Cobalt Catalysts

The cobalt catalyst refers to an elemental cobalt or cobalt compound which has a catalytic function. Cobalt is a silver-white ferromagnetic metal belonging to the fourth cycle, group VIII in the periodic table. Cobalt is a moderately active metal that does not interact with water at ambient temperatures and does not react in moist air. The common valences of cobalt are +2 and +3. When cobalt is heated to above 300℃ in air, it is oxidized to form CoO. Cobalt can form various cobalt salts, and most of the cobalt salts have catalytic properties. In the application process, a simple cobalt catalyst is usually used, and sometimes a supported cobalt catalyst is used as needed.

Figure 1. Inorganic cobalt catalyst

Applications:

Due to their rich and varied forms, low price and good catalytic effect, cobalt catalysts have many applications in the fields of organic synthesis and environmental protection.

• Organic Synthesis: Carbonylation is one of the important reactions in C₁ chemistry, and is an important method for introducing a carbonyl compound such as a carbonyl group, a synthetic acid or a ketone into an organic compound molecule. The carbonyl cobalt is an important catalyst in the carbonylation reaction, and its common forms are Co₂(CO)₈, HCo(CO)₄ and NaCo(CO)₄. Among them, Co₂(CO)₈ is currently the most commonly used carbonylation catalyst in the industry. As a homogeneous catalyst for carbonylation synthesis, carbonyl cobalt has important applications in the synthesis of organic acids, ketones, ketones and vinegars. The carbonyl cobalt catalyst is mainly used to catalyze the hydroformylation reaction of olefins and alkyne, the carbonyl Reppe reaction, the Pauson-Khand reaction, the amine carbonylation reaction, the carbonylation reaction of methanol, the carbonylation reaction of organic halides, the carbonylation coupling reaction of aromatic hydrocarbons, and the epoxide carbonylation reaction. Fischer-Tropsch synthesis has very important applications in the industry. The Fischer-Tropsch synthesis system is complex and contains a variety of reactions. Fischer-Tropsch synthesis is divided into high temperature Fischer-Tropsch synthesis and low temperature Fischer-Tropsch synthesis. The cobalt-based catalyst has the advantages of high catalytic activity, low water-gas shift reaction activity, high selectivity of heavy hydrocarbons and strong regenerability. Industrially, cobalt-based catalysts can be used in low temperature Fischer-Tropsch synthesis. The active phase of the cobalt-based catalyst is elemental cobalt, and the active phase of cobalt-based catalyst prepared is an oxide of cobalt. Therefore, in the catalytic conversion, it is necessary to reduce the cobalt in the oxidized state to the cobalt in the elemental state of the metal, which is a process of reducing the oxide of the catalyst to a simple substance of the metal. The activity of the cobalt-based catalyst is affected by the content of metallic cobalt, and the decisive factor of the content of elemental cobalt is the interaction between the cobalt oxide of the catalyst precursor and the carrier of the catalyst, and the influence of the interaction between them is controlled by the catalytic activity.

Figure 2. Carbonyl cobalt catalyst

• Environmental Protection: Advanced oxidation technology is the processes of using organic oxidants, electricity, light, catalysts, etc. to degrade organic compounds into low-toxic or non-toxic small molecules, or inorganic substances such as CO₂ and H₂O. Advanced oxidation technology can be used for the treatment of industrial wastewater. The cobalt catalyst can catalyze the decomposition of potassium monopersulfate to produce a radical having strong oxidizing property, thereby acting on the macromolecule of the wastewater and degrading it. Therefore, cobalt catalysts are often used as catalysts for advanced oxidation processes. A large amount of carbon dioxide gas is emitted and triggers the "greenhouse effect" globally. And the "greenhouse effect" poses a series of threats to human survival, such as sea level rise, seawater acidification, climate anomalies, disease transmission, and desertification. Therefore, it is important to convert carbon dioxide molecules into low carbon organic molecules such as carbon monoxide, formic acid, methanol and methane to achieve carbon cycling. The reduction and conversion methods of carbon dioxide are mainly electrochemical methods, photochemical methods, thermochemical methods, and biochemical methods. Among these methods, electrochemical reduction of carbon dioxide has the advantages of simple reaction conditions, easy process control, high conversion rate, easy material acquisition, and easy scale-up production. The use of renewable electrical energy to reduce carbon dioxide by electrochemical means has become the most compelling method. The metal cobalt catalyst with flower-like morphology exhibits extremely high catalytic activity and selectivity in the electroreduction of carbon dioxide, so the metal cobalt catalyst is often used as an electrochemical reduction catalyst for carbon dioxide.

References

1. Choojun, Kittisak. (2019). "Effect of cobalt complex precursors on reactivity of cationic cobalt catalysts: Cyclohexane dehydrogenation." Catalysis Communications 125, 108-113.
2. Han, Xiaopeng. (2019), "Generation of Nanoparticle, Atomic-Cluster, and Single-Atom Cobalt Catalysts from Zeolitic Imidazole Frameworks by Spatial Isolation and Their Use in Zinc-Air Batteries." Angewandte Chemie, International Edition 58(16), 5359-5364.
3. Cheng, Qingpeng. (2019), "Tuning interaction between cobalt catalysts and nitrogen dopants in carbon nanospheres to promote Fischer-Tropsch synthesis." Applied Catalysis, B: Environmental 248, 73-83.