Bestimmung des aktiven zentrums und der reaktionspfade bei der dissoziation von N₂O in Fe-ZSM-5

Using a quantum chemical density functional method, the reaction mechanism of the decomposition of dinitrogen oxide in Fe-ZSM-5 on mononuclear iron oxide and hydroxide centers was studied. Mononuclear iron oxide centers may have value as a possible catalytic center. All kinetic data were determined for a reaction network of 46 surface species and 63 elementary reactions. All the transition structures, energy barriers, reaction paths, and reaction energies were determined. To determine the reaction paths and transition structures the newest search methods "growing string method" and "modified dimer method" were used. This allows a systematic study of reaction mechanisms without chemical intuition. Traces of water at 600-700 K significantly influenced the catalyst surface and kinetic data. The activation energy increased from 28.4 kcal/mole (1 ppb water) to 54.8 kcal/mole (100 ppb water). Mononuclear iron seems to be the active center in Fe-ZSM-5. Water in the smallest amount can poison the active iron oxide center at 600 K. At 700 K, this water desorbs. The reduction of dinitrogen oxide is an important ecological challenge because of its strong greenhouse effect. The iron zeolite catalyst, Fe-ZSM-5, is an active catalyst for the stoichiometric decomposition of N₂O into N₂ and O₂. During the decomposition of dinitrogen oxide in Fe-ZSM-5, according to G.I. Panov et al. (1990) an active oxygen species (α-oxygen) forms that can directly oxidize organic compounds selectively. The state of the iron in the zeolite pore structure and the reaction mechanism are despite comprehensive experimental and theoretical work still not clarified. The nuclearity especially of the active iron ions is unknown.