Visible-light-driven methane formation from CO2 with a molecular iron catalyst

Converting CO2 into fuel or chemical feedstock compounds could in principle reduce fossil fuel consumption and climate-changing CO2 emissions. One strategy aims for electrochemical conversions powered by electricity from renewable sources, but photochemical approaches driven by sunlight are also conceivable. A considerable challenge in both approaches is the development of efficient and selective catalysts, ideally based on cheap and Earth-abundant elements rather than expensive precious metals. Of the molecular photo- and electrocatalysts reported, only a few catalysts are stable and selective for CO2 reduction; moreover, these catalysts produce primarily CO or HCOOH, and catalysts capable of generating even low to moderate yields of highly reduced hydrocarbons remain rare. Here we show that an iron tetraphenylporphyrin complex functionalized with trimethylammonio groups, which is the most efficient and selective molecular electro- catalyst for converting CO2 to CO known, can also catalyse the eight-electron reduction of CO2 to methane upon visible light irradiation at ambient temperature and pressure. We find that the catalytic system, operated in an acetonitrile solution containing a photosensitizer and sacrificial electron donor, operates stably over several days. CO is the main product of the direct CO2 photoreduction reaction, but a two-pot procedure that first reduces CO2 and then reduces CO generates methane with a selectivity of up to 82 per cent and a quantum yield (light-to-product efficiency) of 0.18 per cent. However, we anticipate that the operating principles of our system may aid the development of other molecular catalysts for the production of solar fuels from CO2 under mild conditions.Fil: Rao, Heng. Université Paris Diderot - Paris 7; FranciaFil: Schmidt, Luciana Carina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina. Université Paris Diderot - Paris 7; FranciaFil: Bonin, Julien. Université Paris Diderot - Paris 7; FranciaFil: Robert, Marc. Université Paris Diderot - Paris 7; Franci

Synergistic geometric and electronic effects for electrochemical reduction of carbon dioxide using gold–copper bimetallic nanoparticles

Highly efficient and selective electrochemical reduction of carbon dioxide represents one of the biggest scientific challenges in artificial photosynthesis, where carbon dioxide and water are converted into chemical fuels from solar energy. However, our fundamental understanding of the reaction is still limited and we do not have the capability to design an outstanding catalyst with great activity and selectivity a priori. Here we assemble uniform gold-copper bimetallic nanoparticles with different compositions into ordered monolayers, which serve as a well-defined platform to understand their fundamental catalytic activity in carbon dioxide reduction. We find that two important factors related to intermediate binding, the electronic effect and the geometric effect, dictate the activity of gold-copper bimetallic nanoparticles. These nanoparticle monolayers also show great mass activities, outperforming conventional carbon dioxide reduction catalysts. The insights gained through this study may serve as a foundation for designing better carbon dioxide electrochemical reduction catalysts

Biological Production of Hydrogen

The production of H2 from renewable sources, such as water or biomass, is a sustainable strategy for energy supply. Hydrogenases are the only enzymes that specifically catalyze the reversible reaction of H2 production/uptake with almost no overpotential. In this chapter, we review the advances produced in the last decade in the biocatalytic production of H2, including systems based on isolated hydrogenases as well as those using microorganisms through dark fermentation processes