Substances containing ytterbium that function as a catalyst is known as ytterbium catalysts. In most ytterbium catalysts, ytterbium has a valence of +3. These catalysts exhibit excellent catalytic properties, making them widely applicable in organic catalysis and environmental protection. For instance, ytterbium(III) chloride (YbCl3) acts as a Lewis acid and can be used as a catalyst in Aldol and Diels–Alder reactions. Additionally, ytterbium(II) iodide (YbI2) can serve as a reducing agent for coupling reactions, similar to samarium(II) iodide.