Heterogeneous catalysts for catalytic CO2 conversion into value-added chemicals

As climate change becomes increasingly evident, reducing greenhouse gases including CO₂ has received growing attention. Because CO₂ is thermodynamically very stable, its conversion into value-added chemicals such as CO, CH₄, or C₂H₄ is difficult, and developing efficient catalysts for CO₂ conversion is important work. CO₂ can be converted using the gas-phase reaction, liquid-phase reaction, photocatalytic reaction, or electrochemical reaction. The gas-phase reaction includes the dry reforming of methane using CO₂ and CH₄, or CO₂ hydrogenation using CO₂ and H₂. The liquid-phase reaction includes formic acid formation from pressurized CO₂ and H₂ in aqueous solution. The photocatalytic reaction is commonly known as artificial photo-synthesis, and produces chemicals from CO₂ and H₂O under light irradiation. The electrochemical reaction can produce chemicals from CO₂ and H₂O using electricity. In this review, the heterogeneous catalysts used for the gas-phase reaction or electrochemical reactions are discussed, because the liquid-phase reaction and photocatalytic reaction typically suffer from low productivity and poor durability. Because the gas-phase reaction requires a high reaction temperature of >?600?°C, obtaining good durability is important. The strategies for designing catalysts with good activity and durability will be introduced. Various materials have been tested for electrochemical conversion, and it has been shown that specific metals can produce specific products, such as Au or Ag for CO, Sn or Bi for formate, Cu for C₂H₄. Other unconventional catalysts for electrochemical CO₂ reduction are also introduced.