CO₂ conversion by high-dose rate electron beam irradiation: One-step, metal-free and simultaneous production of H₂, CO, CH₄, C₂H₆ and organic acids from an acid-decomposed CaCO₃/additive EtOH mixture

The reduction in CO₂ emissions is an important issue across many industries. Inspired by extraterrestrial organic matter formation, we herein report a CO₂ conversion approach based on high-dose rate electron beam (EB) irradiation of an acid-decomposed CaCO₃/additive EtOH mixture. With ¹³C-CaCO₃, ¹²C-EtOH and 100 kGy s^-1 EB, H₂, CO, CH₄, C₂H₆ and organic acids are simultaneously produced within a few seconds, except for 2,3-butanediol formation from excess EtOH. According to the organic analysis results, CO and organic acids contain ¹³C carbon derived from ¹³C-CaCO₃. The high-dose rate EB gives increased CO₂ conversion products compared to the low-dose rate EB. The CO₂ conversion yield/energy efficiency (product energy/input electrical energy) at 300 kGy is 1.51/0.50% in total (CO: 0.03/0.01%, formic acid: 1.31/0.29%, acetic acid: 0.05/0.04% and propionic acid: 0.12/0.16%), and the total radiation energy efficiency (REE, product energy/net radiation energy) of CO₂ at 300 kGy is 51.5% (CO: 0.90%, formic acid: 30.3%, acetic acid: 3.71% and propionic acid: 16.6%). The CO₂ conversion yield is ∼15 times larger than that of the only known CO₂ gas radiolysis (0.1%, CO only). Furthermore, the REE at 100 kGy is also ∼15 times higher than that obtained in the absence of EtOH. The energy input for the 100% conversion yield is estimated to be 38000 GJ per t-CO₂. The combination of the high-dose rate EB with organic additives facilitated CO₂ capture by radicals to afford improved CO₂ conversion efficiency/yield.