Carbon-supported bimetallic catalysts containing iron: II. Catalytic behaviour in benzene hydrogenation and thiophene hydrodesulphurization

Abstract

Carbon-supported bimetallic transition metal catalysts containing iron as common metal, have been prepared by successive impregnations of activated carbon with solutions of metal salts in ethanol, followed by drying and “in situ” reduction. Their behaviour both in benzene hydrogenation (101 kPa, 300–450 K) and thiophene hydrodesulphurization (101 kPa, 673 K) reactions has been tested in a glass microflow reactor. The presence of iron in the bimetallic catalysts originates a decrease in the specific activity for benzene hydrogenation. This effect being more important in noble metal containing catalysts (Fe-Ru, Fe-Pt), than in those containing first-row elements (Fe-Co, Fe-Ni). Furthermore, while specific activities for thiophene hydrodesulphurization are similar to that of the more active component for the Fe-Co and Fe-Ni systems, noble metal containing catalysts (Fe-Ru, Fe-Rh, Fe-Pd, Fe-Pt, Fe-Ir) show lower specific activities than their noble metal monometallic counterparts. A drastic decrease in hydrogenation capability both for the benzene to cyclohexane reaction and for the butenes to butane step in thiophene hydrodesulphurization was also observed when iron is added to the catalysts. Especially for samples containing noble metals, these results can be readily explained on the basis of a model which proposes the presence of a true iron-metal alloy in these catalysts, and by the fact that the catalytic properties of the alloyed phases are different from that of the corresponding single components.