The adsorption of CO on hydrated 5 wt % Ru/Al 2 O 3 produced ν CO absorbance features at ∼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 ν CO absorbance feature depends upon the amount of coadsorbed water and (2) the presence of flowing liquid water further red-shifts the frequencies. These ν CO absorbance features are uncorrelated, since the relative intensities of the ν 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 CO 2 desorption peaks. These CO 2 peaks (T ≈ 350, 400, and 550 °C) are most likely the result of the oxidation of adsorbed CO reacting with surface adsorbed water (CO ads + H 2 O ads f H 2 + CO 2 ) and/or the disproportionation of CO (2CO f C ads + CO 2 ). These high-temperature CO 2 desorption peaks suggest that CO strongly adsorbs to hydrated 5 wt % Ru/Al 2 O 3 catalysts. This is corroborated by the fact that intensities of the ν CO absorbance features do not decrease in the presence of flowing liquid water.

The adsorption of CO on hydrated H2-, O2-, H2S-, and He-pretreated 5 wt % Ru/Al2O3 was investigated using attenuated total reflection IR spectroscopy (ATR-FTIR) to determine how the oxidation state of Ru influences CO-H2O interactions. The frequencies of the three IR bands (high frequency (HF), midfrequency (MF), and low frequency (LF)) that are observed when CO adsorbs on Ru/Al2O3 are influenced by (1) CO coverage (CO−CO interactions), (2) Ru oxidation state, (3) pretreatment gas, and (4) pretreatment time. Water red-shifts the CO features by as much as 116 cm−1and influences the MF/LF ratio in a complex mechanism involving both (1) blockage of CO adsorption on the LF site and (2) the formation of OH---CO interactions. While the LF band position is correlated to the adsorbate electronegativity and the MF band slightly correlates to CO coverage, the HF position is independent of either CO coverage or adsorbate electronegativity. These varying degrees of correlations can be rationalized using the extent of interaction between water and the adsorbed CO species by assuming the LF band is due to CO adsorption on an a-top site that is expected to have minimal interaction with coadsorbed water, while the MF and HF bands most likely arise from Ru(CO) m (OH) n (n, m ≥ 1) and Ru(CO) o (H2O) p (o, p ≥ 1), respectively.