Effect of Zn Content on Catalytic Activity and Physicochemical Properties of Ni-Based Catalysts for Selective Hydrogenation of Acetylene

Abstract

The influence of zinc addition on the catalytic performance andphysicochemical properties of nickel-based catalysts used inselective hydrogenation of acetylene was investigated. It was foundthat the activity and selectivity to ethylene of the nickel-basedcatalysts were positively modified by incorporation of zinc intotheir solid structure. The zinc-modified catalysts produced smalleramounts of coke and methane than those not containing zinc. Cokedeposition had a strong effect on the ethylene selectivity.However, this influence was much more significant for zinc-modifiedcatalysts than for nonmodified nickel-based solids. These resultswere explained taking into account the different crystallinestructures obtained for both types of solid. In the case ofzinc-modified catalysts, the metal nickel phase was interactingstrongly and highly interdispersed in a nonstoichiometric zincaluminate spinel matrix. The high interdispersion of the metal nickelphase diminished the number of three-nickel-atom arrangementsnecessary for the formation of surface intermediates that led to cokeand methane production. The nonmodified nickel-based solids, however,were composed of large metal crystallites on which coke and methaneprecursors were very easily formed. The high interaction betweenmetal nickel particles and the zinc aluminate matrix preventedwhisker formation to some extent. Finally, the low concentration ofacid sites on the solid surface considerably reduced amorphous-likecoke deposition.