INFLUENCE OF THE OXIDE SUPPORTS ON AMMONIA-SYNTHESIS ACTIVITY OF UNPROMOTED RUTHENIUM CATALYSTS

Supported ruthenium (Ru) catalysts with Ru loading of 3.5% by weight h ave been prepared by the incipient impregnation method using MgO, gamm a-Al2O3 and ZrO2 as supports. After complete reduction, irreversible h ydrogen chemisorption has been measured on these catalysts at 25-degre es-C and at atmospheric pressure. Ammonia synthesis activities of thes e catalysts have been evaluated in a microflow reactor at 400-degrees- C under atmospheric pressure. It is found that Ru dispersion and metal area change in the order Ru/gamma-Al2O3 > Ru/ZrO2 > Ru/MgO. The ammon ia synthesis activity per gram of the catalyst and the turnover freque ncy change in the decreasing order: Ru/MgO > Ru/gamma-Al2O3 greater-th an-or-equal-to Ru/ZrO2. The activity of Ru/MgO is found to be five-tim es higher than the activities of the other two catalysts. The rate of ammonia synthesis is observed to increase with time on Ru/MgO while it remains it steady on Ru/gamma-Al2O3 d Ru/ZrO2 catalysts. The exceptio nal behaviour of Ru/MgO is explained in terms of pronounced electron d onation by MgO to ruthenium and in terms of possible changes in the cr ystallographic planes of ruthenium under the influence of nitrogen and ammonia under synthesis conditions.