Support effects on the catalytic activity and selectivity of ruthenium in CO and N2 activation

Abstract

CO and N₂ isotopic equilibration reactions have been studied on ruthenium catalysts supported on Al₂O₃, SiO₂ and MgO. The reactivity in CO equilibration was found to follow the sequence: Al₂O₃ > MgO > SiO₂. However, the reactivity on Ru/MgO catalysts was found to be strongly dependent on the activation procedure: samples heated in vacuo at 673 K and then reduced at the same temperature showed the highest activity. The activation does not influence the reactivity of Ru/MgO catalysts towards N₂ isotopic equilibration, where samples directly reduced in H₂ were found to be slightly more active.

The reactivity scale in NH₃ synthesis is as follows: MgO SiO₂ > Al₂O₃, with an apparent activation energy of ca. 100 kJ mol^–1 for all the supports.

The Fischer–Tropsch reaction carried out on samples supported on Al₂O₃ or MgO at ca. 50 atm and 530 K gave rise to a noticeable amount of oxygenated compounds such as alcohols.

Results obtained on the various supports are discussed in terms of the presence of interactions between the metal species and the support itself, which were found to influence the activity and selectivity of the investigated reactions.