ABSTRACT
The more darkly-shaded elements are those generally used in synthetic reactions. The elements that are lightly shaded are less frequently utilized while the unshaded metals are either infrequently applied or promote only a specific reaction. The extensive use to which nickel has been put as a hydrogenation catalyst makes this metal one of the most common of all such catalysts. As a supported catalyst it is usually associated with processes such as the partial saturation of fats and oils and the hydrogenation of aromatic ring systems. Substances that are deliberately or inadvertently added to a metal catalyst may have an influence on the activity of the catalyst and the selectivity of the reaction. Catalyst modification is brought about because the adsorbed species is either physically blocking the active sites on the metal surface or it is inducing a change in the electronic character or geometric structure of the catalyst surface.
