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The hydrogenation of 1-butene and 1,3-butadiene has been carried out over a series of supported nickel catalysts at 80 °C and atmospheric pressure. It was found that not only the activity but also the selectivity of nickel crystallites could be dramatically altered when the metal was dispersed on graphite nanofibers compared to the performance obtained with more conventional support materials, such as active carbon and γ-alumina. Transmission electron microscopy examinations showed that the metal was evenly distributed over the graphite nanofiber surfaces, and in general the particles adopted a well-defined thin flat hexagonal shape. In contrast, the crystallites formed on active carbon and γ-alumina did not acquire the same well-defined morphological features; however, on average, they were considerably smaller than those generated on the nanofiber surfaces. The most dramatic feature was the fact that in the oxide supported nickel system the average particle size was about 5 times smaller than that for the same metal loading on the graphite nanofibers. Consideration of the particle size distributions in conjunction with the catalyst reactivity data indicates that hydrogenation of either 1-butene or 1,3-butadiene is not directly related to metal dispersion. It is suggested, instead, that differences in the behavioral patterns of the catalyst systems are related to the observed modifications in metal particle morphological characteristics induced by the chemical and structural properties of the support materials. In this context, consideration must also be given to the possibility that the support can induce electronic perturbations in the metallic component, and this feature could be most prominent with a conductive material such as graphite nanofibers.
Chambers et al. (Fri,) studied this question.