Desorption studies of hydrogen and carbon monoxide from nickel surfaces using thermal desorption spectroscopy

The adsorption of hydrogen and carbon monoxide at room temperature on nickel samples was studied with thermal desorption spectroscopy. Desorption from nickel foil was studied using a mass spectrometric method in an ultrahigh vacuum system, while desorption from nickel powder was studied with a microreactor system using a thermal conductivity detector. Two hydrogen desorption peaks are observed at low heating rates (less than 3 K/s). These peaks correspond to the β1 and β2 states observed in single crystals studies. An activation energy of 7–10 kcal/mol is obtained for the low temperature peak (β1 state), assuming first order kinetics, while an energy of 28–30 kcal/mol is obtained for the higher temperature peak (β2 state) with second order kinetics. Desorption spectra using the two different experimental methods are very similar, and the kinetic data derived from the spectra agree well.When the heating rate is high (larger than 12 K/s) only one hydrogen desorption peak is observed, indicating that experim...