Transition metals are excellent catalysts due to their unique ability to adopt multiple oxidation states and form complexes.

Transition metals are located in the central part of the periodic table, specifically in groups $3$ to $12$. One of their defining characteristics is their capacity to exhibit multiple oxidation states, which means they can lose varying numbers of electrons, resulting in the formation of different types of ions. This property is essential for their catalytic role, as it enables them to facilitate a wide array of chemical reactions by providing an alternative reaction pathway that has a lower activation energy.

In addition to their variable oxidation states, transition metals can also form complexes. A complex consists of a central metal ion surrounded by molecules or ions known as ligands. These ligands can donate electron pairs to the metal ion, establishing coordinate bonds. The ability to form such complexes enhances the catalytic versatility of transition metals, allowing for interactions with a diverse range of reactants.

Moreover, transition metals typically possess partially filled $d$ orbitals. The ability of these orbitals to overlap with the orbitals of other atoms enables the formation of strong bonds. This bonding capability significantly contributes to the efficiency of transition metals as catalysts.

For instance, in the Haber process, iron is employed as a catalyst to convert nitrogen and hydrogen into ammonia. The iron provides a surface for the reactants to adsorb onto, while its variable oxidation states facilitate the breaking and forming of bonds during the reaction. Similarly, in the Ostwald process, platinum serves as a catalyst for the conversion of ammonia into nitric acid. Here, platinum forms a complex with ammonia, reducing the activation energy of the reaction and thereby accelerating the process.

In conclusion, the ability of transition metals to adopt multiple oxidation states, form complexes, and establish strong bonds with other atoms renders them highly effective catalysts. Their versatility allows them to facilitate a broad spectrum of chemical reactions, making them invaluable in numerous industrial processes. To gain further insights into how transition metals leverage their properties in various applications, consider exploring related literature on the subject.