Modifications in the catalytic properties of nickel supported on different dielectric oxides

The hydrogenation of 1-butene and 1,3--butadiene has been carried out over a series of dielectric-oxide-supported nickel catalysts at temperatures ranging from 60 to 120 degreesC and atmospheric pressure. The catalytic activity and selectivity of these systems were found to be extremely sensitive to the nature of the support medium, the hydrogen content of the reactant gas mixture, and the reaction temperature. High-resolution transmission electron microscopy examinations provided evidence that the active state of the catalyst was associated with the partial reduction of the support, particularly in the vicinity of the dispersed metal phase. With some of the dielectric oxides it was essential for the system to remain on stream for prolonged periods of time to achieve the optimum activity. It is proposed that the induction period is related to the time required to reduce the support to a lower oxide state, which is capable of inducing electronic perturbations in the dispersed metal particles. It is suggested that the initial role of the metal in this interaction is to function as a dissociation center for hydrogen, thus providing a source of atomic species for the subsequent partial reduction of the support. It was significant to find that when nickel was supported on gamma-alumina, an oxide that does not undergo this type of transformation, the catalytic performance for the respective hydrogenation reactions under these conditions was extremely poor.