The kinetics of the reduction of NO to N2 by reaction with particles of Fe

The reaction (I) 3NO + 2Fe --> Fe2O3 + 3/2N(2) is important for converting the pollutant NO into harmless N-2 in combustion systems, particularly fluidized beds. Its initial rate has been measured thermogravimetrically at 1 bar and 500-900 degreesC for particles of Fe sufficiently small for the reaction to be kinetically controlled. A detailed analysis of the measured rates for a variety of [NO] and two different particle sizes indicates that the measured initial rate of disappearance of NO fits well to r = alpha(S)[NO]/(1 + (alpha(S)[NO]/beta(S))(1/2))(2) per unit surface area. The most likely mechanism involves dissociative adsorption of NO, followed by the desorption of N-2 and also O2- ions diffusing into the particle. There is another rate-law, which is almost as good, with the measured r = alpha(9)[NO](0.68). This rate expression could originate from NO adsorbing according to the Freundlich isotherm, followed by surface reaction to give N-2 and O2-. Kinetic parameters, together with activation energies and so on are all measured. Reaction I has a second stage, whose rate is determined by the amount of oxide product around each particle.