Lanthanum Catalysts

The lanthanum catalyst refers to an elemental lanthanum or lanthanum compound which has a catalytic function. Lanthanum is a silver-white rare earth metal that is soft and easy to cut and has ductility. Metal lanthanum is chemically active. Lanthanum is easily oxidized in the air, and its fresh surface quickly darkens when exposed to air. Lanthanum burns when heated to form oxides and nitrides. Lanthanum is heated in hydrogen to form a hydride, and when it’s reacting with hot water, hydrogen is evolved. The common valences of lanthanum have 0, +1, +2 and +3. The valence of ruthenium in most lanthanum catalysts is +3, such as lanthanum oxide, lanthanum chloride, and the like. In the earth's crust, lanthanum is present in monazite sand and bastnasite.

Figure 1. Lanthanum catalyst

Applications:

Lanthanide not only enhances the activity of the reaction in organic synthesis, but also improves the selectivity of the reaction and has a special catalytic effect. Metal lanthanum, as one of the lanthanides, also has a good catalytic effect. In particular, some lanthanum compounds (such as lanthanum oxides and lanthanum salts) have a wide range of applications in organic synthesis. In addition, lanthanum catalysts have certain applications in environmental protection.

• Polymerization: Polycaprolactone is a linear aliphatic polyester obtained by ring-opening polymerization of caprolactone. It has unique biodegradability, biocompatibility and good permeability, and is widely used in biomedical technology. The aryloxy rare earth complexes are a class of catalysts that efficiently catalyze the polymerization of caprolactone. La(ODTBP)₃ is an aryloxy rare earth complex which can catalyze the ring-opening polymerization of caprolactone to synthesize polycaprolactone.
• Condensation reaction: Ortho-Phenylphenol (OPP) is a highly versatile fine chemical and organic intermediate. The most widely used polycaprolactone synthesis method is cyclohexanone condensation dehydrogenation. Lanthanum phosphotungstate (LaPW₁₂O₄₀) has good catalytic activity for the condensation dehydrogenation of cyclohexanone, and the yield of the obtained product is high. Industrially, lanthanum phosphotungstate can be used as a catalyst for the condensation dehydrogenation of cyclohexanone, and the cyclohexanone self-condensation reaction is carried out in different water-carrying agents. The Biginelli reaction is one of condensation reactions and can be used to synthesize 3,4-dihydropyrimidin-2-one compounds. LaCl₃·7H₂O was used as a catalyst to catalyze the Biginelli reaction of ethyl acetoacetate, aromatic aldehyde and urea to synthesize 3,4-dihydropyrimidin-2-one derivatives in high yield.

Figure 2. Lanthanum phosphotungstate catalyzed condensation reaction

• Coupling reaction: Rare earth metal oxides have high catalytic activity and selectivity for the coupling reaction and also exhibit good stability at high temperatures. Oxidation coupling of methane (OCM) can be catalyzed by using lanthanum oxide as a catalyst.
• Environmental protection: TiO₂ is often used as a photocatalyst to degrade wastewater containing organic dyes. However, the TiO₂ band gap energy is relatively high, and the photogenerated electron-holes are easily recombined, resulting in poor photocatalytic degradation of organic dye-containing wastewater. By modifying the TiO₂ by adding metal lanthanum, the band gap energy can be reduced, the photogenerated electron-hole recombination can be inhibited, and the photocatalytic activity can be improved. The supported TiO₂ catalyst can be prepared by sol-gel method by loading TiO₂ onto mesoporous molecular sieve SBA-15 and then modifying TiO₂-SBA-15 with lanthanum. The catalyst has a good photocatalytic degradation effect on methyl orange solution and can be used to purify organic dye wastewater.

References

1. Magyar, Agnes. (2017). "Molecular sieve supported lanthanum catalyst for the efficient synthesis of polyhydroquinolines via Hantzsch synthesis." Periodica Polytechnica, Chemical Engineering 61(4), 278-282.
2. Liao, Hongguang. (2018), "Benzene hydrogenation over polydopamine-modified MCM-41 supported Ruthenium-Lanthanum catalyst." Inorganic and Nano-Metal Chemistry 48(12), 599-606.
3. Teng, Huai-Long. (2017), "Diastereodivergent Asymmetric Carboamination/Annulation of Cyclopropenes with Aminoalkenes by Chiral LanthanumCatalysts" Journal of the American Chemical Society 139(46), 16506-16509.