NO2 inhibits the catalytic reaction of NO and O2 over Pt

The rate equation for the overall reaction of NO and O2 over Pt/Al2O3 was determined to be r=kf[NO] 1.05±0.08[O2]1.03±0.08[NO2]0.92±0.07(1-β), with kf as the forward rate constant, β=([NO2]/K[NO][O2]1/2), and K as the equilibrium constant for the overall reaction. An apparent activation energy of 82 kJ  mol−1 ± 9 kJ  mol−1 was observed. The inhibition by the product NO2 makes it imperative to include the influence of NO2 concentration in any analysis of the kinetics of this reaction. The reaction mechanism that fits our observed orders consists of the equilibrated dissociation of NO2 to produce a surface mostly covered by oxygen, thereby inhibiting the equilibrium adsorption of NO, and the non-dissociative adsorption of O2, which is the proposed rate determining step.