Quantum chemical and master equation study of OH + CH₂O → H₂O + CHO reaction rates in supercritical CO₂ environment

Abstract

We investigated the reaction rates of OH + CH2O → H2O + CHO at CO2 pressures of up to 1000 atm with and without CO2 molecule included in a reactive complex. Both mechanisms begin with formation of the hydrogen‐bonded prereactive complexes. Our ab initio calculations indicate a possibility of catalytic effect, predicting an activation barrier that one order of magnitude lower when the CO2 molecule is involved. To verify this effect, we use the Rice–Ramsperger–Kassel–Marcus theory and solve unimolecular master equations in the steady‐state approximation. We assume the equilibrium between prereactive complexes and reactants and compare the bimolecular reaction rates for the two mechanisms. The catalyzed reaction mechanism is found to be faster at higher CO2 pressures and lower temperatures, when prereactive complexes have nonnegligible concentration. Therefore, this catalytic effect may be important for this reactive process in room temperature supercritical CO2 solvent, but is unlikely to play a role during oxy‐combustion.