A novel high-pressure photoreactor for CO2 photoconversion to fuels

CO2 is among the most stable molecules, requiring high amounts of energy to be activated. Photosynthesis allows the conversion of CO2 and H2O, the major products of combustion, into useful organic compounds and represents one of the most efficient ways for CO2 capture, besides its absorption in oceanic water. This is a natural but complex process leading to a regenerated fuel by photo-irradiation. The natural process has never been mimicked in laboratory, due to the complexity of the enzymatic reactions involved. In spite of this, the topic is intriguing and it raised interest in the late 70s with the rst attempts to x CO2 at least by partially reducing it to CO. However, the results were not satisfactory for different reasons. The rst was a lack of knowledge on the basics of materials science for photocatalysis at that time, now partly overcome by many reports, although for different applications (e.g. photodegradation of pollutants). Another reason was that the limited solubility of CO2 in water (0.03 M at 25 C, 1 atm CO2), especially at relatively high temperature which could improve the kinetics, always led to very poor productivity. Some attempts with different solvents, e.g.methanol or acetonitrile (solubility 0.2 M and 0.3 M, respectively), allowed to increase solubility, but at the expenses of a less sustainable solution. However, no impressive increase of CO2 conversion was observed. Some researchers tried to develop catalytic solutions based on supramolecular chemistry and homogeneous catalysis through e.g.metalloporphyrins and Re or Ru complexes, which however suffer of many drawbacks: difficult synthesis of the