Isotopic Characterization of NO Adsorption, Dissociation and Coadsorption with CO on Pt(100): an Infrared Reflection-Absorption Study

Abstract

We present the results of the in situ infrared study of the behavior of NO with CO on Pt(100) carried out in a continuous flow reactor at 470 K and 500 K. The frequency of the solitary IR band observed at 470 K during adsorption of nitric oxide shifted by 68-73 cm -1 when we used 15 N 18 O instead of NO. This shift corresponds closely to the square root of the ratio of reduced masses, [μ(NO)/μ 15 N 18 O)] 1/2 , indicating that NO is molecularly adsorbed on the platinum surface even at temperatures as high as 470 K. We did not observe any molecular adsorption of NO at 500 K, though. However, we observed the appearance of an infrared band at ∼1630 cm -1 during the reaction of CO and NO both at 470 K and 500 K. The peak absorbance of this band appears to correlate with high rates of CO 2 production. On the other hand, at low reaction rates, this band completely disappears and is replaced by infrared bands that correspond to a growth of CO adlayer. Isotopic studies utilizing C 18 O showed that the ∼1630 cm -1 wavenumber band is due to molecularly adsorbed NO, indicating that nitric oxide exists largely in undissociated state during its interaction with CO on Pt(100) at elevated temperatures.