Attenuated Total Reflection Fourier Transform Infrared Spectroscopic Investigation of CO Adsorption on Hydrated Ru/Al₂O₃

Abstract

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.

Light at the interface: the potential of attenuated total reflection infrared spectroscopy for understanding heterogeneous catalysis in water

“…46 Further, also on Ru/Al 2 O 3 a red shift was reported for adsorbed CO after co-adsorption of water. 47 The lower L/B ratio with lower wave number shows resemblance with gas phase CO adsorption studies reporting on the effect of increasing support alkalinity on the CO peak position in noble metal catalysts. With increasing support alkalinity the CO bands shifted to lower frequency and the L/B ratio significantly decreased.…”

DRIFTS-QMS Study of Room Temperature CO Oxidation on Au/SiO2 Catalyst: Nature and Role of Different Au Species

“…57 The lone electron pair on the water molecule can be donated to the π orbital of Au. On the one hand, this electron donation effect keeps Au electron rich and from being oxidized.…”

In situ FTIR study on the formation and adsorption of CO on alumina-supported noble metal catalysts from H2 and CO2 in the presence of water vapor at high pressures

“…Using ATR-FTIR, a similar red-shift was also reported by Layman et al for a hydrated Ru/Al 2 O 3 catalyst, which was explained by dipole-dipole interaction between co-adsorbed CO and water molecules. 19 In contrast, Solymosi and Rasko did not observe such a significant shift for a Ru/Al 2 O 3 catalyst that was exposed to CO (ca. 67 Pa) in the presence of water (ca.…”

“…7 shows a broad absorption band at 1800-2040 cm À1 , which may be assigned to linearly adsorbed CO species at about 2020 cm À1 and bridge CO species at 1940 cm À1 . [41][42][43][44][45][46] This broad band increases with CO 2 pressure for the UT-and HT-Ru/ Al 2 O 3 catalysts. Some CO species remained adsorbed on Ru even when the CO 2 pressure was decreased.…”

“…9B indicates a symmetrical shape of the CO adsorption band in the presence of H 2 O, compared to the band leaning to higher frequency in the absence of H 2 O. For this HT sample, an additional absorption band appeared at 1820-1730 cm À1 , which could be assigned to bridge CO. [41][42][43][44][45][46] The adsorption of water may occur on both the Al 2 O 3 support and the noble metals. Unfortunately it was difficult to distinguish the water molecules adsorbed on the support and those on the metals by FTIR measurements.…”