Adsorption and oxidation of carbon monoxide on Pt/C, Pt3Co/C, and PtRu/C catalysts studied by in-situ attenuated total reflection Fourier-transform infrared.

The adsorption and oxidation of CO on commercial nanoparticle catalysts supported on carbon black (Pt/C, Pt3Co/C, PtRu/C) were examined at 23, 40, and 60 degrees C in 0.1 M HClO4 by use of in situ ATR-FTIR (attenuated total reflection Fourier-transform infrared) spectroscopy. Absorption bands for the adsorbed CO assigned to linear (atop) CO (CO(L)) and bridge CO (CO(B)) were observed around 2040 cm(-1) and 1850 cm(-1), respectively, at high CO coverage theta(CO) close to 0.8 on all three types of catalysts. The adsorption rates of both CO(L) and CO(B) at the initial stage were found to decrease in the order Pt/C > Pt3Co/C > PtRu/C, indicating that the interaction of CO with PtRu is weakest. The adsorption of CO on these catalysts resulted in the growth of a sharp O-H stretching band around 3630 to 3640 cm(-1), which was assigned to non-hydrogen-bonded water molecules (isolated H2O) co-adsorbed with CO. For the electrooxidation reaction of CO, PtRu/C exhibited the highest activity at all temperatures. It was confirmed that the dominant factor for determining CO oxidation activity was the onset potential for the oxidation of isolated H2O, E(onset)(H2O), to provide an oxygen species that is consumed in either a Langmuir-Hinshelwood mechanism (Pt/C, Pt3Co/C) or the bi-functional mechanism (PtRu/C). In addition, PtRu/C exhibited the weakest Pt-CO interaction. The values of E(onset)(H2O) at PtRu/C were lowest among the three catalysts from 23 to 60 degrees C. With increasing temperature, the E(onset)(H2O) at Pt/C and Pt3Co/C shifted to less positive potential, resulting in increased CO oxidation activity, while the shift in E(onset)(H2O) at PtRu/C was relatively small.