Kinetics and mechanism of the N2O reduction by NH3 on a Fe-zeolite-beta catalyst

In the context of decreasing the emissions of greenhouse gases, a Fe-exchan ged zeolite-beta (Fe-BEA) catalyst is shown to be very active in the reduct ion of N2O by NH3 in the presence of O-2. The temperature at which 50% N2O conversion is obtained is lower by ca. 80 K compared to its catalytic decom position in the absence of NH3. TPR, TPO, and TPD experiments after treatme nts in various atmospheres provide evidence that the reaction involves the redox cycle Fe-III <->Fe-II where the Fem active species are Fe oxocations of low nuclearity. N2O decomposes into O* surface species on specific reduc ed Fe sites with the concurrent release of N-2; these species do not compet e with O* coming from O-2 for their removal by NH3. In the absence of O-2, catalytic experiments with (N2O)-N-14 and (NH3)-N-15 show that: (1) N-2 is mainly formed from (NN)-N-14-N-14-O Splitting to yield N-14(2), the O* spec ies being in turn removed by (NH3)-N-15 to give N-15(2); (2) some N-14-(NO) -N-14 bond splitting occurs, which leads to (NN)-N-14-N-15 after reaction o f (NO)-N-14* and (NH3)-N-15 through a classical SCR mechanism. The Fe activ e species in the N-NO splitting are inhibited in the presence of O-2. The k inetics of N2O reduction by NH3 obeys a Mars and van Krevelen oxide-reducti on mechanism modified with an inhibiting term of NH3. (C) 2000 Academic Pre ss.