Effects of Water Molecule on CO Oxidation by OH: Reaction Pathways, Kinetic Barriers, and Rate Constants

The
water dilute oxy-fuel combustion is a clean combustion technology
for near-zero emission power; and the presence of water molecule could
have both kinetic and dynamic effects on combustion reactions. The
reaction OH + CO → CO2 + H, one of the most important
elementary reactions, has been investigated by extensive electronic
structure calculations. And the effects of a single water molecule
on CO oxidation have been studied by considering the preformed OH­(H2O) complex reacts with CO. The results show little change
in the reaction pathways, but the additional water molecule actually
increases the vibrationally adiabatic energy barriers (VaG). Further
thermal rate constant calculations in the temperature range of 200
to 2000 K demonstrate that the total low-pressure limit rate constant
for the water assisted OH­(H2O) + CO → CO2 + H2O + H reaction is 1–2 orders lower than that
of the water unassisted one, which is consistent with the change of VaG. Therefore, the hydrated radical OH­(H2O) would actually
slow down the oxidation of CO. Meanwhile, comparisons show that the
M06-2X/aug-cc-pVDZ method gives a much better estimation in energy
and thus is recommended to be employed for direct dynamics simulations.