Coadsorption of carbon monoxide and hydrogen on polycrystalline rhodium

The coadsorption of carbon monoxide and hydrogen on polycrystalline rhodium filament has been studied by thermal desorption mass spectrometry. From a series of thermal desorption spectra of CO and H₂ from rhodium as a function of the exposure time to the gas mixture of CO and H₂, it is indicated that there are a single broad peak for CO and three peaks designated as β₁, β₂, β₃ for hydrogen. Thermal desorption of hydrogen is complex. CO and β₁-hydrogen coadsorb on the rhodium surface with their partial pressures in the initial stage of the exposure to the gas mixture and then the β₁ -hydrogen adsorbed on the surface is replaced by CO with the further exposure time. The kinetics for the replacement of β₁-hydrogen by CO may be discussed from the standpoint of the L-H reaction process. The β₂-and β₃-hydrogen are observed with a longer exposure time after the elimination of β₁ -hydrogen. It may be suggested that the β₃-hydrogen peak is attributed to the desorption of hydrogen absorbed in the bulk. The nature of β₂ -hydrogen is also briefly mentioned in possible implications.