Sm-promoted alumina supported Ru catalysts for ammonia synthesis: Effect of the preparation method and Sm promoter

► Sm promoted chlorine-free Ru/Al2O3 catalyst was prepared by precipitation method. ► Chlorine suppressed the hydrogen desorption peak in the temperature range of 150 to 325 °C. ► The presence of Sm significantly decreased the amount of adsorbed hydrogen. ► The activity of Sm -Ru/Al2O3 catalysts increased firstly and then decreased with increase in Sm loading.