What are Single Atom Catalysts (SACs)?

Single Atom Catalysts (SACs) can be defined as catalysts made of individual metal atoms uniformly dispersed in a supporting material. These single atoms further serve as active sites for the catalytic reactions; this means that the metal atoms are well utilized and greater catalytic efficiency is achieved. SACs have advantages in activity, selectivity and stability compared to the traditional large atom cluster-based catalysts.

SACs have become a focal point in catalysis research due to their unique properties. Single metal atoms dispersed on the surface of the support like carbon, metal oxides or other materials create a very active site for enhancing the reaction rates and selectivity. This maximization of atom efficiency is needed since many of the catalytic processes require expensive and scarce precious metals. Because one can utilize all those atoms in the catalyst, there will be few losses and the process will be more cost-efficient and less waste, especially for large-scale industries.

Key Applications of SACs

• Environmental Catalysis
  SACs have been found to be highly useful in the removal of pollutants within environmental catalysis because they enhance the degradation of pollutants. They are very active in the removal of volatile organic compounds (VOCs) and the suppression of nitrogen oxides (NOx) within the environment. This makes them very useful in processes aimed at preventing air pollution and promoting green chemistry. SACs have high activity and selectivity, which are useful in the process of degradation of undesirable substances into less hazardous products thereby leading to the production of cleaner air and a healthier environment.
  
  For example, in the case of VOCs oxidation, SACs can achieve high conversion rates compared to other materials at low temperatures, which is critical in energy saving for pollution control. SACs also work selectively, thus they can oxidize specific pollutants without the formation of other toxic species which in turn makes them useful in environmental applications.
  
  
• Energy Conversion
• Fuel Cells: SACs perform with maximum atom efficiency and well-defined active sites. They have been used as part of the electrodes to help facilitate the rate at which reduction/oxidation occurs and the balance between the working electrode and the other electrodes at the reaction surface to improve device efficiency. SACs facilitate enhancement in the efficiency of energy generation or output from the fuel cells and increase their operational lifetime by enhancing the catalytic activity on the electrodes. This is more so when it comes to the advancement of strong and effective fuel cell technology for the enhancement of sustainable energy solutions.
  
  
• Hydrogen Production: SACs are also pivotal in hydrogen production through water splitting. They reduce the energy barriers for the electrolysis of water, making the process more efficient and sustainable. This efficiency is crucial in the identification of cleaner energy technologies as well as phase out fossil fuel dependency and decrease of adverse environmental effects. Due to their high activity and stability under operational conditions, SACs are identified as promising candidates for the large-scale production of hydrogen.
  
  Hydrogen, often considered the fuel of the future, requires efficient production methods to become a viable alternative to fossil fuels. SACs' ability to lower the activation energy for water-splitting reactions means that hydrogen can be produced more efficiently and at a lower cost, which is a significant step toward a sustainable hydrogen economy.
  
• Chemical Synthesis
  In chemical synthesis, SACs are known for their exceptional selectivity and efficiency. They enable precise control over chemical reactions, which is very useful in the formation of organic structures and pharmaceuticals. This makes the industrial processes more efficient as there will be more yields with little by-product formation. Key applications in chemical synthesis include:
  
• Oxidation
  Single Atom Catalysts offer the best characteristics in oxidation reactions since the active site is well-isolated and increases selectivity as well as efficiency. They have found good use in the oxidation of hydrocarbons and alcohols displaying great performance over ordinary catalysts. Due to the high selectivity of SACs in controlling the oxidation states, various reactions that occur minimize the formation of side products.
  
  
• Hydrogenation
  The process of hydrogenation simply put, involves the reaction of hydrogen with an unsaturated compound. SACs, especially those with noble metals such as Pt and Pd, can manifest high efficiency in these reactions. Their single-atom active sites can be controlled and reduced to the lowest levels by not giving rise to multiple side reactions thus enhancing the yield of the final product. This makes SACs of great importance, especially in the manufacture of pharmaceuticals, agrochemicals and fine chemicals.
  
  
• C-C Coupling
  Fundamental in organic synthesis for building complex molecular structures, SACs have proven to be powerful catalysts for C-C coupling reactions, including Suzuki, Heck, and Sonogashira couplings. The single metal active sites in SACs expose the metal atoms independently to react with the substrate. This gives high selectivity in the formation of C-C bonds, thus being widely used in synthesizing pharmaceuticals and fine chemicals. Selectivity in forming carbon-carbon bonds is significant for elaborating complex molecules as fast as possible.
  
  
• Reforming
  Reforming reactions, crucial for producing high-octane fuels and chemicals, benefit significantly from SACs.They improve the effectiveness due to the availability of highly active and stable reaction sites for the catalytic conversion of hydrocarbons. SACs have stable active sites even in harsh conditions due to the strong interactions between the single metal atoms and the support material; this results in high performance as well as durability. This is important for the evolution of better solutions in fuel production to cater to the commercial needs of evolving industries.