attributed to two CO molecules per metal site but eliminates the bridged Rh2-CO species. The exposure of clean Re to O2, NH3, and H2S blocks completely the adsorption of CO. These gases on Ru decreased only slightly the intensity of the CO bands. Some changes of the spectra of adsorbed CO reflecting catalytic or poisoning activity of other gases toward carbonyl formation may be explained by electronic interactions and steric factors. © 1969.