Excess CO 2 Reductions during CH 3 COOH Formation from CH 4 and CO 2 under Periodic Operation: Downhill Side Reactions in an Uphill Target Reaction under Unsteady Conditions.

Acetic acid (CH 3 COOH) formation from methane (CH 4 ) and carbon dioxide (CO 2 ) is an ideal reaction for chemical production, whereas this reaction possesses a severe thermodynamic limitation. To address this issue, it has been reported that periodic operation allowing a non-equilibrium condition can overcome the thermodynamic limitation. However, although an intrinsic issue of uphill reactions in non-equilibrium conditions generally is occurrence of unfavorable downhill reactions, this issue has seldom been discussed for the CH 3 COOH formation under periodic operation. Herein, excess CO 2 reductions were found to be the unfavorable downhill reactions possibly occurring in the reaction aiming at CH 3 COOH formation under periodically operated CH 4 and CO 2 feeds. The reaction using an isotopic reactant (i. e., 13 CH 4 ) unveiled that excess CO 2 reductions to CO and even to CH 3 moiety could occur, indicating importance of catalyst development. Furthermore, it was proposed that H 2 O vapor introduction into the CO 2 feed, which increased the CH 3 COOH product, most likely facilitated the reverse reaction of the excess CO 2 reductions and thereby is effective to hamper the unfavorable side reaction.