Influence of Cr(CO)6 and Mo(CO)6 on the critical conditions for ignition and the velocities of flame propagation for the chain-branching oxidation of hydrogen and propylene

It has been found that small additions (∼0.1 vol%) of chromium hexacarbonyl and molybdenum hexacarbonyl promote the combustion of a stoichiometric mixture of H₂ + O₂, resulting in a lowering of the lower limit of initiated ignition and an increase of the visible velocity of flame propagation; as this takes place, inhibition of propylene oxidation by the additives is observed indicating that hydrogen atoms do not play a noticeable role in chain branching in the initiated oxidation of hydrocarbons at room temperature; this indicates also that the kinetic mechanism of inhibition by carbonyls based on termination by the recombination of hydrogen atoms reported in the literature must be revised. Excited Cr atoms have been observed in a H₂ + O₂ flame in the presence of chromium hexacarbonyl.