The hafnium catalyst refers to a hafnium compound with catalytic properties, typically exhibiting a +4 valence state. Common hafnium compounds include hafnium oxide (HfO2), hafnium tetrachloride (HfCl4), and hafnium hydroxide (H4HfO4), all of which are frequently used as hafnium catalysts. Additionally, hafnium can form complexes with various ligands, which also function as catalysts and can be utilized similarly to ruthenium catalysts. Hafnium catalysts exhibit greater variety compared to other transition metal catalysts. They exhibit a distinct and effective catalytic performance in certain reactions, making them widely employed in organic synthesis.