The influence of trace oxygen on the catalytic activity of alumina supported Ru in the liquid phase hydrogenation of aromatic
hydrocarbons was studied. The catalytic activity of Ru increased remarkably and the reproducibility was improved by removing
dissolved oxygen from the reactant mixture and carefully refining the catalyst transfer procedure into the reactor to avoid
exposure to air. Trace oxygen affected Ru very severely, but did not affect Rh, Pd, and Pt much. The activity of Ru was lower
than those of Rh, Pd, and Pt in the presence of oxygen as reported in the literature; however, it was the highest when oxygen
was removed carefully. Measurements of the adsorbed oxygen suggested that the activity seriously decreased when only the part
of Ru surface was covered by oxygen. Bimetallic Pt–Ru catalysts demonstrated high activity even in the presence of oxygen.