Abstract
Photocatalytic CO2 reduction in water is one of the most attractive research pursuits of our time. In this article we report a giant polyoxometalate {Mo368} based homogeneous catalytic system, which efficiently reduces CO2 to formic acid with a maximum turnover number (TON) of 27,666, turnover frequency (TOF) of 4,611 h−1 and external quantum efficiency of the reaction is 0.6%. The catalytic system oxidizes water and releases electrons, and these electrons are further utilized for the reduction of CO2 to formic acid. A maximum of 8.3 mmol of formic acid was observed with the loading of 0.3 μmol of the catalyst. Our catalyst material is also stable throughout the reaction. The starting materials for this experiment are CO2 and H2O and the end products are HCOOH and O2. The formic acid formed in this reaction is an important H2 gas carrier and thus significant in renewable energy research.
Highlights
The CO2 concentration in environment is ever increasing
Further they have tuned the catalytic activity of Ru(II)-Ru(II) supramolecular photocatalyst [Ru2-Ru(CO)] by employing a suitable reductant to increase formic acid selectivity (87%) and TONHCOOH = 2,766 (Tamaki et al, 2015)
To further prove formic acid is formed in our reaction mixture, a coupling reaction is performed with our reaction solution using the following method
Summary
The CO2 concentration in environment is ever increasing. to find out a suitable pathway to recycle CO2 to an energy rich material is a crucial challenge nowadays (Hoffert et al, 2002; Crabtree and Lewis, 2007; Meinshausen et al, 2009; Mikkelsen et al, 2010; Garai et al, 2012; Bandeira et al, 2015; Twidell and Weir, 2015). The process happens in nature such that first water gets oxidized and releases electrons which further reduce CO2 to carbohydrate in a long catalytic cycle (Hatch, 1976) Drawing inspiration from this process, use of a proper catalytic system can lead to the conversion of CO2 to different high energy carbon material under light. By employing Ru based supramolecular photocatalysts which acts as both light sensitizer and catalyst, Ishitani et al have showed selective reduction of CO2 to formic acid in the presence of an external reductant (Tamaki et al, 2012). In this work a giant {Mo368} POM based homogenous photocatalyst system is used to achieve higher selectivity and TON toward formic acid production by employing water solvent as the electron donor. The catalyst acts with a maximum turnover number (TON) of 27,666 and turnover frequency (TOF) of 4,611 h−1
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