Density Functional Theory Study of Nitrous Oxide Decomposition over Fe- and Co-ZSM-5

Iron- and cobalt-exchanged ZSM-5 are active catalysts for the dissociation of nitrous oxide. In this study, density functional theory was used to assess a possible reaction pathway for the catalytic dissociation of N 2 O. The active center was taken to be mononuclear [FeO] + or [CoO] +, and the surrounding portion of the zeolite was represented by a 24-atom cluster. The first step of N 2 O decomposition involves the formation of [FeO 2 ] + or [CoO 2 ] + and the release of N 2 . The metal-oxo species produced in this step then reacts with N 2 O again, to release N 2 and O 2 . The apparent activation energies for N 2 O dissociation in Fe−ZSM-5 and Co−ZSM-5 are 39.4 and 34.6 kcal/mol, respectively. The preexponential factor for the apparent first-order rate coefficient is estimated to be of the order 10 7 s -1 Pa 1- . Although the calculated activation energy for Fe−ZSM-5 is in good agreement with that measured experimentally, the value of the preexponential factor is an order of magnitude smaller than that observed. The calculated activation energy for Co−ZSM-5 is higher than that reported experimentally. However, consistent with experiment, the rate of N 2 O decomposition on Co−ZSM-5 is predicted to be significantly higher than that on Fe−ZSM-5.