Simultaneous photocatalytic CO2 reduction and C-C coupling of benzyl alcohol under high pressure and supercritical conditions

Carbon dioxide (CO2) utilization has received attention recently due to the negative impact of CO2 in the environment. One promising way to use CO2 is photocatalysis, in which light is used as a source of energy. However, photocatalysis is still very limited by low efficiency in the CO2 reduction. Here, we report for the first time the simultaneous photocatalytic CO2 reduction and benzyl alcohol activation under high-pressure and supercritical CO2 using a combination of cuprous oxide (Cu2O) and metallic copper (Cu0) as a photocatalyst. The CO2 photocatalytic reduction resulted in the formation of carbon monoxide (CO) as the main product. When using high-pressure CO2, the production rate of CO was increased by 125 times compared to the low-pressure process. This production of CO was further improved (2.3 times) when applying supercritical conditions. This significant enhancement in the CO production rate resulted in nearly seven times higher CO production rate compared to the current state-of-the-art Cu2O-based catalyst. When investigating the activation of benzyl alcohol, hydrobenzoin - the C-C coupling product - was identified as the main product (selectivity = 98 %). C-C coupling is highly attractive due to the challenges in obtaining these products through thermocatalysis. The process presented here has the potential to be applied using other photocatalysts in order to further enhance the CO production rate, offering a valuable alternative for CO2 conversion.