The Influence of Metal Loading on the Structure-sensitive Chemisorption of Nitrogen on Ru/γ-Al 2 O 3 Catalysts †

Abstract

Nitrogen chemisorption has been studied on five Ru/γ-Al₂O₃ catalysts ranging in Ru loading from 0.5–5.0 wt.% at different temperatures from 25°C to 300°C and at different pressures up to 1 atm in order to obtain an insight into the influence of the morphological structure of ruthenium on the amount and nature of nitrogen chemisorption. The chemisorption of N₂ at ambient temperature increased steadily with pressure on all the catalysts studied so that the resulting isotherms were straight lines. When the adsorption temperature was raised, N₂ chemisorption decreased and the corresponding isotherms developed three adsorption steps. These three adsorption steps are attributed to structure-sensitive nitrogen chemisorption on the three low Miller index planes of ruthenium, i.e. (101), (100) and (001). When the nitrogen uptakes at 740 Torr as taken from the adsorption isotherms were plotted against the Ru loadings, a maximum was obtained at an Ru loading of 2.5 wt.% which corresponds to an Ru crystallite size of 4 nm, suggesting that N₂ chemisorption is a highly structure-sensitive phenomenon on these catalysts.