Adsorption—Desorption of Hydrogen on Tungsten and Molybdenum

Abstract

Adsorption of hydrogen on tungsten and molybdenum was investigated over the range 300° to 1000°K using a mass spectrometer. These phenomena alone are observed below about 1200°K. A mass spectrometer affords a practical method for studying different adsorbates simultaneously adsorbed. Although the method is less sensitive than those depending on measurements of total pressure, it does not require the dangerous assumptions made tacitly in much published work employing the latter method. Molecular hydrogen is readily desorbed below 900°K from both W and Mo, although somewhat less so from Mo. The amount remaining is probably not over 10^—5 monolayer. Over the experimental range, only one mode of adsorption—desorption is detected. Despite intense effort, CO, H₂O, and CH₄ were nevere liminated. CO is much more tenaciously bound than hydrogen and thus may have confused earlier measurements for hydrogen. H₂O and CH₄ do not compete successfully with hydrogen for adsorption sites; they are less tenaciously adsorbed and their abundance was low.