Attenuated total reflection Fourier transform infrared spectroscopic investigation of CO adsorption on hydrated Ru/Al2O3

The adsorption of CO on hydrated 5 wt % Ru/Al2O3 Produced nu(CO) absorbance features at similar to 2048, 1992, and 1924 cm(-1) that are red-shifted by 50-116 cm(-1) from those seen in the absence of water (2020-2040, 2080, and 2140 cm(-1)). This red-shift most likely arises from dipole-dipole interaction between coadsorbed CO and water molecules since (1) the exact frequency of the nu(CO) absorbance feature depends upon the amount of coadsorbed water and (2) the presence of flowing liquid water further red-shifts the frequencies. These nu(CO) absorbance features are uncorrelated, since the relative intensities of the nu(CO) absorbances at 2049, 1992, and 1924 cm-1 depend on the amount of coadsorbed water and CO on the surface. Temperature programmed desorption done with TGA-MS indicated three different high-temperature CO2 desorption peaks. These CO2 peaks (T approximate to 350, 400, and 550 degrees C) are most likely the result of the oxidation of adsorbed CO reacting with surface adsorbed water (COads + H2Oads -> H-2 + CO2) and/or the disproportionation of CO (2CO -> C-ads + CO2). These high-temperature CO2 desorption peaks suggest that CO strongly adsorbs to hydrated 5 wt % Ru/Al2O3 catalysts. This is corroborated by the fact that intensities of the nu(CO) absorbance features do not decrease in the presence of flowing liquid water.