The promoter effect of lanthana on MgO supported ruthenium catalysts for ammonia synthesis

When activated at high temperature (873 K) doped lanthana such as La2O3, Ce2O3, Sm2O3 derived from nitrate showed remarkable effect on the MgO-supported ruthenium activity for ammonia synthesis. The activity treated with hydrogen at 873 K became 5 times as active as that treated at 623 K. The activity levels were almost the same as those of the Ru-lanthana (support) system under the same activation condition. It was thought that the lanthana was partly reduced and a strong metal support interaction occurred. The partially reduced lanthana was thought to donate electrons to the contacting Ru atoms forming the active centers. The other characters such as the stability were also discussed by comparing with alkali promoters.