High Pressure Photoreduction of CO₂: Effect of Catalyst Formulation, Hole Scavenger Addition and Operating Conditions

Abstract

The photoreduction of CO2 is an intriguing process, which allows the synthesis of fuels and chemicals. One of the limitations for CO2 photoreduction in the liquid phase is its low solubility in water. This point has been here addressed by designing a fully innovative concept of pressurized photoreactor, allowing operation up to 20 bar and applied to improve the productivity of this very challenging process. The photoreduction of CO2 in the liquid phase was performed using commercial TiO2 (Evonink P25), TiO2 obtained by flame spray pyrolysis (FSP) and gold doped P25 (0.2 wt% Au-P25) in the presence of Na2SO3 as hole scavenger (HS). The different reaction parameters (catalyst concentration, pH and amount of HS) have been addressed.The products in liquid phase were formic acid and formaldehyde. Moreover, for longer reaction time and with total consumption of HS, gas phase products formed (H2 and CO) after accumulation of significant amount of organic compounds in the liquid phase, due to their consecutive photoreforming. Enhanced CO2 solubility in water was achieved by adding a base (pH= 12-14).In basic environment, CO2 formed carbonates which further reduced to formaldehyde and formic acid and consequently formed CO/CO2+H2 in the gas phase through photoreforming. The

Probing dissolved CO 2 (aq) in aqueous solutions for CO 2 electroreduction and storage

“…High CO 2 (g) pressure conditions are widely used for CO 2 capture, storage, and electroreduction in aqueous solutions ( 21 , 22 , 30 , 35 ). However, dynamic probing of CO 2 (aq) under these conditions is rarely reported, especially for CO 2 RR.…”

“…Conversion of CO 2 into fuels and value-added products via CO 2 electroreduction reaction (CO 2 RR) is an attractive approach to combating climate change and closing the carbon cycle ( 23 , 24 ). During CO 2 RR, it is widely accepted that the dissolved CO 2 (aq) is the active carbon species ( 25 – 28 ) reduced to CO, hydrocarbons, and oxygenates ( 29 – 32 ), and the reduction products are influenced by CO 2 (aq) concentration in the electrolytes ( 30 , 32 – 35 ). However, quantitative probing of CO 2 (aq) to correlate with CO 2 RR products is rare.…”

3D laminated graphitic carbon nitride decorating with 2D / 2D Bi 2 WO 6 / rGO nanosheets for selective photoreduction of CO 2 to CO

“…However, the CO 2 concentration is increased when the pressure is raised, resulting in the relatively low ratio of H 2 O/CO 2 . As mentioned in the previous report, 52 the high pressure might depress the productivity in the gas phase.…”