Simultaneous Formation of CO and H₂O₂from CO₂and H₂O with a Ag-MnO_x/CaTiO₃ Photocatalyst

Carbon monoxide (CO) is an important feedstock for the chemical industry, and hydrogen peroxide (H₂O₂) is also an important chemical with versatile applications. Here, a photocatalytic system was discovered for the simultaneous production of CO and H₂O₂from CO₂and H₂O with both high activity and selectivity without any externally applied voltage and any consumption of chemical compounds, which was promoted by using a calcium titanate (CaTiO₃) photocatalyst modified with a silver-manganese oxide (Ag-MnO_x) dual cocatalyst. Although a Ag/CaTiO₃(CTO) photocatalyst was reported to reduce CO₂with water to form CO and O₂, the coexistence of MnO_xspecies with silver nanoparticles (NPs) not only improved the CO formation rate more than 2 times with a selectivity of 76% but also changed the selectivity of the oxidative reaction and forms H₂O₂instead of O₂with a high selectivity of 99%. The Ag NPs promoted the CO₂reduction to CO by the photoexcited electrons, and the Mn(III) oxide species deposited on the CaTiO₃surface contributed to the water oxidation to H₂O₂by the positive holes in the aid of HCO₃^-as a reaction mediator. The produced CO is easily separated from the aqueous solution to the gas phase, and the H₂O₂is stably stored in the aqueous HCO₃^-solution. This photocatalytic system can utilize the stable and ubiquitous molecules (CO₂and H₂O) to produce reactive and useful molecules (CO and H₂O₂), concurrently, meaning that it can convert photoenergy to storable chemical energy to increase sustainability.