Infrared studies of CO adsorbed on supported PtCo catalysts

Abstract

The IR spectra of CO adsorbed on aerosil-supported Pt, Co, and several PtCo bimetallics have been investigated. It is observed that the addition of Co to Pt causes a decrease in the IR band wavenumber from 2075 to 2040 cu −1 at a given coverage φ(CO). A decrease in the coverage φ(CO) of the Pt and PtCo bimetallic surfaces also gives rise to a red shift, down to 2040 cm −1. For this reason the effect of Co can be regarded as a geometric effect (dilution of the CO layer). The addition of Co to Pt results in the appearance of a second absorption maximum (above 2000 cm −1. at 2086-2083 cm −1. This maximum disappears relatively quickly following pretreatment in n-hexane. It is ascribed here to the adsorption of CO on smooth surfaces. The monometallic Co system differs considerably from the other systems in that (a) its surface is not blocked easily by n-hexane and (b) passing CO at elevated temperatures results in the formation of CO-carbonyl species. In the bimetallic catalysts no Co with this behavior (unalloyed Co) could be detected.